Stepstowards food webmanagement on farms
CENTRALE LANOBOUWCATALOGUS
0000 0807 2635
Promotoren:
Prof.Dr.Ir.E.A.Goewie
Hoogleraar indeMaatschappelijke AspectenvandeBiologische Landbouw
Prof.Dr.Ir.A.H.C.vanBruggen
HoogleraarindeBiologische Bedrijfssystemen
Co-Promotor:
Dr.W. Joenje
Universitair Hoofddocent, leerstoelgroep Gewas-enOnkruidecologie
Samenstelling Promotiecommissie:
Prof.Dr.Ir.P.C. Struik (Wageningen Universiteit)
Prof.Dr.Ir.L.Brussaard (Wageningen Universiteit)
Dr.G.R.deSnoo(Centrum voorMilieukunde,Universiteit Leiden)
Prof.Dr. T.Tscharntke (Georg-August Universitat, Gottingen)
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Steps towards food web management on farms
FransW. Smeding
Proefschrift
terverkrijging vandegraadvandoctor
opgezagvanderector magnificus
vanWageningen Universiteit,
Prof.Dr.Ir. L.Speelman
inhetopenbaarteverdedigen
opwoensdag6juni2001
desnamiddagsomhalftweeindeAula
1
>
IC
Smeding,F.W.,2001
Stepstowards food webmanagement on farms
Ph.D.Thesis,WageningenUniversity, -Withreferences-, Withsummary inEnglishand
Dutch
ISBN 90-5808-414-0
Subject headings:agroecosystem,farming system,biodiversity, food web,predator, organic
farming,pestmanagement, ecological infrastructure, field margin,Diptera, Carabidae,
Aranae,Skylark,Alaudaarvensis
M/UatfZol.M^a
Stellingen
1. Biologische landbouwbedrijven hebbenvoororganismen,hogerindevoedselketen,een
groteredraagkrachtvoorinstandhoudingvandebiodiversiteit danconventionele
landbouwbedrijven. Ditproefschrift.
Vergrotingvanhetvoedselaanbod aandebasisvanhetvoedselweb, iseenvoorwaardeom
detopdaarvantevergroten,hoewelterugkoppelingen,diediteffect tegenwerken ookte
verwachten zijn.Ditproefschrift.
3. Extrazorgvanboerenvoordeecologischeinfrastructuur, ondermeerdoorgerichtbeheer
vanslotenenslootkanten,heeft eensterkpositiefefFect opdebiodiversiteit vanhet
platteland.Ditproefschrift.
Deontrafeling vanhet menselijk genoomisbelangrijk,omdatditonderzoekde
verondersteldebepalenderolvangenen inlevendesystemen relativeert.
StephenJay GouldinNRCHcmdelsbladdd 20maart2001.
5. Deoorspronkelijke ideeenvandebiologischelandbouwzijndoorwetenschapperseerst
als'subjectief afgedaan, maarwordengestaagontdekt alsbruikbaar en'objectief .
Ecologischonderzoekmoetuitgaanvanniet-begrepenwaarnemingeninhetveldenmoet
deuitbreiding vandetheoriedaaraandienstbaar maken,inplaatsvandezevooropte
stellen.
7. WageningenUniversiteit stootstudentenafdoorretorischevragenentechnisch vernuft,
enzoustudenten aantrekken doorhettonenvantwijfel enzorgoveractueleproblemen in
delandbouw.
8. Hetopsteedsjongere leeftijd aanspreken vanrationelevermogensvankinderen leidttot
vervreemdingvandelevendeomgevingenasociaalgedrag.
Stellingenbij hetproefschrift vanFransW. Smeding,Stepstowardsfood webmanagementon
farms, 6juni 2000
Tomyfather andmother
whonurturedmyinterestandlove
ofnatureandthecountryside
andinmemoryof
PeterA.vanderWerff (1949-1996)
whogreatlyencouragedmeinthiswork
Preface
"Ourattention isdrawnbyablackbird screaming.ItisJanuary 28th and Iamwritingthis
thesis.Ilook throughthebedroom windowwithmywife and four-year-old sonandwewatch
a sparrow hawkwith ablackbird inhisclaws.And Iguessthathisvictim is"vlek"("spot"in
English),the female blackbird with onewhite feather ontopof eachshoulder, that lives
aroundourhouse.Impulsively Irandownstairs,throughthefront doorinanattempttorescue
theblackbird;butthesparrowhawk flies awaycarrying,ofcourse,itsprey".
That evening Ifelt abit confused aboutthisevent.Howcould abiologist studying food webs,
interfere with thehunt ofanimpressivebird ofprey?Perhaps ithelpedmetorealisemore
profoundly thattrophic interactions arenot figures buthavetodowithlife and death.ThenI
remembered anintriguing story from theHindu epicMahabharata, whichtellsofarighteous
kingwhoprotected afrightened dovefrom apursuing falcon. The falconbeggedthekingto
lethim eatandwarnedthekingthathisinterference with 'Dharma'(perhaps'naturalorder',in
thisthesis)wouldcreate fate. However,theking stucktohisprinciples andpromised the
falcon aquantity ofhisownflesh that equalled theweight ofthedove.Eventually theking
waseatentothebonesandboththe falcon andthedovelaughed attheking and flew away.
Although theMahabharata story ismysterioustome,itraises anassociation thatIhave
wantedtoput intothepreface ofthisthesis.Itconsidersthatthereisnodoubtthatman,as
part ofnature,should interfere inecosystemstofeed himself.However, ifhis interference
goesbeyondhisproperneeds,and are,sotosay,'noneofhisbusiness',hemaynotreally
knowwhatheisdoing andmaytherefore unwittingly disturbthenatural order. Thusthework
ofmodernbiologists likeRupert Sheldrakeconvinced methat currentbiology hasalimited
comprehension ofliving systems.A'righteousecologist'(whoisfor exampleinterfering with
food webs) should,therefore, remainmodest,whilstkeeping anopenmind and anopeneye,
bothwhen looking atnatureand athisownmotives.Thismighthelptoprevent hisworst
errors.Fortunately that afternoon myattempttointerfere withthehunting sparrowhawk
failed, becauseIwouldnothaveknownhowtocarefor aseverelywounded blackbird.
ThesmallmapsoftheFlevolandpolder inthisthesishaveaspecial meaning tome,because
they echothelargeembroidered mapoftheNoordoostpolder thathungonthewallofthe
diningroomwhen Iwasachild.Mygrandfather devotedhisprofessional life topolder
reclamation. Hispolder service employed outstanding ecologists likeW.FeekesandD.
Bakker,whowere engaged onboth applied andfundamental questions,whichwasmuch
appreciatedbymygrandfather (somyfather toldme).However the aimsofreclamation
concentrated onthematerial concernsof food andlabour,reflecting needsofsocietyatthat
timeandresulting inlarge scaledrational landscapes.Following thistradition my father
contributed tothedevelopment of agricultural education. Itismy sincere andmodest wish
thatmycurrentwork maycontributetotheimplementation ofawider scopeof agricultural
production, andaddressthephysical aswell astheemotional andspiritualneeds.
Without the support ofmanypeople,thisthesiswouldneverhavebeen accomplished. Iam
grateful to:
Mypromoter EricGoewiewhogavemespace andconfidence tobegintheproject, andwho
strengthened mybackbone and inspired meinmomentsofhesitation.Mypromoter Ariena
vanBruggenwho,after her arrival inWageningen,needed only ahalfwordtounderstand the
contents ofthework andhelped metoprocessthepiled-up field data.My co-promoter
Wouter Joenje, withwhom Isharecommoninterests inecologicaltheories and field biology,
particularly ofpioneer successional stages andthepolders.
Thefunding organisation (LNV-DWK) for supporting asmallresearch group sothat they
couldembarkuponaproject withanuncertain outcome.Howeverthisresearchgroupwas
much strengthened thankstotheinvaluable co-operation andfriendship oftheresearchersof
PlantResearchInternational (formerly IPO-DLO):KeesBooij, ClasienLockandLoesden
Nijs.
Thesupervision committee oftheproject 'Foodwebmanagement onfarms', that
enthusiastically guidedtheresearchbyit'sreflections onourplans andresults.Thecommittee
included:GeertdeSnoo(CML-Universiteit Leiden),FrankvanBelle (Vereniging
Natuurmonumenten),PaulAukes (IKCNatuur),Paul vanHam(IKCLandbouw),Tibbe
Breimer (LNV-DWK), aswell asKeesBooij, WouterJoenje (thechairman) andEricGoewie.
Myresearch assistant, AndreMaassen,whowas apillarofstrengthwith all our laborious
activities,thedesignerofinstruments andforms, companion ofthehundreds ofkilometres
walkedwhiledatacollecting,andtheonewhocould, ifasked,alwayshelpmeremember the
aimsofmywork.
TheMSc studentswhodidreconnaissance work for thethesis:ElkeBoesewinkel, Jacintade
Huu,NathalieReijers, JulienCothenet, Edwin Coomans,HongNan, andinparticularBart
Venhorstwhoalso supported thefield work andinsect identification.
Peoplewithwhom Iexchanged ideasorwhoprovided valuable information that contributed
tothisthesis:GerardOomen,WillemBeekman,JanDiekvanMansvelt, Sjaak Wolfert,
DorineDekker,DerkJan Stobbelaar,KarinaHendriks,DarkoZnaor,Prof.R.A.A. Oldeman,
Ruurdtje Boersma,ManolisKabourakis,AnorFiorini,HansEsselink (whonamed
'Voedselwebbeheer'), Joop Schaminee,JohnVandermeer, YvettePerfecto, JulianPark,Nigel
Boatman,FlipvanKoesveld,JanJaapvanAlmenkerk,Wolter vanderKooij, RobBoeringa,
HenkKloen,YvonnevandenHork,MoniqueBulle,membersofthePE-Phd discussion group
'Plant and CropEcology',PaulaWesterman, Eefje denBelder, Walter Rossing.
Thefarmers whoallowedmeaccesstotheir farms andwhogavetheirtimetoanswermy
questions;inparticular, especial thanks areduetoMaartenPietvanAndel,CarlenRini
Ferket, JanenMarleenvanWoerden-Zeelenberg, Lex enJannieKruit, HenkLeenstra, EvertJanRienks,JansjeTimmermans,DouweMonsma,HemandMarjon Cuppen,staff and
residentsof'Thedinghsweert'for theirhospitality and interest.
JoopOvervest,JohanJorink, HarryAlting andcolleagues (staff andworkersoftheA.P.
Minderhoudhoeve), Swifterbant, andEgbert Lantinga (chairman oftheresearch team) for
discussingmyresearch andimplementing recommendations onthe ecological farm.
Allthepeoplewhodidtheorganisation behind theproject, particularly Gijsbertje Berkhout.
ThestaffofUnifarm whowerealwayswillingtosupportthe project.
Colleagues oftheBiological Farming Systemsgroupwhoaccepted myabsence,whilst
encouragingmeto finish mythesisresearch.
NickyCampbell ofCombpyne,Devon,UKfor correcting theEnglish. Wampievan
Schouwenburg for helpwiththe final editing.
HeleenBoerswhohelped metocollectmyself.
Andlastbut notleastmydear friends and family who supported and encouraged me,andwith
someofwhom Icould sharemyaspirations:Annelies,Francis,Philip,mybrother Guido,my
uncleKeesCleveringa;butmost ofall,EliseandTimowhogavemewarmth atthecoldest
momentsofmypersonal 'Winterreise'.
Abstract
Thispaperisthereportof four yearsofresearch onthefunctional group composition ofthe
animalcommunity inrelationtofarm andecological infrastructure (E.I.)management on
organic arable farms. Theresults aremainlybasedonabundance dataofground dwelling
arthropods obtained bypitfall trapping,densitydataofvegetation dwelling arthropodsby
vacuum sampling anddensitydataofinsectivorousbirdsbyterritorymapping. Arthropods
were collected inwheat crops (representing thecroparea)andontheadjacent canalbank
(representing theE.I.);thebird, farm andE.I.variablesweremeasured atthe farm level.
Studyareasincluded intotal 18farms withvaryingextentsoforganicduration, croprotation
intensity, andquantity andquality ofE.I.
Thehypothesis oftheresearchwasthatthefood webstructureofanorganicarablefarm with
longorganic duration aswell aswith animproved E.I. (i.e.enlarged, latemown),would show
ahigher abundance ofmeso-andmacrofauna ofbothherbivorous and detritivorous functional
groups.Theseenhancedprimary groupswereexpectedtocarryahighpredatorabundanceat
both secondary (i.e.invertebrates) aswell astertiary(i.e.birds) levels.Withregardtothecrop
areasitwas found, incontradiction tothehypothesis,thatherbivores weremost abundant in
crop areasofrecentlyconverted farms andoforganicfarms withintensivecroprotation;this
herbivore abundance was associated withinvertebratepredator abundance and species
diversity. Inaccordance withthehypothesis, someevidencewas found for increased
detritivoreandrelated epigeicpredator abundancerelatedtoextensivecropmanagementon
thefarms oflongorganicduration. Whilst studyingtheE.I., anincreased abundanceof
vegetation dwellingpredators andalsodetritivoreswasfound inimproved E.I.However Kherbivore numbersdidnot increaseintheimproved E.I.whentheywerecomparedtothe
traditionally managed E.I.The summerabundance ofepigeicpredators wasalsonotrelatedto
animproved E.I.Field studiesprovided someevidence forthedispersal of functional groups,
abundant intheE.I.,towardsthecroparea.However, the effects ofcropconditions onthe
arthropod abundance inthecrop areawereobserved tooffset the influence oftheE.I.Bird
studies atthe farm levelrevealedpositive correlation betweenbird functional groups anda
combination ofcrop areaandE.I. characteristics.Bird densitywas found tobepositively
associatedwithhigh arthropod abundance intheE.I.vegetation canopy. Observations also
suggested positive correlation to anincreased herbivory inthecrop areaofthelongduration
organic farms that had anintensive croprotation.
Aproposal for adescriptive ortopological farm food webisdrawn from field observations as
wellasfromreferences inliterature.Predictions aremade for four different farm food web
structures that express four extremes oftwoenvironmental gradients,which correspond tothe
length oforganicduration andtheamount/quality oftheE.I.Withreference tofield
observations important themesinthe food webtheory arediscussed, includingtheindirect
effects ofsubsidised detrital food chains onherbivore abundance andconsequently onbird
abundance, aswell asthepossible effects ofintraguildpredation onarthropod functional
group composition.
Theimplications ofthestudy arethatorganic duration andthe amount/quality oftheE.I.may
contribute to improving ecosystem services andtoaimsbased onnature conservation.
However anoptimisation ofthe farm food webwithregardto ecosystem servicesmaynot
necessarily improvenature conservation values.Itisargued that increased understanding of
the farm food webanditsmanagement islikelyto support thedevelopment of multi-species
agroecosystems thatintegrate improved ecosystem services andnatureconservation goals.
Notes
Thisproject wasfunded bytheMinistryofAgriculture,NatureManagement andFisheries,
Department of ScienceandKnowledge Dissemination.
Chapters2,3,4 and6havebeen submitted forpublication ininternationaljournals.
Tableofcontents
Chapter 1: General introduction
1
Chapter 2: Functional groupcompositions ofvegetation dwelling arthropods inrelation
toecological infrastructure andtime sinceconversion toorganic farming
Smeding, F.W., A.H.T.M. Maassen&A.H.C. vanBruggen
5
Chapter 3: Shifts infunctional groupcomposition ofgrounddwelling arthropodsin
relationtoecological infrastructure andconversion toorganic farming
Smeding, F.W., CAM. Lock &C.J.H. Booij
31
Chapter4: Insectivorousbreedingbirds onorganic farms inrelationtocroparea,
ecological infrastructure and arthropods
Smeding, F.W. &C.J.H. Booij
Chapter 5: Effect offieldmarginmanagement oninsectivorousbirds,aphidsand
theirpredatorsindifferent landscapes
Smeding, F.W. &C.J.H. Booij, 1999.
AspectsofAppliedBiology54:367-374.
Chapter 6: Aconceptof food web structure inorganic arable farming systems
Smeding, F.W.&G.R. deSnoo
51
75
83
Chapter 7: Farm-NaturePlan: landscapeecologybased farm planning
Smeding, F.W. &W. Joenje, 1999.
Landscapeand Urban Planning46:109-115.
101
Chapter 8: General discussion
109
References
117
Summary
131
Samenvatting
133
Curriculum vitae
137
Chapter 1:General introduction
Thisthesis ismotivatedbyconcernsaboutbiodiversity loss,duetoagricultural intensification
(Altieri, 1994,1999;Paoletti, 1999;Wood &Lenne, 1999;Vandermeeretal, 1998)andis
primarily concerned withplant and animal speciesindigenoustoagricultural landscapes.
Biodiversity losshasbeenthought toresult inartificial ecosystems,requiring constant human
intervention andcostly external inputs.From thisperspectivebiodiversity has economical
value,related toitsecological services,e.g. pest control andbioticregulation of soil fertility
(Altieri, 1994, 1999;Pimentel etal, 1995).Natureconservationworthy speciesmayhaveno
evident significance for the functioning ofagroecosystem (Duelli etal, 1999).Howeverit
canbe arguedthat agriculturehas,toacertain extent,responsibility for allspeciesand
communitieswhichco-evolved with farming during around 10,000years(Wood &Lenne,
1999),irrespective oftheir utility.
Oneimportant solution for thereversal ofbiodiversity lossinconventional agricultureof
industrialised countriesisthedevelopment of farming systemsthat areeconomically basedon
utilisation ofbiodiversity andthat alsoharbour conservation worthy species.Thisideais
compatiblewith theconcept ofmulti-species agroecosystems (Vandermeer etal, 1998;
Altieri, 1994, 1999;Almekindersetal, 1995;Swift &Anderson, 1993).Development of
organic farming systems isapossible implementation ofthis concept (Stobbelaar &Van
Mansvelt, 2000;Vandermeer, 1995; VanderWerff, 1991).Theadoption ofthisconcept in
thecropareamaybecomplemented byanappropriatemanagement ofthe semi-natural
habitat onthe farm, whichisdefined asthe ecologicalinfrastructure (E.I.)(Smeding &Booij,
1999).
Afood web approach isanappropriatemethod for investigations intothehigher integration
levelsofecosystems (Polis&Winemiller, 1996;Pimm, 1991; Gezondheidsraad, 1997).This
approach istherefore suitable for fanning systemsresearch.Progress in scientific
understanding offood websiscurrently expanding intoagroecology asisdemonstratedby
articlesoninteractionsbetween detrital andherbivore subsystems (Brussaard, 1998;Wiseet
al, 1999)andamongpredator functional groups(Tscharntke, 1997).Theseinteractionsmay
affect theabundance of functional groups,cropperformance aswell asdecompositionrates.
Complementary tofunctional analysis,afood webapproachmight alsooffer acomprehensive
framework for the scattered information onfarmland species andhabitats (De Snoo&
Chaney, 1999).
Asimplified setofhypotheseswithregardtofood web structureonorganic farms servedas
the startingpoint for thefieldresearchofthisthesis:itwasexpected thatthe durationof
organicmanagement, extensive croprotationaswellasanimproved E.I.(i.e.enlarged area
and latemowing date),wouldrelatepositively totheabundance ofnon-pest primary
arthropod functional groups(Kromp&Meindl, 1997):thedetritalwebwouldbeenhancedby
theincreased input oforganicmatter, consisting oforganicmanure,compost andcrop
residues(ofcereals,leypasture);non-pestherbivorenumberswouldbeenhancedbycrop
diversity aswell asweed diversity (Hald&Reddersen, 1990)and inparticular wouldbe
boostedbythevariedplanttissues(Curry, 1994;Tscharntke &Greiler, 1995)whichoccurin
improved E.I. Consequently predator andparasitoid numbers onthe farm wouldbe supported.
Anaccumulatedhigh invertebratedensityonthefarm wouldsupport insectivorous
vertebrates,particularlybirds (e.g.Poulsen etal, 1998).
Theobjectives ofthisthesiswere:
- Toanalyseandconceptualise food websonorganic arable farms that encompassthe
important above-andbelow ground functional groups andthat canberelated to farmers'
decisions about, for example,croprotation andmanuremanagement, farm lay-outand
field margin management;
- Tolinkknowledge ofthebiology ofgroupsofindividual species,crop and vegetation
managementtofood webtheories,andtoidentify possiblefood webmediated factors that
mightinfluence theabundance of functional groupsonthe farm;
- To suggest strategies for development of farming practicesthat strivetopromote
ecological servicesandconservation ofspecies.
Tomeettheobjectives, field research andanalysisof literature datawereundertaken.The
study areainvolved organic arable farms thatweremainly situated inFlevoland. Thisregion
waschosenbecause ofitsuniformity intopography andhistoryandbecauseoftheoccurrence
ofaround 75organic farms including farms with improved ecological infrastructure, resulting
from aprototyping researchproject (Vereijken, 1997,1998).
Empirical investigations wereconcentrated onparticular sectionsofthefarmland community.
Functional group compositions (e.g. detritivores,herbivores andpredators)within these
sectionswereassessed. Allthreeempirical chapters start from thesameinitial setof
hypotheses explained above,andreflect toacertain extent oneachotherintheirdiscussions.
Observations onvegetation dwelling arthropods onthirteen farms (Chapter2)arepresented
first, becausethis section included largeproportions ofallthreemajor functional groups,
involving especially herbivores and connectedpredators.
Observations onground dwellersoneight farms (Chapter 3)included numerous epigeic
predatorsthat aresupposed tohold akeyposition inthe farm food web.Howeverthisgroup
appearstobemore stronglyrelated tothedetrital subwebthantotheherbivore subweb.
Densities ofbirdterritories onten farms (Chapter4)arerelated tovariables ofboth vegetation
dwelling andgrounddwelling arthropods aswell astofarm and ecological infrastructure
traits.Birdsrepresent vertebrates,thatmightbe supported byanincreased abundanceofprey
from theherbivore subweb aswell asthedetrital subweb.
Chapter 5includes alandscape comparison between ayoungpolder landscape (i.e.Flevoland)
andalandscape thathasbeen farmed for many centuries (i.e.river region).This explorative
studyplacestheobservations inFlevoland into abroader geographical context.
Aproposal for adescriptive ortopological farm food web (Chapter 6)isdrawn fromfield
observations aswell asfrom references intheliterature. Important themes inthe food web
theory aretentatively applied tothispreliminarymodel, explaining differences between local
farm food webstructures andhowthey arerelated tofarm and/orE.I.management. Theinitial
setofhypotheses onwhichthefieldworkwasbased, ismodified intomore elaborate
hypotheses.
Anadditional chapter (Chapter 7)dealswithplans for thecoexistence offarm andnatural life.
Itpresents apragmatic advisory instrument that structures expertjudgement. The instrument
isbased onacombination ofecological theory andfieldbiology.However results ofthe food
webstudy arenot included sincetheinstrument (Smeding, 1995)was developed earlierand
wastherefore anincentivetothe food webstudies ofthisthesis.
Thediscussionchapter (Chapter 8)considersbriefly theimplications oftheresearch forthe
development ofmultispecies farming systems.
Itmustbenoted that compared tothechronology oftheinvestigations,chapters2-5 arein
reverseorder.Theproject startedwithanassessment of farms indifferent landscapes (1997).
Howeverthestudyareaincludedtoomuchvariation andtoofew sitestobe analysed
statistically. Therefore investigations inthe following year (1998)wereconfined toamore
uniform areainFlevoland. Howevertherelationsbetweenground dwelling functional groups
andthefarm andE.I.variableswere,atfirstglance,difficult tointerpret and showed little
coherencewiththebird data.Theherbivore subwebofthe farm food webwasexpected, and
wasalsofound, togivebetterdistinctions,withregardtoinvestigated variables. Consequently
vegetation dwelling arthropodswereassessed in 1999.
Chapter 2:Functional group compositions ofvegetation dwelling
arthropods inrelation toecologicalinfrastructure and timesince
conversion toorganic farming
F.W. Smeding,A.H.T.M. Maassen &A.H.C.vanBruggen
Department ofPlant Sciences, Biological Farming Systems group, Wageningen University, Wageningen,The
Netherlands
Abstract
Hypotheses onthe relation offarm management and ecological infrastructure (E.I.) characteristics tothe
functional group composition ofvegetation dwelling arthropods inthe crop and E.I.were tested on organic
arable farms. The study area included 13farms that varied withregard tothe studied traits.Arthropods were
collected by vacuum trapping inwheat crops and adjacent boundaries. Observations inthe crop area suggested
that bothorganic duration and farm 'intensity' affect thearthropods. In contrast toexpectations from the
literature, K-herbivores and associated predators were most abundant inthe luxurious crops of recently
converted farms. Long duration organic farms with anintensivemanagement, seemed tobe most prone torherbivore outbreaks, associated with species-diverse but not numerous predators. In support ofthe expectations,
some evidence was collected for an increase of detritivores onlong duration farms with an extensive crop
rotation. Observations inthe E.I. showed that, according tothe expectations, improved management (i.e. large
area and late mowing) enhanced predators and also detritivores.However, herbivore abundance was similarly
high in traditionally managed E.I. Effects ofhigh abundance ofarthropod functional groups inthe E.I. on
dispersal intothe crop,were largely offset by crop conditions. Possible indirect effects of subsidized detrital food
chains onherbivore abundance, as well as effects of intraguild predation on arthropod functional group
composition, are discussed with reference to field observations.
1. Introduction
1.1. Agricultureandbiodiversity
Thebiodiversity offarms andagricultural landscapes inindustrialised countrieshas decreased
dramatically (e.g. Andreassen etal, 1996;Fuller etal, 1995;Aebischer, 1991).This
biodiversity-loss isamatter ofgreatconcern for ecologists,agriculturists aswell aspoliticians
(Paoletti, 1999;Wood &Lenne, 1999).Toreversethistrend ofbiodiversity-loss, farming
system innovation isprobably needed (Altieri 1994;Vandermeer etal, 1998;Almekinderset
al, 1995;Swift &Anderson, 1993).Oneoftheoptionstoenhancebiodiversity istopromote
on-farm natural areasthat couldbevaluable forbothproduction aswell asfor nature
conservation aims.
Thetotal areaof semi-natural habitat onthefarm isalsocalled the'ecological infrastructure'
(E.I.).Fieldmarginsareamajor constituent oftheE.I.(Smeding &Booij, 1999).Agricultural
production couldbe enhanced byvariousecological functions ofthis E.I., such asregulation
ofpestsbypredators andparasitoids,nutrient cyclingbysoilorganisms, andpollinationby
various arthropods.Forexample,biodiversity ofarablefield margins significantly contributed
todensities onthefarm ofpredatory invertebrates,butterflies, birds andmammals(e.g.
Boatman etal, 1999;Joenje etal, 1997;LaSalle, 1999).
1.2. Farmmanagementandon-farm communities
Despitetheincreasing amount ofinformation onfarmland speciesandvegetation, thereisstill
fragmentary knowledge oftherelationshipsbetween farm managementpractices and farm
communities (DeSnoo&Chaney, 1999).Forexample,croprotation, fertility level,weed
control,field size,anddistribution andmanagement offield marginsmay all affect farm
community composition.
Managementpractices onorganic farms corresponding toproduction guidelines 2092/91in
theECcountries(Anonymous, 1991)areessentially different from thoseon conventional
farms. Inparticular, maintenance andpromotion ofbiodiversity isinherent tothephilosophy
oforganicfarming. Therefore, organic farms could function asastepping stoneontheroadto
developingrational,biodiverse farming systems (Stobbelaar &VanMansvelt,2000).
However, information onthetrophicstructure ofanimalcommunities atthe farm levelisstill
scattered andincomplete for conventional aswell asorganic farming systems (e.g. Kromp&
Meindl, 1997;Isart&Llerena, 1995).Bothempirical andexperimental research atthe farm
level isrequired tofillthegapsintheknowledge ofeffects ofconversion from conventional
toorganic farming andoffieldmarginmanagementpracticesonagroecosystem community
composition.
Research addressing thewhole'biocoenosis'isneededtounderstand theeffects of
management practices onagroecosystem functioning (Biichsetai, 1997).Recent advancesin
research offood webs(Polis&Winemiller, 1996),including somestudies in agricultural
habitats(DeRuiteretai, 1997;Tscharntke, 1997;Wiseetal, 1999),areproviding inspiring
examples ofhow(agro)ecosystems canbe approached atintegration levelshigherthanthe
species-level. Someofthisresearchindicatesthat foodwebs canmediate theeffects of
environmental stress factors onspecies(Winemiller &Polis,1996).
1.3. Hypotheses andobjectives
Detritivorenumbersareenhancedbytheincreased organicmatterinput,involving organic
manure,compost and cropresidues(ofcereals,andleypasture)(e.g. Pfiffner &Mader, 1997;
Weberetal, 1997;Idinger etal, 1996;Heimbach &Garbe, 1996).Non-pest herbivores are
enhanced bycropandweeddiversity (Hald&Reddersen, 1990;Moreby &Sotherton, 1997;
Andow, 1988).Moreover, the effects oforganicdurationmay continuetowork cumulatively
overyears,with regardtoboth detritivores (Idinger &Kromp, 1997)aswell asherbivores
(Hald &Redderson, 1990).Theabundance ofprimary functional groupswould support
predacious functional groups ofe.g. epigeicpredators (Kromp, 1999;Wiseetal, 1999),
predacious flies andparasitoids (Idinger &Kromp, 1997).Theincrease ofpredator abundance
maysubsequently depresspest-herbivores (Altieri, 1994),provided that crops arenottoo
muchaffected byherbivores (VanEmden, 1988).Basedontheseobservations,we
hypothesisethat farms thathavebeenorganic formanyyears,havehigher densitiesofnonpestprimary functional groups (both detritivores andnon-pest herbivores) andtheirpredators
inthecropareathan farms thatwere converted recently.
Additionally wehypothesise that appropriately managed E.I.will support largenumbersand
diversity ofnon-pest herbivores,predators andparasitoids both in field margins andcrop
areas.Anincreased varietyinplanttissuequality andamorevariedvegetation structure are
assumedtobekey factors (Curry, 1994;Feberetal, 1999).Alsomown grass strips,less
complexthanmost otherboundaryhabitats,contributetoresources for these groups (Barker
etal, 1999;DeSnoo&Chaney, 1999).Anincreased amount and spatial density ofE.I.
6
affects thepopulations intheadjacent croparea,involvingbothherbivores (Holland&
Fahrig,2000)andpredators (Lys&Nentwig, 1992;Sunderland etal, 1996a).Inadditionto
organicduration, croprotationintensity andE.I.characteristics (withregard toquantityand
diversity),other farm management factors areexpected toinfluence the functional group
composition ofvegetation dwelling arthropods.For exampletheeffects ofthestudied factors
maybeoffset orenhancedby cropperformance. Totaketheseinfluences into account some
cropvariables, indirectly related tovariablescentral inthehypotheses, arealsoincluded inthe
study.
However,theabove-stated hypotheses about theeffects oforganic farming duration andE.I.
management onvegetation dwelling arthropod functional groupshavenotbeentested so far.
Thus,theobjectives ofthis studywere:
1. todeterminethedensity anddiversity ofvegetation dwelling arthropod functional groups
inthecroparea andsemi-naturalfieldmarginsonorganic farms, andrelatethedensity
anddiversityofthesegroupstocropareaandecological infrastructure characteristics;
2. todetermine iftherearedistinct species compositions ofvegetation-dwelling arthropod
functional groups among farms differing incropareaandecological infrastructure traits;
3. torelate abundance anddiversityofvegetation arthropod functional groupstothedistance
from theecological infrastructure.
Ourstudywas focused onvegetation dwelling arthropodsbecausethisgroup comprisesboth
detritivores,herbivores,predatorsandparasitoids.Inmanystudiestheherbivore subwebis
notwellrepresented,particularly whenpitfalls areused,whichprimarily collect epigeic
predators (Duelli etai, 1999).
N
W -*4^" E
S
10
20 Kilometers
s
Fig. 1.Study area. Theinvestigated organic arablefarms arerepresented by closed circles.
2.Materials and methods
2.1. Studyarea
Thestudywasdoneonorganic farms andoneintegrated farm intheprovince ofFlevoland,
TheNetherlands.Thefarms arelocated within a280km2areainthepolder Oostelijk
Flevoland (Fig.l). Thispolderwasreclaimed in 1954andisdominated by agricultural
landuse.Thesoilisacalcareous clayofmarineorigin.Flevoland waschosen asastudyarea
becauseithas aconcentration of75organic arable farms that aresimilarwithregardtotheir
history andtopography.
Inthe study area 13farms were selectedthatdiffered invarious farm structure and ecological
infrastructure (E.I.)traits(Table 1).Together thefarms comprised 656haarable land.The
selection included eleven commercial organic farms andtwoexperimental farms. Threeofthe
selected arablecommercial farms reared livestock whichwere fed onhomeproduced fodder
inthewinter,butweregrazed elsewhere duringtherest oftheyear(farms T,Kand S).The
experimental farms ofWageningen University (farms EandI)aremixeddairy and arable
farms; farm Eisorganicand farm Iisintegrated. FarmIisdivided intotwopartsbyaroad
andonlythenorthernpartwasincluded inthestudy area.Threecommercial farms (T,Land
S)wereEcological ArableFarming Systems (EAFS)prototype farms during 1992-1997
(Vereijken, 1997,1998).
2.1.1. Crop area characteristics
Theorganic duration oftheselected farms ranged from onetosixteenyears.Ploughing is
generally at25-30cmdepth. Onallthe farms a6-7 yearcroprotation ismaintained, including
per farm 11-41%cereals,0-18%leypasture, 12-43%traditional lifted crops (potatoes,sugar
beet) and25-67%vegetable crops.Thevegetables grownweremainlyonions,peas,sweet
corn,various cabbages,andrunnerbeans.The farms withthemostintensive croprotations
hadupto60%vegetables andtherefore alowerpercentage (<20%) ofgramineous crops
(cereals,andleypasture).Becausetheinputofnutrients (N,P,K)hastobe adjusted tocrop
requirements, andvegetablesneedmorenutrientsthancereals,intensity ofcroprotationis
assumedtorelatetothe amount ofNapplication atthe farm level.Compared withother
crops,gramineous cropsprovide alarge amountofcarbon incropresidues andrequire few
soil disturbing operations.
2.1.2.EcologicalInfrastructurecharacteristics
TheEcological Infrastructure (E.I.)ofarablefarms inFlevoland ismainly determined by
canals andbanks(together c.3-4mwidth),that arelaidoutaslinearherbaceous boundaries
adjacent tothecrops.Onfive farms,boundaries arewiderbecauseof adjacent (2-3mwide)
grassstrips,often including clovers (Trifolium spp.),ononeorboth sidesofthecanals.Farm
E alsohasgrassstripsbetweencropplots.Percentages ofE.I.higher than c.2%(Table 1)
weremainlyduetothepresence ofthesegrass strips.Onlyfarms Land Epossessed a
boundaryplanted with ahedgerow. Spatial density ofE.I.ispurposefully increased on farm E
(Smeding &Joenje, 1999)and farm L.Thespatial arrangement ofE.I.ontheother6 farms
mainlyreflects landscape scale.
Extremetypesofvegetationmanagement are:
- 'traditional management' involving threeor four morecutsperyearwith aflail mower
leavingtheshredded cuttings in situ;
- 'latemowing management' involving oneortwocutsperyear after June 21st with a fingerbarmowerwith hiabgrab for removal ofcuttings.
Thegrass stripsalongthecanals in'latemowingmanagement' arerequired for transport. The
E.I.area is,therefore, related tothemowing date.InthisarticletheE.I.with enlarged area
and latemowing isdefined as'improved E.I.'.Theimproved E.I.onthefour farms A,T,L,
andDwascreated duringtheEAFS-prototyping researchprogram in 1992-1997 (Vereijken,
1997,1998).Theimproved E.I.ontheexperimental farm Estarted in 1995 simultaneously
with conversion oftheconventional dairy farm toanorganicmixed farm (Smeding&Joenje,
1999).
Table1
Thecharacteristics of thefarm, thewheat crop and the ecological infrastructure (E.I.) on the thirteen selected
farms.
c/1
00
Q
^
_;
_;
&
&
op.
O
u
o
3
ui
ui
w
00
o
en
1™
c
c
rt
3
T3
J3
o
o
3
.3
o
rt
I
00
o
o
c
<4-l
a
o
ed
"3
3
I-*
V3
a
o
O
>
>
o
O
o
t-H
1
3
VI
gVi
3
&Q
O.
C/3
Variable: dur area
unit: year %
Farm:
level/habitat: farm farm
K
organic, arable
16
1.8
J
organic, arable
11 4.4
S
organic, arable
11 3.2
L
organic, arable
11 3.1
O
organic, arable
11
1.1
T
organic, arable
9 2.3
F
organic, arable
8
1.4
E
organic, mixed
5 4.5
B
organic, arable
2
1.4
R
organic, arable
2
1.2
H
organic, arable
1 1.5
Z
organic, arable
1 1.2
M
0 2.0
integrated, mixed
int
ccov
ucov
%
%
%
farm
30
26
35
18
50
31
35
55
17
11
27
17
65
crop
71
64
76
66
73
69
28
86
86
63
78
79
87
crop
28.6
7.1
7.5
7.8
5.1
9.4
2.3
16.4
0.3
25.6
5.7
0.0
1.7
uspn
n/m2
crop
1.8
4.0
2.7
3.1
4.4
2.7
2.6
3.6
0.4
3.6
1.3
0.2
1.6
l
l
.2-
>
<4-
o
o
00
>
'o
Q
00
Q
o
O
mow eicov
month %
E.I.
E.I.
5
64
6
92
7
89
7
88
6
89
92
9
5
73
11
97
5
91
5
76
5
96
5
90
5
68
eispn
n/m2
E.I.
2.1
4.4
5.8
5.1
4.9
4.2
2.7
5.1
4.4
3.2
4.0
3.4
6.2
Dominant plant species incanalbank swardswere:couch (Elymus repens),perennial meadow
grasses (Festuca rubra,Poatrivilais, Loliumperenne,Agrostisstolonifera),commonreed
(Phragmitis australis)and afew perennial herbs:dandelion {Taraxacum officinale) and
stinging nettle(Urticadioica).Canalswithtraditionalmanagement have alow,relatively
open, speciespoor vegetation (<10species/4m2),dominated byafew grass species.Late
mowingparticularly related toincreased vegetationbiomass inJune andJuly asexpressedby
vegetationheight(upto 1-3 m)andcover(upto90-100%).Howeverlatemowingdoesnot
necessarilyrelatetoincreased higherplant species diversity for tworeasons:a)tallgrass
speciesmaydominatethe sward;b) swards oftraditional management may locallybecutto
ground levelandtherefore beinvadedbyruderalsand annuals(increased speciesnumberup
to 15species/4m ),e.g. thistles (Cirsium arvense, Sonchus arvensis),annualweeds(e.g.
Sonchusasper,Polygonumaviculare)and annualsthat arerarelypernicious weedsin
Flevoland (e.g. Myosotisarvensis, Veronicapersica, Cardaminehirsuta).
Highperennialplantdiversities found insomelocationsmayrelatetovarious interrelated
factors:reduced vegetationproductivity,removal ofthehay,nutrient buffering bythegrass
strip,and longorganicduration. However, also,artificial speciesintroduction isinvolved;in
theEAFS-project, around 90different nativeperennial dicotswere artificially seeded inthe
canalbankstoobtainhigherplant diversity and flower abundance ofplantswith limited
dispersal capacity (Vereijken, 1998).Although few specieswereabletosettlewell(e.g.
Seneciojacobea, Crepisbiennis,Heracleum sphondylium), the introduction clearly affected
speciesdiversity:vegetation including siteswith>15species/4m2wereconfined toprototype
farms.
2.2.Samplingandmeasurements
2.2.1.Arthropods
Sampling ofarthropods wasdoneinwheat crops andinadjacent canalsbanks(E.I.).Spring
wheat (Triticum aestivumL.)waschosen asarepresentative crop asthis cropiscommonon
organicarablefarms inFlevoland and arthropodnumbersincereals arelargecompared to
numbersinothercommoncrops likepotatoes andonions (Booij &Noorlander, 1992).Within
onewheatfieldoneachofthe 13farms one 50x30msampling areawas selected;thisarea
was50meterlongbordering acanalby30mperpendicular tothatcanal.Nineplotsof 1 m2at
distancesof0m(E.I.), 10m(wheat) and30m(wheat) from thecanalbankwere selected for
measurement ofarthropods,crop,weedandE.I.-vegetation variables.
Distance from thetopofthecanalbanktothecropedgeofthewheat could varybetween
farms, duetotheoccurrence ofgrassy strips(farms T,L,S,E,I,J),asterilestrip (H),a
recently drilled flower strip(F)oratransport track (O).Samplingwasdoneonce,inthe
periodfromthe7thofJuneuntilthe6thofJuly, following themethods ofReddersen (1997)
andMoreby &Sotherton (1997).
Vegetation dwelling arthropods werecollectedbymeansofavacuum sampler(ES2100,
EchoLakeZurich,U.S.A.) for 120sineach 1 m sampling area.Theairflow ofthissampler
was 8.5 m3inasampling areaof0.01m2,whichcorresponds totheair flow ofthe apparatus
recommended byMacLeod etal.(1995).Anet (pore size:0.8x0.8 mm 2 ) wasinserted inthe
suctiontube.Asquareof 1 m2areaand0.4mhigh,madeoffour multiplex boards,was
placed inthevegetation before switching onthe sampler.
Thesampleswereput inaplasticbag,transported inacoolbox and stored inadeepfreeze
(-20 °C).Sampleswerecleaned inthelaboratory. Litterwasremoved and soilwaswashed
awaywithwater inasieve (pore size: 1x1 mm2).Slugs andsnails (Gastropoda) and
springtails (Collembola)werediscardedbecausevacuum sampling isnot effective for
quantification ofthesegroups(Potts &Vickermann, 1974).Arthropodswere stored in95%
alcohol.Individuals weresortedtotaxaatorder-or family-level andplaced into five different
arthropod functional groups:
- Detritivores,includingmainly adult dipterathathavedetritivorous larvae,andwoodlice
(Isopoda);
- K-orsenescense feeding herbivores (White, 1978)that feed onmatureplant tissueswith
highC/N ratios andtendtohave aslowerdevelopment, largerbody size(Crawley, 1983)
anddefensive traits(Power etal.,1996).Herbivores which areanimportant constituent of
'chickfood' for farmland birds (Moreby etal, 1994),likesawflies, lepidopteran larvae,
hoppers,bugs,leafbeetles,weevils andgrasshoppersbelong tothisgroup;
- r-orflushfeeding herbivores (White, 1978)that feed onyoungtissueswith lowC/Nratios
and lowfibrecontent (White, 1978).Theygenerally have asmallbody size, fast
development andgood dispersal abilities.Forreasonsofsimplicity,r-herbivores were
10
representedbyonlyAphididae; infew available studiesonorganiccrop communities
(Kromp&Meindl, 1997),aphidscorresponded most clearlytothe definition;
- Predators includingbothpolyphagous andoligophagous species;
- Parasitoids, almost exclusively represented byParasitica (Hymenoptera).
Extraefforts weremadetoidentify Dipteratothe family-level (key:Unwin, 1981)because
Dipteraoccurred inlargenumbers andinvolved largeproportions ofallthreedetritivores,
herbivores andpredators (Frouz, 1999;Weberetal.,1997).
2.2.2.Crop andE.I.-vegetation
Ineach 1 m2plot"inwheat fields, visual estimationsweremadeofcropcover {i.e.%coverof
soil surface byverticalprojection) andunder storyvegetation cover. Theunder storyincluded
arableweeds and/orundersown grass(Loliumperenne) and/orclovers (Trifoliumpratenseor
T. repens).Thespecies oftheunder storywerelisted.Ineach 1 m2plot intheE.I.,the
vegetation coverwasestimated visually and specieswerelisted.Plant speciesnumberof
understory andE.I.vegetation were calculated for eachplot.
2.2.3.Farmmanagementandlayout
A 1:5000mapwasmadeofeach farm, depictingthedifferent crops andthe ecological
infrastructure (E.I.)-Onthesemapstheareaofsemi-natural andcrophabitatsweremeasured.
The'E.I.-area'wascalculated asthepercentage ofsemi-naturalhabitat ofthefarm area
(without the farm yard).Farmrotation intensitywasdefined astheproportion of gramineous
crops(cereals and leypasture) ofthetotal croparea.Thespatial arrangement oftheE.I.or
'E.I.density',was expressedbythepercentage ofthefarm which liedwithin 100mdistance
oftheE.I.Incasethecanalbankvegetation wascutbothafter September 15th aswellas
before May 15th,adistanceof70mwasconsidered. Theinfluence offieldmarginsonthe
abundance oflargecarabidbeetles and spidersprobably doesnot exceed 70-100m(Booij,
unpublished data).
Dataontheyearofconversion ofthewhole farm toorganichusbandrypractices inthewheat
cropin 1998,andmowing ofcanalbanks andgrass stripswereobtained usinga
questionnaire. Themowingmanagement isrepresented bythemonthofthefirst cut,because
thiscut largelydetermines thephenological stage ofthevegetation inJune andJuly.
2.3.Statisticalanalyses
Allmeasurements weretested fornormality and '°log-transformed. All subsequent analyses
were conducted using Statistical Analysis System (SASInstitute, Cary,North Carolina).
2.3.1.Discriminantanalyses
Individual farms wereclassified intooneofthreegroups onthebasisof corresponding
characteristics (Table 1).For analysis ofdata from crop areasamples (234m2),the
classifications werebased onrelevant farm structure characteristics (duration, E.I.-area and
rotation intensity) oroncropperformance characteristics (crop cover,under story coverand
under story speciesnumber).For analysisofdata from E.I.samples (117m ),the
classifications werebased onrelevant farm structure characteristics (E.I.-area andduration)or
onvegetation performance characteristics (month offirst cut,E.I.-vegetation coverorplant
species numberperm2).
Farmswere classified accordingtotwo splits:thefirstsplitbased ononeofthe above
mentioned characteristics separated acategory of 3-7 farms, andthesecond splitbasedon
another ofthesecharacteristics divided theremaining 6-10farms inasecond andathird
category. Theminimum category sizewas3farms. Forallobtained classifications canonical
discriminant analyseswereperformed onthenumbersofarthropodsineachfunctional group.
11
Observations inthewheat andintheE.I.wereanalysed separately for crop areaandE.I.
classifications, respectively. Classifications withthehighest Wilks'LambdaF-valuewere
selected;thisselection yielded thefour best classifications.
Stepwisediscriminant analyseswereperformed onthenumbersofarthropods ineach
functional group todetermine themost important groupsthat couldclassify the farms intothe
threecategories.Arthropod observations inthecropareaandintheE.I.wereagain analysed
separately. Canonical discriminant analysiswasusedtodeterminethemagnitudeand
direction oftheassociation ofindividual variableswith indicatorvariables. Standardised
canonical coefficients largerthan 0.3dividedbythesquareroot oftheeigenvalue ofthe
canonical function (Afifi &Clark, 1984)wereconsidered largeenoughto contribute
significantly tothe classification.
2.3.2.Taxa differentiatingamongfarm categories anddistancefrom E.I.
Differences inspeciescomposition wereexpressed bythetaxathathad significantly higheror
lowernumbers inonecategory ascompared totheothercategories.Differences in abundance
ofvarioustaxabetweenthethreecategoriesinthe four selected classifications weretestedby
ANOVA (P<0.05),including aDuncan'smultiplerangetest.Inthistest non-transformed data
wereused, andtaxathatoccurred withlessthan20individuals inthewholedata-set were
omitted.Differences inabundance oftaxaamongthe sampling distances from theE.I.of0m
(intheE.I.), 10m(inwheat) and 30m(inwheat)were alsotestedwithANOVA (P<0.05)
includingDuncan'smultiplerangetest.
2.3.3.Differencesinspecies diversity
Differences inspeciesdiversitywerealsoanalysed. Taxathatoccurred with lessthan20
individuals inthewholedatasetwereomitted. Parasitoids andr-herbivores werenot
consideredbecausebothgroups included onetaxon.Observations inthecroparea(234m2;
pooled samplesof 10and 30mfrom theE.I.) andintheE.I.(117m2)were analysed
separately. Calculationsweremadeofthenumber oftaxaperarthropod functional groupper
m (speciesdensity: S)andtheMargalefdiversity indexperm2(Dm=(S-l)/lnN: S=number
of species,andN=number ofindividuals) (Magurran, 1988).Differences in SandDmamong
thethreecategories ineachofthe four selected classifications weretestedbyANOVA
(P<0.01),includingDuncan'smultiple rangetest.Differences in SandDm amongthe
samplingdistances (0, 10,and30mfrom theE.I.)were alsotestedbyANOVA(P<0.01),
includingDuncan'smultiplerangetest,usingthewholedata-set (351m2).
2.3.4.Gradientanalysis
Thepooled data-set ofwheat andE.I. samples (351m2)wasused to analysethe distribution
ofarthropod functional groups alongthegradient from E.I.tocrop centre,represented by
threesampling distances0m(E.I.), 10m(wheat) en30m(wheat),for each farm category.
Linearregressions (GLM;P<0.1)wereperformed forthe four selected classifications using
10
log-transformed data.Effects ofdistance,category, anddistancebycategory interaction
weretested. Cropareaobservations (234m2) andE.I.observations (117m2)werealsotested
separately for differences between categories inthefour selected classifications (GLM;
P<0.1),includingDuncan'smultiplerangetest.
12
3. Results
3.1. Observednumbers ofepigeic arthropodfunctionalgroups
Atotal of26,722organismswerecaught in351m2sampling areaincluding 12,346aphids.
Onaverage,63%and 13%ofvegetation dwelling arthropod numberswere aphidsinthecrop
areaandintheecological infrastructure, respectively.Average arthropod density inthecrop
area, excluding aphids,was28organisms/m2 ofwhichthemost abundant taxa(>2%)were:
herbivores:leafbeetles (Chrysomelidae)(6%) andhoppers(Cicadellidae)(5%);detritivores:
chironomidmidges(12%)andsciaridmidges(4%); predators:spiders(10%),empidid flies
(9%), anddolichopid flies (3%);andparasitoids (32%)(Table2a).Theaveragedensityinthe
E.I.,excluding aphids,was67organisms/m withthemost abundant taxa (>2%)being:
herbivores:hoppers(36%),chloropid flies (7%),andbugs(3%);detritivores:wood lice(7%)
andchironimidmidges(5%);predators:spiders (9%)andants(3%);andparasitoids (7%)
(Table2b).
Table2a
Thetotal number/18 m~perform ofarthropod taxa inthewheat cropcaptured by vacuum sampling.
Taxa
Isopoda
Chironomidae
Mycetophilidae
Sciaridae
Lonchopteridae
Phoridae
Borboridae
Drosophilidae
Sepsidae
Cicadelidae
Heteroptera, herbivores
Chrysomelidae
Curculionidae
Tipulidae
Chloropidae
Opomyzidae
Ephidridae
Symphyta
Heteroptera, predator
Coccinellidae
Cantharidae
Chrysopidae
Syrphidae
Empididae
Dolochopodidae
Aranae
Carabidae
Staphylinidae
Formicidae
Parasitica
Aphididae
Funct.
Farm
R
group
T
F
K
Z
L
detr
0
0
0
0
0
0
dea22
8
67
92
34
26
den2
0
1
3
9
2
detr
4
12
10
18
10
6
dea1
0
2
3
0
43
den
1
0
1
0
2
0
dea1
1
0
1
3
0
den20
30
1
20
4
1
detr
0
0
0
1
1
0
K-herb
0
2
18
5
8
5
K-herb
1
2
0
1
0
1
K-herb
26
6
30
13
29
58
K-herb
0
0
0
0
0
1
K-herb
0
0
1
1
6
0
K-herb
5
1
2
2
23
4
K-herb
1
0
0
0
1
2
K-herb
6
1
6
6
23
7
4
K-herb
1
0
0
1
2
pred
0
1
1
0
0
1
pred
14
1
7
0
30
8
pred
12
18
12
18
12
10
pred
0
2
2
2
0
0
pred
20
0
28
3
36
26
pred
7
22
27
12
23
25
pred
0
7
1
1
6
0
pred
7
10
62
21
72
27
pred
0
0
1
0
0
0
pred
1
2
2
0
3
5
pred
0
2
0
0
0
0
par
117
68 140 183 311 336
r-herb 4693 270 1284 1437 746 701
13
B
J
M
H
O
S
E
0
1
0
0
0
1
0
11
60
10
52
11
20 380
1
2
7
10
1
20
7
22
65
4
23
12
2
61
0
14
1
5
0
3
0
0
0
1
2
2
3
0
3
2
7
5
1
20
10
1
9
0
18
0
3
3
0
1
0
8
23
0
1
41
59
30
80
30
11
8
1
0
0
0
0
0
0
62
8
32
13
51
65
8
1
0
0
4
0
0
51
0
0
5
0
0
0
1
14
0
9
2
2
3
8
0
1
1
0
1
0
1
2
1
0
1
0
0
0
0
1
0
0
0
2
3
1
1
0
0
0
2
2
10
1
3
3
11
3
5
4
3
4
2
14
5
0
4
7
11
6
0
1
6
1
7
1
4
3
18
8
17 173 139
13
68
44
29
12
14
5
0 103
30
3
57
42
15 189
20
81
61
16
1
0
10
1
3
5
4
3
2
2
6
5
3
0
0
0
0
1
2
0
67 143
28 118 251 238
58
82 397 290 188 236 367 465
Table2b
Totalnumber/9 m~perform of arthropod taxa inthe ecological infrastructure captured by vacuumsampling.
Taxa
Isopoda
Chironomidae
Mycetophilidae
Sciaridae
Lonchopteridae
Phoridae
Borboridae
Drosophilidae
Sepsidae
Cicadelidae
Heteroptera
Chrysomelidae
Curculionidae
Tipulidae
Chloropidae
Opomyzidae
Ephidridae
Symphyta
Heteroptera
Coccinellidae
Cantharidae
Chrysopidae
Syrphidae
Empididae
Dolochopodidae
Aranae
Carabidae
Staphylinidae
Formicidae
Parasitica
Aphididae
Funct.
Farm
group
T
detr
28
detr
220
detr
1
16
deaden16
detr
4
detr
48
detr
34
detr
17
K-herb
388
2
K-herb
1
K-herb
1
K-herb
6
K-herb
K-herb
16
K-herb
25
K-herb
7
K-herb
4
9
pred
pred
4
pred
17
4
pred
pred
2
pred
41
1
pred
pred
76
pred
19
pred
7
pred
49
par
88
r-herb
488
F
61
0
0
0
0
0
3
1
1
58
2
0
0
4
3
0
0
1
0
0
4
1
0
4
0
34
6
2
49
14
11
K
12
2
0
2
15
0
3
6
2
8
0
3
0
1
2
2
2
0
2
2
4
0
0
21
1
31
11
6
65
27
45
Z
13
18
1
13
1
12
5
12
3
211
54
0
0
3
29
11
14
13
22
0
26
0
0
1
3
86
6
2
7
95
106
R
0
2
0
5
2
7
16
7
3
772
1
0
0
0
36
9
7
1
3
0
0
0
0
4
6
83
4
1
19
49
127
L
364
32
1
5
9
0
16
8
2
190
142
1
3
4
12
5
29
6
91
0
10
1
0
9
4
116
14
29
36
47
59
H
1
0
0
2
1
3
4
6
1
105
1
0
0
0
125
0
0
1
0
0
0
0
1
1
0
8
3
5
6
8
4
B
O
1
0
3
3
1
1
18
47
1
0
7
6
4
2
6
10
1
3
311 496
0
0
1
0
0
0
1
1
55 104
3
1
1
2
6
1
13
0
0
1
0
1
0
1
0
0
1
1
11
1
32
31
1
1
0
0
0
5
48
59
98
35
S
13
126
2
4
6
1
10
5
2
76
1
0
1
1
27
5
3
1
11
0
0
1
1
13
10
82
16
3
6
68
10
3.2.Crop areaarthropodfunctional groupsandspecies diversity
3.2.1.Arthropodfunctional groupsaffectingdistinctions amongfarm structure categories
Theclassification 'dur/int'basedonorganic farming duration (first split) androtation intensity
(second split)gavethebest separation oftheobservations (canonical discriminant analysis,
Wilks'Lambda,F-value=18.7, PO.0001; Table3).Category 1included therecently
converted organic farms; category2included thelongduration (>6years) organic farms with
anintensivecroprotation (<33% gramineous crops);category 3included long duration
organic farms with anextensive croprotation. Classifications based ondifference in
percentage E.I.('area')showed lessdistinction thanclassifications basedonduration and
rotation intensity (Table3).
Theseparation intoduration-intensity categories,based onarthropod functional group
numbers inwheat, isillustrated inaplot ofcanonical variabletwoversus canonical variable
one(Fig.2).All arthropod functional groupswere selected asimportant factors by stepwise
discriminant analysis fordiscrimination amongthethreecategories (Table4).Thefirst
14
J
12
0
0
1
2
5
1
0
12
94
7
0
2
0
72
1
1
0
9
5
0
0
0
7
2
57
4
6
5
30
82
E
26
14
0
5
17
1
26
1
4
66
36
0
0
0
35
1
1
2
5
1
1
5
1
21
2
43
2
1
2
35
35
M
0
1
0
2
0
0
2
0
6
32
1
0
0
0
14
0
1
0
6
6
0
0
1
12
3
15
0
1
1
6
90
canonical function containing all arthropod functional groups,separated theorganic extensive
croprotationcategory from bothothercategories (Fig.2).r-Herbivores,predators andKherbivores werepositively associatedwithrecent conversion ororganicintensivecrop
rotation,whereasdetritivores andparasitoidswerepositively associated with organic
extensive croprotation (Table4).Thesecond canonical function, determined mainlyby
predators andr-herbivores separated longduration intensive farms from recently converted
farms;predatorswereassociated withrecently converted farms andr-herbivores with
intensive farms.
K-herbivoresandpredatorswere>25%more abundant onaverage,inrecently converted
farms (category 1)than intheothertwocategories.Detritivores andparasitoidswere
respectively >40%and>10%more abundant inorganic extensive farms (category 3)thanin
theotherthetwocategories.r-Herbivores weremost abundant inintensive organic farms
(category 2)andhadintermediate numbersinrecently converted farms ascompared to
organic extensive farms (Table4).
Table3
Examples of classifications of the crop area and theecological infrastructure, including the the Wilks'Lambda
F-value and thesquared canonical correlation obtained by canonical discriminant analysis. Abbreviations of
category characteristics areexplained in Table I.
category
farms
category
farms
category
farms
Category1
dur<6
HZBREM
dur<6
HZBREM
int>33
FOSEM
Category 2
dur>6 & int<33
TKLJ
dur>6&area<2.1
FKO
int<33 &dur>6
TKU
Category 3
dur>6 & int>33
FOS
dur>6& area>2.1
TLSJ
int<33 & dur<6
HZBR
category
farms
category
farms
category
farms
ccov>85
BME
ccov>85
BME
usp>3.5
OREJ
ccov<85 & ucov>7.6
TKRL
ccov<85 & usp>3.5
ORJ
usp<3.5 & ucov>7.6
TKL
ccov<85 & ucov<7.6
FOHZSJ
ccov<85 & usp<3.5
TFKHZLS
usp<3.5 &ucov<7.6
FHZBMS
Ecological Infrastructure
Farm structure
category
farms
categories
category
farms
Category 1
area>2.1
TLSEJ
dur<6
HBZRME
Category 2
area<2.1 &dur>6
FKO
dur>6& area<2.1
FKO
Category 3
area<2.1 & dur<6
HZBRM
dur>6& area>2.1
TLSJ
E.I. vegetation
performance
categories
mow>7
TLSE
mow>7
TLSE
Eicov<80
FKRM
mow<7 & eicov>80
HZBOJ
mow<7 & eisp>4,3
BOMJ
eicov>80 & eisp<4.3
THZ
mow<7 & eicov<80
FKRM
mow<7 & eisp<4,3
FKHZR
eicov>80 & eisp>4.3
BOLSEJ
Crop area
Farm structure
categories
Crop performance
categories
category
farms
category
farms
category
farms
15
F-value Sq.Can.
18.7
0.37
8.66
0.23
7.54
0.26
38.32
0.56
25.1
0.54
14.09
0.34
7.84
0.39
6.53
0.34
15.94
0.48
10.53
0.51
6.8
0.37
3H
2
1
0
• no
-1
-2 H
-3
•1
0
can1
Fig. 2.Plotof thesecond and first canonicalfunctions discriminating amongfarm categories of the
classification 'int/area'.Squares representfarms with >-40%gramineous crops; circles representfarms with<
40%gramineous crops and >2.2%E.I. area; triangles representfarms with >40%gramineous crops and
<2.2%E.I.
-1
0
can1
Fig. 3.Plot of thesecond andfirstcanonicalfunctions discriminating amongfarm categories of the
classification 'int/area'. Circlesrepresentfarms withdense crops (>85%); triangles representfarms with sparse
crops (<85%) including an understory >7.6%; squares representfarms with asparse crop including apoor
understory (<7.6%).
16
Table4
Arthropod variables that contributed significantly to theclassification of thecrop area observations in the three
farm categories bystepwise and canonical discriminant analyses,standardised canonical coefficients, and mean
valuesper crop area category. Classification in 'dur/int'-categories isbased onfarm structure characteristics
and theclassification 'ccov/ucov'-categories isbased oncropperformance characteristics. Theabbreviations of
thecategory characteristics are explained in Table1. Comparisonof arthropod mean numbers in thecategories
according toDuncan's multiple range test.
Canlb
Farm structure
(dur/int)
Variablesa
r-Herbivores
Predators
Detritivores
K-herbivores
Parasitoids
Standardised Category 1
coefficient dur<6
0.95 c
0.46
-0.62
0.67
-0.49
Canld
Crop
performance
(ccov/ucov)
Variables *
Predators
r-Herbivores
Detritivores
K-herbivores
Parasitoids
Mean values andmultiple range comparison
mean
32
13
5
5
8
b
a
ab
a
b
Category
dur>6&
int>33
mean
14
5
10
3
10
3
c
b
a
b
a
(PO.001)
(PO.001)
(P<0.07)
(PO.001)
(P<0.05)
Mean values andmultiple range comparison
Standardised Category 1
coefficient ccov>85
1.15 e
0.54
-0.15
0.52
-0.44
Category 2
dur>6&
int<33
mean
96 a
6 b
4 b
4 a
9 ab
mean
20
23
7
7
6
a
b
a
a
b
Category 2
ccov<85&
ucov>7.6
mean
7 b
103 a
5 a
4 b
13 a
Category 3
ccov<85&
ucov<7.6
mean
5 c
23 c
6 b
3 c
8 b
(PO.001)
(PO.001)
(PO.05)
(PO.001)
(PO.001)
*Variables are listed in order ofselection by stepwise discriminant analysis.
Canonical function 1;responsible for 71% ofthe variation.
c
Standardized coefficients >0.39 were considered large enough for interpretation.
Canonical function 1;responsible for 73%of the variation.
e
Standardized coefficients >0.26 were considered large enough for interpretation.
3.2.2. Differencesinspeciesdiversityamongfarm structurecategories
Recently converted andintensive longduration farms had similar speciesrichnessinall
functional groupsconsidered (detritivores,K-herbivores, andpredators).The species
diversitieswereonlysimilar for K-herbivores andtotaltaxa(Table 5).Detritivoresweremost
diverseinrecentlyconverted farms. Thereweretwodifferentiating taxa:Phoridae
(detritivorous flies) preferred recently converted farms andherbivorousbugs (Heteroptera)
preferred longduration intensive farms.
3.2.3. Arthropodfunctional groupsaffectingdistinctions amongcropperformancecategories
Itwasenvisaged thatcropperformance factors couldoffset farm structure factors in
determining arthropod functional group assemblages.Thisproved tobe correct:
theclassification 'ccov/ucov'basedoncropcover(first split)andweedcover (second split)
provided thebest separation ofobservations (Wilks'Lambda,F-value=38.3, P<0.0001;
Table3).Cropperformance category 1 included densecropstands (cover>85%);crop
performance category2included relatively sparsecropstands (cover<85%),accompanied by
17
anunderstoryvegetation (>7.6%cover);cropperformance category 3included relatively
sparsecropstandswhichhad apoorunderstory vegetation.
Theseparation ofcrop-weed covercategories,based onarthropod functional groupnumbers
inwheat, isillustrated inaplotofcanonicalvariabletwoversuscanonical variableone(Fig.
3).Allarthropod functional groupswere selected asimportant factors by stepwise
discriminant analysis for discrimination amongthethreecategories (Table4). Extremeswere
densecrops andsparsecropswithpoorunder story(Fig.3).Significant contributions tothe
first canonical function werethepositive associations ofpredators,r-and K-herbivores with
densecrops,andthenegative association ofparasitoidswithdensecrops(Table4).The
relationbetween understoryvegetation and arthropod groupswasnot aspronounced: the
categoryof sparsecropswithunder storywasseparated from both other categoriesbythe
secondcanonical function, determined significantly bypredators (negative association) andrherbivores (positiveassociation).
K-herbivores andpredatorsindensecrops(category 1)wererespectively >65%and>40%
moreabundant onaverage,thanintheothercategories.r-Herbivores andparasitoids in sparse
cropswithunderstorywererespectively>75% and>40%moreabundant thaninthetwo
othercategories (Table4).
3.2.4. Differencesinspeciesdiversityamongcropperformancecategories
Speciesrichnesswasgenerally highestwhencropcoverwasmorethan 85%.Diversityof
senescense-feeding herbivores,predatorsanddetritivores was lowest inthecategoryof sparse
cropswithpoorunderstory ascompared totheothercategories.Densecropshadthehighest
diversityofdetritivores.Densecrops andsparsecropswithunder storyhad asimilar diversity
ofK-herbivores. Sparsecropswithunder storyhad thehighest diversity ofpredators (Table
5).
Thirteentaxahad significantly higherdensitiesinoneortwo ofthe crop performance
categories (ANOVADuncan,P<0.05):indensecropsthehighest densitieswereobserved for
woodlice (Isopoda, detritivore),Phoridae,Borboridae, Sepsidae (alldetritivorousdiptera),
Cicadellidae (herbivore),Aranae,Carabidae (polyphagous predators), and Dolichopodidae,
Empididae (predacious flies); insparsecropswithunder storythehighest densities occurred
amongDrosophilidae (detritivorous fly),herbivorousbugs (Heteroptera), Ephydridae
(herbivorous fly), andhooverfly larvae(Syrphidae;predacious fly).
3.3.EcologicalInfrastructurearthropodfunctional groupsandspecies diversity
3.3.1.Arthropodfunctional groupsaffectingdistinctionsamongfarm structurecategories
Oftwoconsideredpossibilities theclassification area/dur,based onE.I.areaasfirst splitand
farm organicduration assecond split gavethebest separation ofobservations (canonical
discriminant analysis,Wilks'Lambda,F-value=7.84,P<0.0001;Table3).Farm structure
category 1 included farms withanenlarged E.I. (>2.1%ofthefarm arablearea)and
corresponded to'improved E.I.';theothertwocategories arefarms with asmallE.I.which
couldbe longduration organic farms thatdidnot enlargetheE.I.area(category 2)orrecently
converted organic farms (category3).
Theseparation into area-duration categories,based onarthropod functional groupnumbersin
theE.I.,isillustrated inaplotofcanonicalvariabletwoversuscanonical variableone(Fig.
4).Detritivores andK-herbivores wereselected asimportant factors bystepwise discriminant
Table5
Comparison between the threecategories inallfour selected classifications, withregard to their species
richness (S)andMargate/diversity index (DJ (GLM;significance level *=P<0.1; **P<0.01; ***P<0.001);
detr = detritivores; K-herb= senescensefeeding folivores; pred =predators; total =detritivores, K-herbivores
andpredators. Abbreviations of category characteristics areexplained in Table I.
Crop area
Farm structure
categories
Crop
performance
Categories
dur<6
dur>6 &int<33
dur>6 & int>33
Significance
ccov>85
ccov<85&ucov>7.6
ccov<85&ucov<7.6
Significance
S
detr
2.3
1.9
1.5
a
a
b
***
2.7
2.1
1.5
Dm
detr
1.0
0.7
0.6
a
b
b
S
K-herb
2.1 a
1.8 a
1.1 b
a
b
b
2.4
2.0
1.2
***
a
b
c
1.0
0.7
0.7
***
Dm
K-herb
0.8 a
0.8 a
0.4 b
***
a
b
c
0.8
0.8
0.5
a
a
b
S
pred
3.4 a
3.1 a
2.4 b
Dm
pred
1.2 b
1.3 a
1.1 b
S
Total
7.8 a
6.8 b
5.0 c
***
*
***
7.0
3.4
2.4
a
b
c
1.2
1.4
1.1
b
a
b
9.1 a
7.5 b
5.0 c
Dm
Total
2.3 a
2.3 a
1.7 b
**#
2.4
2.4
1.8
a
a
b
***
**
#**
***
***
***
***
***
S
detr
4.1
2.5
2.4
Dm
detr
1.2
1.1
1.3
NS
1.2
1.3
1.1
NS
S
K-herb
3.8 a
2.0 c
3.0 b
Dm
K-herb
0.9 a
0.7 b
0.6 ab
S
pred
4.8 a
3.2 b
2.8 b
Dm
pred
1.4 a
1.0 b
1.0 b
S
Total
12.8 a
7.7 b
8.2 b
Dm
Total
2.9 a
2.0 b
2.0 b
***
**
***
***
13.8 a
8.5 b
7.2 b
3.0
2.0
2.0
***
***
Ecological Infrastructure
Farm structure
E.I. vegetation
performance
Categories
area>2.1
area<2.1 &dur>6
area<2.1 &dur<6
Significance
mow>7
mow<7 & eicov>80
mow<7 & eicov<80
Significance
a
b
b
***
4.7
2.7
2.0
***
a
b
b
***
4.0
3.2
2.0
***
*
a
b
c
0.9
0.6
0.7
**
a
b
b
5.1
2.6
3.6
***
a
c
b
1.4
0.9
1.2
a
c
b
***
analysis for discrimination amongthethreecategories(Table6).Thelargest differences in
arthropod functional groupcompositionwerebetweentheenlarged E.I. category andrecently
converted farm category (Fig.4).Inthe first canonical function detritivoreswerepositively
associated andK-herbivores negatively associatedwith enlarged E.I.(Table6).Althoughthe
predator numberwassignificantly higherintheenlarged E.I. category ascomparedtothe
othercategories (Table 6),ithad littlecanonicalpowerinthefirst canonical function because
ofahighcorrelation (Pearsoncorrelation coefficient =0.79;P<0.01)between detritivore and
predator abundance.Thesecondcanonical function, determined byK-herbivores (positive
association), separatedbothextremecategories from thethirdcategoryoflongorganic
duration farms with smallE.I.
Detritivores andpredatorswere>70%and>40%moreabundant onaverageinthe enlarged
E.I.category (1)ascompared tothesmallE.I. categories.K-herbivores were>20%more
abundant onaverageinrecently converted farms (category 3)than intheother categories
(Table6).
3.3.2. Differencesinspeciesdiversityamongfarm structure categories
SpeciesrichnessofK-herbivores anddetritivores anddiversity ofpredators andtotaltaxa
were significantly higherintheenlarged E.I.categorythaninothercategories (Table 5).The
onlydifferentiating taxawereweevils(Curculionidae;K-herbivore) whichpreferred enlarged
E.I.
19
a
b
b
3.3.3. Arthropodfunctional groupsaffectingdistinctions amongE.I. vegetationperformance
categories
Theclassification 'mow/eicov'basedon first mowing date(first split)and E.I. vegetation
cover(second split)gavethebest separation ofobservations (canonical discriminant analysis,
Wilks'Lambda,F-value=15.94,PO.0001; Table 3).Vegetation performance category1
included E.I.whichwascut late (after July 1st) and included the'improved E.I.'ofthethree
prototype farms andtheorganic experimental farm (E).Ecological infrastructure whichwas
cutbefore July couldhave ahighvegetation cover(>80%)(category 2)oran 'open vegetation'
i.e.alowcover(<80%) (category 3).Wedefined category2as'grassy E.I.'becauseearly
mowing inMay,combined with ahighermowing frequency peryearand/or careful mowing
resulted inastable,dense sward dominated byperennial grassspecies.
Table6
Arthropod variables that contributed significantly tothe classification of theE.I. observations in the threefarm
categories bystepwise and canonical discriminant analyses,standardised canonical coefficients, andmean
valuesper crop area category. Classification in 'area/dur'-categories isbased onfarm structure characteristics
and theclassification 'mow/eicov'-categories isbased on vegetationperformance characteristics. The
abbreviations of thecategory characteristics are explained in Table I. Comparison of arthropod mean numbers
inthecategories according toDuncan's multiple rangetest.
Canlb
Mean values andmultiple range comparison
Farm structure
(area/dur)
Standardised Category 1
Category 2
Category 3
coefficient
area>2.1
rea<2.1 &
area<2.l &
dur>6
dur<6
mean
mean
Variables a
mean
26 a
4 c
Detritivores
1.16c
7 b
-0.49
32 a
41 a
K-herbivores
26 b
-0.18
21 a
11 b
9 b
Predators
Parasitoids
0.33
6 a
4 b
5 b
0.03
13 a
8 a
r-Herbivores
6 a
Canld
E.I. vegetation
performance
(mow/eicov)
Variables *
Detritivores
K-herbivores
Predators
Parasitoids
r-Herbivores
Mean values and multiple
Standardised Category 1
coefficient
mow>7
1.34e
-0.26
0.16
0.11
-0.22
mean
31
35
23
7
14
a
a
a
a
a
Category 2
mow<7&
eicov>80
mean
6 b
40 a
9 c
5 a
7 a
(PO.001)
(PO.01)
(PO.001)
(PO.05)
NS
range comparison
Category 3
mow<7&
eicov<80
mean
5 b
27 b
12 b
3 b
8 a
(PO.001)
(PO.001)
(PO.001)
(PO.001)
NS
"Variables arelisted in order of selection by stepwise discriminant analysis. The italicised variables were not
selected by stepwise discriminant analysis.
b
Canonical function 1:responsible for 85%ofthe variation.
c
Standardised coefficients >0.37 were considered large enough for interpretation.
Canonical function 1:responsible for 63%ofthe variation.
"Standardised coefficients >0.31were considered large enough for interpretation.
20
3
2
l H
A 4A
%
, - , • * § *
•
-,• o
*,°A
& * A
DA A
^» A A " **
AflD
A /A 0
A
&*
•1
H
AA%
a
D
oA2°
D
0
-2
oo
-3
-4
-2
-1
can1
Fig. 4.Plotof thesecond andfirstcanonicalfunctions discriminating among E.I.categories of the classification
'area/dur'. Trianglesrepresent enlargedE.I.(>2.1%);circles representsmall E.I. onfarms witha long organic
duration; squares represent smallE.I.onfarms withashort organic duration.
0
31
2-
0
o
o°
°o
8
0
0
o
1-
A°
o
o
o
01
0
$>
A
-2 -
O
A
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o
O°T> A
0$
A
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A A
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A
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i
A A
A
•
-r
—
D
A
A
A
-3 -
n
tP<*
^
A
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can1
-1
Fig. 5.Plot of thesecond and first canonicalfunctions discriminating among E.I. categories of the classification
'eispn/eicov'.Squares represent late mownE.I.; circles represent earlymown E.I. withdense vegetation;
triangles represent early mownE.I.withsparse vegetation.
21
Theseparation into'mow-eicov'categories,based onarthropod functional group numbersin
theE.I.,isillustrated inaplotofcanonicalvariabletwoversuscanonical variableone(Fig.
5).All arthropod functional groupswere selected asimportant factors by stepwise
discriminant analysis for discrimination amongthethreecategories (Table6).Thefirst
canonical function containingonly detritivores,separated latemowing category from grassy
E.I.andopenvegetation categories (Fig.5).Detritivores areassociatedpositivelywith late
mowing(Table6).Althoughthepredatornumberwassignificantly higherinthelatemown
E.I.categoryascomparedtotheothercategories (Table6),ithad littlecanonicalpower inthe
firstcanonical function becauseofahighcorrelation betweendetritivore andpredator
abundanceintheE.I.Thesecond canonical function, determined mainlybyK-herbivores and
parasitoids (bothpositively associated) andpredators (negatively associated) showeda
separationbetween grassyE.I.(category 2)andopenvegetation (category 3).All functional
groups,except theK-herbivores wereonaveragemore abundant inthelatemownE.I.
category (1)ascomparedtoboth othercategories:detritivores andpredators were
respectively >80%and>40%more abundant. K-herbivores were>10%more abundanton
averageingrassyE.I.(category 2)thaninboththeothercategories (Table6).
3.3.4. DifferencesinspeciesdiversityamongE.I. vegetationperformancecategories
Speciesrichnessanddiversity ofallarthropod functional groups,except diversity ofdetritivores,weresignificantly higher inlatemownE.I.thaninothercategories.Thecategoryof
grassy E.I.hadthe lowest diversity ofpredatorsascompared totheothercategories (Table5).
Ofthetotalofeight differentiating species,sixpreferred latemownE.I.:three detritivorous
taxa(Chironomidae, Lonchopteridae, Borboridae) andthreepredacious taxa (Chrysopidae,
Carabidae,andEmpididae).Thehigh abundance ofchloropid flies (herbivorous) andphorid
flies(detritivorous) wastypical for thecategory ofgrassyE.I. vegetation.
3.4. Arthropodfunctional groupsalongthegradientfrom E.I.tocrop
3.4.1.Functionalgroupcomposition alongE.I. - cropgradients
Itwasexpected thattherelationsbetween abundance ofvarious functional groupsand
distance from theE.I.wouldbe similar for different farm categories.However, therewere
significant interactions betweencategories inall four selected classifications and distance
from theE.I.,withregardtoabundance ofdetritivores andpredators.Therewere also
significant interactionsbetween categories anddistancewithregard toK-herbivores for some
classifications butnot for others.Theinteractionswerestrongest forpredator distributions,
particularly for crop areaclassifications but alsofor 'mow/eicov' classifications. These
interactions arebest illustrated fortheE.I.classification 'mow/eicov' (Fig.6).Although in
most farms abundance ofpredators anddetritivores werelowest at30mdistance from the
E.I., farms with an earlymowing date andrelatively littleplant coverinthe E.I.(category3)
hadmorepredators anddetritivores at 30mthan at 10mdistancefromtheE.I.(Fig.6aand
c).Thus,highdensities intheE.I.donot always gohand-in-hand withhigh densities inthe
adjacent crop.
Despitethesignificant interactions,predators,K-herbivores, anddetritivores were generally
most abundant intheE.I.andwerelowerinthewheat field (Fig.6a,b,c). Although
abundanceweregenerally decreasing orsimilarwith increasing distance from theE.I.,in
category 3theywere sometimeshigher at30mthan at 10minsidethewheat field (Fig.6
a,b,c).Ontheotherhand, abundance ofparasitoids andr-herbivores weregenerally lowestin
theE.I.andhighest at30minsidethewheatfield(Fig.6d,e),withtheexception ofthe
parasitoids incategory2(grassyE.I.) thatwerehighest at 10minsidethewheat field and
lowerintheE.I.and at30minsidethewheatfield(Fig.6d).
22
3.4.2. DifferencesindiversitybetweenE.I. andcrop area
Speciesrichnessofdetritivores,K-herbivores andpredatorswassignificantly higherinthe
E.I.,but diversity (Margalef) was onlylargerfor detritivores.Tenof30consideredtaxaof
predators,K-herbivores anddetritivores showed apreference for E.I.:Phoridae,Borboridae,
Cicadellidae, Chloropidae, Opomyzidae,Symphyta,predacious Heteroptera,Aranae,
Carabidae, andFormicidae.Twotaxa showed apreference for thecrop area:Chrysomelidae
(herbivorous) and Syrphidae (predacious).Noneoftheconsidered taxahad a significantly
different abundancebetween 10mand 30msamplingstations.
A: detritivores
B: K-herbivores
1.5
2
1.5
1
0.5
10 m
0
30 m
0m
C: predators
10 m
30 m
D: parasitoids
1.5
0.5
0m
10m
30m
E: r-herbivores
2
1.5
£
o
1
0.5
0
10m
30 m
Fig. 6.Abundance of vegetation dwelling arthropodfunctional groups along thegradientfrom E.I. (0m)tothe
crop area (10and 30m).E.I.vegetationperformance categories ofselected classification 'mow/eicov':category
I (squares)=late mowing; category 2 (triangles)— early mowing, dense vegetation; category 3 (circles)=early
mowing andsparse vegetation. Thelines between theaverages ofarthropodfunctional group numbers('"logtransformed) aredrawn to illustrate differentpatterns among thethreeE.I.categories and donot represent
estimatedpoints inbetween thesampling stations, (a)detritivores; (b)K-herbivores; (c)predators; (d)
parasitoids; (e) r-herbivores.
23
4. Discussion
4.1. Observations comparedtothehypotheses
Itwasexpected thatduration oforganicmanagement andextensive croprotation would relate
positivelytotheabundanceofprimary arthropod functional groups andthat consequently,
predator andparasitoidnumberswouldbesupported. Itwasalso expected that improved E.I
wouldpromotetheabundanceofK-herbivores andpredatorsinbothE.I. andthe adjacent
croparea.Observationsthatmayconfirm ourhypotheses includetherelatively high
detritivoreandparasitoid numbersonfarms whichhadbothalongorganic duration aswellas
anextensivecroprotation, andincreased densitiesofpredatorsinimproved (i.e.latemown)
E.I.However, severalobservations contradicted thehypothesis:dense cropsonrecently
converted farms hadthehighest densitiesofK-herbivores andpredators;several longduration
farms hadincreasednumbersofr-herbivores;K-herbivores andparasitoidswere equally
abundant inimproved E.I.and 'grassyE.I.';increased densitiesofpredators and K-herbivores
inthecropsareawere,inseveral cases,notrelated toincreased densitiesofthesegroupsin
improved E.I.
4.2. Vegetation dwellingarthropods communityinthecrop area
Observations suggesttheoccurrence offour distinctive arthropod functional group
compositions.Outliningthesecompositionsmay explaintheobserved contradictionswiththe
hypotheses and contributetoimproved hypotheses.Thefour functional group compositions
represent ashift alongthegradient oforganicduration (involving e.g. carbon flow) and
production intensity (involvinge.g. nitrogen input).Theywillbediscussed inascending order
ofintensity:a)shortdurationwith asparsecrop,b)shortdurationwith adensecrop,c)long
durationwithintensivecroprotation, andd)longdurationwithextensive croprotation.
a)Recently converted farms whichdidnothavealuxuriouscrop growth andwhichhada
poorunder story(corresponding tofarms HandZ).
Cropareaswerecharacterised byrelatively lowdensitiesoff allfunctional groups.Theselow
densities areoften encoutered infield centresofconventionally managed crophabitatsthat
includealmostnoarableweeds,particularlywhenr-herbivores arenotconsidered (Kromp&
Meindl, 1997).Establishment ofseveraltaxamayrequiretime(Hald &Reddersen, 1990).
This'unsaturated'arthropod community maydevelop,during atleast onecroprotation,
towards acommunity oftyped)orc),depending onthefarm's (rotation) intensity. However
recentlyconverted farms represent relatively unstable farming systems (oral communication
G.Oomen)inwhich stillunbalancedN-availabilityand/or apparent crop susceptibility may
rapidly changeacommunity oftypea)intoacommunity oftypeb).
b)Shortorganicduration with adensecroprepresents farms intheconversion process
(corresponding to farms BandE),involving theadaptationby soil life tochanged manure
management, andcreating asite-specific balancebetweenN-applicationandcrop
requirements.
Inthisunstable situation luxuriousgrowthmayoccurandprovide arich food resource for an
arrayofK-herbivorous taxa.Inthedensecanopywithdampmicroclimate, several
detritivorous dipterataxaareenhanced bydecaying leaves (Weberetah, 1997).ThelargeKherbivorepopulations inthesecropsrelated tohighpredator densities(Pearson correlation
betweenpredators andK-herbivores incroparea:0.81,P<0.001).But alsodetritivorous flies
mayhave supportedpredators like,for example,empidid flies. Allgroupsofherbivores,
detritivores andpredatorshadhigh speciesrichness,probablyrelated totherich food
24
resource.Highpredatordensitiesmayhave affected r-herbivores andparasitoids,whichwere
lessabundant than intypec).
c)Longduration farms withanintensivecroprotation (corresponding to farms T,L,KandJ)
may supportthedetrital subwebtoamuch lesserextentthan longduration farms withan
extensive croprotation; lowdensitiesofdetritivoreswereobserved here. Therefore
polyphagouspredatorsmaybelessabundant andtherefore have lesseffect ontheherbivore
subweb arthropods.Alsocropsmaybemoresusceptible forherbivory duetothepresenceof
moreN,andcropsneedingmoretillageinthecroprotation. Density of (polyphagous)
predators andresistant cropphysiology arecomplementary factors controlling r-herbivore
outbreaks (Embden, 1988);systemswith 'moderate'levelsofboth factors might alreadybe
vulnerable.Thelongduration farms had amorediversearthropod community ascomparedto
typed),involving acoexistence of severalpredacious taxaandK-herbivores inlowdensities.
Howeverthepredators could apparently not inhibit outbreaksofr-herbivores. The r-herbivore
outbreaksmayhavesupported theobserved highparasitoid numbers.
d)Longduration farms with anextensive croprotation (corresponding tofarms OandS)had
increasednumbersofdetritivoreswhichmayhaverelatedtoanincreaseddetrital subweb
supported bycropresidues andorganicmanure (e.g. Heimbach &Garbe, 1997;Weberet al,
1997).Polyphagous epigeicpredatorsmightbesupportedby anincreased quantity of
detritivorous prey(Wiseetal., 1999)andsubsequently depresstheherbivore subweb
includingr-andK-herbivores andoligophagouspredators.Alsolessnutritiveandless
susceptible croptissuesmay explainthelownumbersofherbivores in alongduration,with
extensivecroprotation (Phelan, 1997;Theunissen, 1994;VanEmden, 1988).Parasitoidswere
themainpredacious functional group inthecanopy,possibly duetoreduced interference by
vegetation dwellingpredators (cf.Tscharntke, 1997).Hostsofparasitoidsmighthavebeenrherbivores occurring inlowdensities andalsodetritivorous diptera (Potts&Vickermann,
1974).Parasitoid abundance onall studied farms appeared tobe significantly correlated to
detritivore abundance (Pearsoncorrelation coefficient=0.52; P<0.06) andnot tor-herbivore
abundance,whichmay expressbothdirect(e.g.food) andindirect(e.g. predatorrelease)
factors affecting this functional group.
Threeofthe studied farms corresponded only slightlytothepresented typology.FarmFwas
most similartotypea).However, lowarthropod densitiesonthis farmwereduetovery
sparsecropstandsnearthecrop edgeandcropcentre,related tomechanicalweedcontrol.
FarmMwassimilar totypec),butonthisintegrated farm estimated cropN-requirements
werepartially supplied byartificial fertilisers. FarmRwasrecentlyconverted and
corresponded therefore totyped);however, duetowetharvest conditions inthepre-crop,the
investigated crophad asparse stand including arelatively dense anddiverseweed vegetation
whichrelated toincreased arthropod abundance.
Itmustbenotedthat theextensive organic arable farms inFlevoland areprobably more
intensivethantheorganic farms studiedbyMoreby&Sotherton (1997)and Reddersen
(1997).Relatively extensive organic farms inFlevoland havecroprotations including
potatoes andvegetables,and aresituatedinintensively farmed open landscape.Thismightbe
illustratedbythetotaldensitiesofvegetation dwelling arthropods (collectedbymeansof
suction sampling);averagedensities found inorganic cereal fields inFlevoland were9-15%
oftheaveragedensitiesfound byMoreby &Sotherton (1997),Reddersen (1997)andPotts&
Vickermann(1974).
25
4.3. Vegetation dwellingarthropodcommunity intheecologicalinfrastructure
Effects ofE.I.characteristics andparticularly of'improved E.I.1willbe explainedby
discussingtheresponses ofthedifferent functional groups.
4.3.1. K-herbivores
K-herbivoreswereequally abundant inimproved (i.e.enlarged and latemown) andin
traditionally managed 'grassy'E.I.However speciesrichness anddiversity weregreaterin
improved E.I. Weevilsweretheonly differentiating K-herbivorous species for improved E.I.,
andmayhaveindicated cloversinthegrassstripsofenlarged E.I.Thearthropod community
in'grassyE.I.'waspredominated (55%ofindividuals) byherbivores:hoppers andchloropid
flies. Thiswasprobably duetotheprolonged vegetative development of frequently mown
vegetation.Accordingly, Haugthon etal.(1999)observed highernumbersof arthropods
(mainlyheteroptera) under afield marginmanagement ofcutting twice ascomparedto
cutting once.Intheirexperiment, onecutperyearwasfound tobedevastatingbecauseit
inhibited thelife cycles ofhoppersandbugs.Althoughthis effect could notbe assessed inlate
mownE.I.priortoitsmowing date,observations inthe'intermediate'management type
seemedtoconfirm theconclusion ofHaugthon etal.(1999).Thismanagement is often
appliedbyfarmers whoareconvinced thatthereisnoneed for frequent mowing,butwhoare
notabletodotheextra labour(e.g.finger-bar mowing)required for improved management.
Vegetation ofthiskind ofboundaries lost itsadaptationtofrequent mowing andbecame
colonisedbyruderaldicots,e.g. dandelion;bothplant growthandherbivore community
seemedtobemuchmoredisturbed following afirstcut after May 15thwithaflail mowerset
atalowcut levelthan following traditional management.
4.3.2. Predatorsandparasitoids
Predatorswerepromotedby'improved E.I.1withregardtobothnumbers anddiversity.
Accordingly, Wakeham-Dawson etal.(1999)found atwotimesincrease ofspidernumbers
inlonggrazedascomparedtoshortgrazedvegetation andarguedthatvegetation structureis
akeyproperty (Curry, 1994).Theobservedpredator numberswereparticularly correlatedto
detritivore numbers andnottoherbivorenumbers.Predatorswerelessabundant in'grassy
E.I.'(with abundant herbivores) ascompared toopen swards.Inopen swards,spiders,the
generallypredominant species inthepredator functional group,wereaccompanied byahigh
proportion ofants.
Highparasitoid numberswerealsorelatedtoimproved E.I.,although thesenumberswere
muchsmallerthannumbersinthecrop,suggestingthatthegroupismoreaffected bycrop
areafactors. Howevertheincreasedproportion ofparasitoids inthearthropod communityof
'grassyE.I.'maysuggest arelationtotheabundance ofhomopteranhosts.
4.3.3. Detritivoresandr-herbivores
Thesegroupswerenot included inthehypothesesbecausetheywereexpected tohave little
importance.However thedetritivorous component oftheE.I.vegetation dwellers showedto
beverysignificant, particularlyinimproved E.I.Possiblydetritivorous diptera andwoodlice
were favoured bytheincreased amount offibrous litterandstalks and ahigherhumidity in
tallvegetation. Theearliermown vegetation of'grassy E.I.'mayprovide another litterquality
that supportsother,not sampled,taxa,e.g. fungivorous staphylinids (Smeding etal, 2001a).
r-Herbivores hadvariablebut generally lowabundance inE.I.andnosignificant differences
betweenmanagement typeswere found. Numbers ofaphidsinE.I.werehighly correlated
withnumbersinthecrop(Pearson correlation coefficient=0.96, P<0.0001).However,
distinctive cropcommunities withmanyorfew aphidsweremoreor lessevenlydistributed
overthedistinctive E.I.management categories.
26
4.4. Differences and interactions between crop area and ecological infrastructure
4.4.1. Differences
According to the hypotheses predators, K-herbivores were more abundant and species rich in
the E.I. as compared to the crop area. Detritivores were more abundant and both more species
rich and diverse in the E.I. The vegetation dwelling arthropod community included several
differentiating taxa compared to the crop area. These observations clearly indicate the
increased resource of various plant tissues and structures in perennial vegetation as compared
to annual crops (Curry, 1994). Parasitoids and r-herbivores were more abundant in the crop
area. Only two taxa were significantly more abundant in the crop than in the E.I.; according to
observations of Venhorst et al. (in prep.), aphidophagous syrphid abundance increased
towards the crop centre, probably due to the increase of prey availability.
The ratio between E.I. and crop arthropod numbers (excluding aphids) on the 13 studied
farms, was on average 2.8. However, including aphids, seven of 13 studied farms had more
arthropod individuals per m in the crop area than in the E.I. Accordingly Remmelzwaal &
Voslamber (1996) found in Zuid Flevoland, the highest arthropod numbers in the E.I. in
spring and early summer, whereas numbers (of particularly crop herbivores) became higher in
the crop area later in the season.
4.4.2. Interactions
Visual assessment of E.I.-crop area gradients suggested that higher average densities in the
E.I. of predator, K-herbivore and detritivore functional groups might relate to increased
average densities in the adjacent crop area. However crop area conditions could have a much
stronger effect on the distribution of these groups. In particular, crop canopy density
supporting K-herbivores, and factors supporting detritivorous diptera, may offset potential
E.I. influence on the crop community.
Difference between the 10m and 30 m sampling station with regard to abundance, species
richness and diversity of K-herbivores, detritivores and predators were generally insignificant,
indicating that the influence of E.I. on the crop community in the summer, may stop before 10
m or might reach further than 30 m.
Aphids in the crop area may be transported and accumulated into emergent structures like
ditch slopes and tall vegetation (Hradetzky & Kromp, 1997). This might explain the
correlation of E.I. predator abundance to aphid abundance in the crop (Pearson correlation
coefficients. 69, P<0.01). Intermediate numbers of parasitoids and aphids at the 10 m
sampling station may indicate the effects on these groups of arthropods (e.g. predators) in the
field margin.
Detritivorous diptera taxa, emerged in the crop area, may also accumulate in the E.I.; however
an increased diversity and occurrence of differentiating species in the E.I. suggested that this
group is at least partly autochthonous in the field margin habitat.
4.5. Conclusions
Comparison of vegetation dwelling arthropod functional groups in the wheat crops on thirteen
organic arable farms suggested that both organic duration and 'intensity' are determining
factors. Intensity relates to crop rotation (i.e. percentage gramineous crops) but also to soil
nutrient level. Observations provided no support for the general hypothesis that organic
duration and extensive crop rotation would promote abundance of both primary arthropod
functional groups and consequently, support predator and parasitoid numbers.
27
Resultsindicated ashift orsuccession inarthropod functional group compositions from
recentlyconverted farms to longduration farms with extensive croprotation. Inrecently
converted farms pest susceptible crops,e.g. duetoluxurious growth,may attract various
herbivores andtherefore supportpredator abundance.Inlongduration farms, arthropod
communities arenotnumerousbutmorediverse.However inthesecommunities,related also
tocropcondition,particularly r-herbivores (aphids)maynotbecontrolled. However, in
extensive croprotation a'subsidised increased detrital subweb',related toincreased total
organicmatter input,may supportpolyphagous predators.Thesepredatorspossiblydepress
theherbivore subweb (i.e.herbivores andspecific predators)bybothpredationand
competition. Inthiscommunity, aswell asinotherobserved communities,effects of'predator
interference' couldplay arole,e.g. inreleasingparasitoids from predation orcompetitionby
(oligophagous) vegetation dwellingpredators.
Accordingtoourhypotheses improved E.I. (i.e.largearea and latemowing)promoted the
predacious functional groups.Howeverherbivore abundancemay alsobehigh inthe
traditionalmanagement. Thedetrital functional group (particularly diptera) contributed
stronglytothedistinctionbetweenimproved E.I.andotherE.I.typesandwastherefore a
moreimportant component intheE.I. arthropod communitythanweexpected. E.I.had
generallymuchhigherdensitiesofnon-pest arthropodsthanthecrop areaandthese
arthropodsmight therefore disperse intothecroparea.However itwasdifficult todetectthese
E.I.effects because cropconditions werevariablebetween farms andcrop areaconditionshad
astrongeffect onfunctional group abundancewhich mayhaveoffset theE.I. effect.
4.6. Recommendations
Furtherresearchrelated tothis studymayconcerntheimpact ofdetrital subsidy(Wiseetal.,
1999;Polis&Hurd, 1996)inarable farming systems,andmight specifically address
predation pressure incropswhereepigeicpredatorsfindabundant detritivorousprey.Herethe
conceptual issue isindirect control oftheherbivore subweb,includingpests,by management
ofthedetritivore subweb,i.e. the soilsystem (DeRuiter etal, 1993;Brussaard, 1998).
Connected withthethemeofdetrital subsidy,arestudiesonhighertrophic levelsinthe farm
food web,which aresupportedbyboth detrital andherbivore subwebs.Relationsbetween
bothprimary subwebsmay affect food availability for insectivorousbirdsthat havevalue for
nature conservation.
Interference betweenpredatorsmightbeanother important research topic.Information on
intraguildpredation andsubsequent releases oftaxa at lowertrophiclevels,might explain
features that arepossibly commoninarthropod communities onfarms (Tscharntke, 1997).
Appropriate studyareas forresearchwithregardtodetrital subsidy,predator interference and
food webstructure shouldinclude,preferably, acombination ofrelatively similar
(commercial) farms, and additionally experimental fields for testing extreme management
options.Practice farms areimportant studyobjects,because effects mayonlyoccur ina
farming system,and suchfarm level experiments arevery expensive;anotherreason isthat
experimental manipulation onfarms mustnecessarily remainwithintheboundaries oforganic
agriculturalproduction systemswhichmay safeguard the later applicability ofresearch
outcomes.
Withregardto functional group assessment, improved definition oftheassemblages is
needed. Inparticular,herbivorous taxamightbe aggregated inamore sophisticated way.For
28
exampleHald&Redderson (1990) distinguished crop-related andnon crop-related
herbivores,and Tscharntke (1997)distinguished endo-andectophagous species.
Foroptimisation ofE.I.withregardtoarthropod functional groups,further comparative
research including experiments ofmowingregimesmightberequired (e.g. Boatmanet ai,
1999;Remmelzwaal &Voslamber, 1996).These studies should alsotakeinto account
detritivorous androotherbivorous arthropods.Additional attention inarablefieldmarginsis
required for abundant molluscsandearthworms andtheeffects ofantnestsonthe arthropod
community.
Withregard topractice,results suggestthat improvingthe ecological infrastructure is
worthwhile: inparticular, latemowing isimportant toenhance arthropod numbersand
diversity.However, frequently mownmarginswithintact swardscanalsoharbourhigh insect
densities.Itmightbebettertoavoid an'intermediate'typeofmowingmanagement, involving
few cutsperyearand alate(June) first cuttogroundlevelwithaflail mower. This
management isprobably deleterious for arthropod abundance.Withregard tothepromotion
ofbeneficials inthecrops,moreresearchisstillneededtofind soundlybasedpractical
recommendations relatingtocropandecological infrastructure management.
Acknowledgements
Theauthorswould liketothankthe farmers whoallowedusaccesstotheir land,andKees
Booij andClasienLock(PRI-WUR)whogavevaluable suggestions andprovidednecessary
equipments.TheworkattheWageningen University isfunded bytheMinistry ofAgriculture,
NatureManagement andFisheries,Department of Science andKnowledge Dissemination.
29
Chapter 3: Shifts infunctional group composition ofground
dwelling arthropods inrelation toecologicalinfrastructure and
conversion toorganic farming
F.W. Smedinga,C.A.M. Lockb&C.J.H. Booijb
"DepartmentofPlant Sciences, Biological Farming Systemsgroup, Wageningen University, Wageningen,
TheNetherlands
''PlantResearch International, Wageningen, TheNetherlands
Abstract
Hypotheses on therelation of farm management and ecological infrastructure (E.I.) characteristics to the
functional group composition ofground dwelling arthropods inthe crop and E.I.were tested on organic arable
farms. The study area included 8farms that varied with regard tothe studied traits.Arthropods were collected by
pitfall traps inwheat crops and adjacent canalbanks. Observations in the crop area suggested that the arthropods
were affected by farm 'intensity', as defined by crop rotation, manuring and soil cultivation. Broadly in
accordance with thehypotheses, relativelyhigh abundance ofpredacious beetles, lycosid spiders, granivorous
beetles and folivores were found incrop areaswith acomparatively low 'intensity'. In contrast tothe hypotheses,
small staphylinid beetles, asrepresenting thedetritivores, seemed tobe associated with ahigh 'intensity', andthe
linyphiidspiders suggested anassociation tolarge continuous fields. Contrarytoimproved E.I., traditionally
managed E.I. enhanced specific groups like lycosid spiders, small staphylinids as well as ground dwelling
herbivores. Improved E.I.did not support ahigh density ofground dwellers in the summer. Comparison of crop
area and E.I. observations suggested that themost numerous epigeic groups (predacious beetles and linyphiid
spiders) inboth crop area and E.I.were affected by crop area conditions. Possible interactions between epigeic
arthropod predators arediscussed with reference to field observations.
1.Introduction
1.1.Biodiversity-loss in agriculture
Populations ofvarious animal andplant specieson farmlands inindustrialised countries are
seriouslydeclining duetoagricultural intensification (e.g.Paoletti, 1999;Fulleretal.,1995;
Andreasen etal, 1996).Thisbiodiversity-loss isamatterofgreat concern for ecologists,
agriculturists aswell asthe generalpublic(Paoletti, 1999;Wood &Lenne, 1999),whoare
increasingly awareofboththeintrinsic aswell astheeconomicvalueofbiodiversity.
Toreversethistrendofbiodiversity-loss, development ofmulti-species orsustainable farming
systemsisprobablyneeded (Vandermeer etal, 1998;Altieri, 1994, 1999;Almekinderset al,
1995).These farming systemsutiliseecosystem servicesprovidedbybiodiversity (e.g.pest
control, soil fertility) andmay alsogiveroom fornatureconservation-worthy biodiversity of
whichtheutilityisnotclear(Duellietal.,1999).Severalexamplesofmulti-species farming
systempractices areelaborated byAltieri (1994),Wood &Lenne (1999),andotherauthors.
Development ofmulti-species farming-systems mayrequire specific research approaches,
particularly withregardtothestudy areaandstudiedvariables.Firsttheresearch shouldtake
site-specificity ofbiodiversity into account (Vandermeer etal, 1998),and should preferably
start from 'nearlynatural systems'which exhibit theprocesses onwhich ecosystem services
arebased (Brown, 1999a).Secondthevariables,should specifically addressthe farm-, or
higher levelsofaggregation (Almekinders etal, 1995),andtherefore addressthewhole
biocoenosis (Biichsetal, 1997).Thismayinvolverecognition oftheholistic conceptthatnot
31
all structures atthesystem levelcouldbepredictedbycomponent knowledge(Stobbelaar&
VanMansvelt, 2000;Bockemuhl, 1986;Sheldrake, 1988, 1991).Third thepredictor variables
shouldremainclearlyrelated todecisions inthefarm management, sooutcomes canbe
translated tofarming practice andpolicy,includingmanagement ofsemi-natural habitatson
thefarm (Vereijken, 1998;Smeding&Joenje, 1999;Park &Cousins, 1995).
1.2.Organicfarms andecological infrastructure
Among appropriate objects inEurope for empirical system-oriented research on farm
biodiversity areprobably organic farms, corresponding toproduction guidelines 2092/91in
theECcountries (Anonymous, 1991);themaintenance andutilisation ofbiodiversity is
inherent tothephilosophy oforganicfarming. Researchprovidesevidence that organic
farming ascompared toconventional farming involvesincreased numbers and species
diversityofbirds(Chamberlain etah, 1999;Braaeetat, 1988),vegetation dwelling
arthropods(e.g. Moreby &Sotherton, 1997;Hald&Reddersen, 1990),epigeic arthropods
(reviewedbyKromp, 1999),earthworms (Pfiffner &Mader, 1997),arableweeds(e.g. Van
Elsen,2000;Smeding, 1993)andhabitats(e.g. Stobbelaar&VanMansvelt,2000;
Chamberlain etal, 1999).
Ofparticular interest,because oftheirincreased similarity to'nearlynatural systems'(Brown,
1999a),mightbe farms that combineorganic croppingwith apurposefully enlarged, spatially
distributed anddiversified ecological infrastructure. Inthisarticle ecological infrastructure
(E.I.)isdefined asthetotalofsemi-natural(aquatic,woody,tallherb and grassy)habitatson
the farm including itsspatial arrangement (Smeding &Booij, 1999).Invarious farming
systems,enlarged anddiversified E.I.enhancesthenumbersanddiversity of indigenous
plants andanimals atthe farm level,includingthecroparea(e.g. Joenje etal.,1997;LaSalle,
1999;Boatman etal., 1999).Inorganic farms thismaycontribute topest control (Kromp&
Meindl, 1997;Theunissen &Kohl, 1999)andtosoil fertility (Brown, 1999b).
1.3. Foodweb approach
Anappropriate methodology forbiodiversity research, addressing variables athigher levelsof
aggregation,isoffered byrecentadvancesinresearchoffood webs(Polis&Winemiller,
1996;Pimm, 1991).Theseadvances,including some studiesinagricultural habitats (e.g. De
Ruiteretal, 1995;Tscharntke, 1997),areproviding inspiring examplesofhow (agro)
ecosystems canbeapproached athigher integration levelsthanthe species-level. Someofthis
researchindicatesthat farm food webs canmediatetheeffects ofenvironmental factors on
species(Wiseetal, 1999;Tscharntke, 1997).
Ourgeneralhypothesis aboutthefarm food webonorganic arablefarms with improved E.I.
isbased onthree sub-hypotheses:
Firstthatthedetrital webisenhanced bytheincreased organicmatter input,involving organic
manure,compost andcropresidues (ofcerealsand leypasture),andrelates to increased
numbersofinvertebratemeso-andmacrofauna (e.g. Pfiffner &Mader, 1997;Weberet al,
1997;Idingeretal, 1996;Heimbach &Garbe, 1996). Second that numbers ofvariousnonpestherbivorous functional groups areenhanced byimproved E.I. (Holland &Fahrig,2000;
Boatman etal, 1999)but alsobyorganic cropcharacteristics (Hald &Redderson, 1990;
Morbeby &Sotherton, 1997).Third,combined increaseofdetrital andherbivore invertebrates
relates toacumulative positive effect ontheabundance ofpredatorswhich feed onprey from
bothdetrital andherbivore subsystems (Wiseetal, 1999;Idingeretal, 1996;Sunderlandet
32
al, 1996a;Kromp, 1999).Thiseffect isacceleratedbythe frequently occurring food shortage
onfarms, limiting theabundanceofbothpredacious invertebrates (Booij etal., 1996)aswell
asvertebrates (Poulsen etal, 1998).
Additionally weexpectthat successionof food webstructurerequirestime(Idinger &Kromp,
1997;Idinger etal, 1996),possibly uptoatleastoneortwocroprotations.Former
application ofpesticides anddepletion oforganicmatter andsoilcompaction duetoreliance
onartificial fertilizers maynegatively influence therateofthissuccession{e.g. Paoletti,
1999).
1.4. Hypothesesandobjectives
Ourfieldstudywasfocussed onfunctional groupcomposition ofground dwellingarthropods,
comprising detritivore,herbivore andpredator groups.Particularly theepigeicpredatorshave
major quantitativeandfunctional importanceinthefarm foodweb,linkingthedetritaland
grazerfood chains (e.g. Kromp, 1999;Sunderland, 1991).Complementary studies,published
elsewhere,weredevotedtovegetationdwellingarthropods (Smedingetal.,2001b)and
insectivorousbirds(Smeding &Booij,2001).
Applyingthe farm food webhypotheses toground dwelling arthropod functional groupswe
expectedtofind moreepigeicpredators,detritivores andherbivoresincropsoforganic farms
withalongduration and/or extensive croprotation (i.e.highproportion ofgramineouscrops).
Wealsoexpectedtoobservepositive effects ofimprovedE.I. (i.e.largeareaand appropriate
management) onthe abundance ofpredacious andherbivorous functional groups inboth
cropsandE.I.Althoughpartsofthishypothesesarealreadytested (references mentioned
aboveande.g. Ryszkowski etal.(1993) andRyszkowski &Karg (1991),whocompared
above-ground insectbiomassinvariousagriculturallandscapes),hypothesesintegratingthe
effects ofduration oforganicmanagement andeffects ofE.I.management on functional
groupcompositionhavenotbeentestedso far.
Thus,theobjectives ofthisstudywere:
1. todeterminetheabundanceofground dwelling arthropod functional groupsinthecrop
areaandintheecological infrastructure oforganicfarms, andrelatetheabundanceof
these groupstocrop areaand ecological infrastructure characteristics;
2. torelatethe abundance ofground dwelling arthropod functional groups inthecropareato
their abundance inthe ecological infrastructure.
2. Materials and methods
2.1. Studyarea
Thestudywasdoneonorganic farms intheprovince ofFlevoland,TheNetherlands.The
farms arelocated inthethreepoldersNoordoostpolder, Oostelijk Flevoland andZuidelijk
Flevoland (Fig.l). Thesethreepolderswerereclaimed around 1940, 1957and 1968
respectively, and aredominated byagricultural landuse.Thesoil isacalcareous clay-sandy
clayofmarineorigin.Flevoland waschosenasastudy areabecause ithasaconcentration of
organic farms that aresimilarwithrespecttotheirhistory andtopography. Therearecurrently
75economically viableorganic arable farms inFlevoland, which aregenerally large(c.30-70
ha)andintensiverelativetootherorganic arable farms inEurope.
33
Eight farms wereselectedbasedondifferences incrop areaandE.I. characteristics (Table 1).
Theselection included sevencommercial organic farms andone experimental farm. The
selected commercial farms wereall arable,althoughtwo(farms NandT)possessed astable
with livestock, whichreceived fodder crops from thesamefarm but grazed elsewhereduring
thesummer. Theexperimental farm ofWageningenUniversity (farm E)isamixed dairyand
arable farm. Fourcommercial farms (farms A,T,L, andD)wereEcological Arable Farming
Systems(EAFS)prototype farms during 1992-1997(Vereijken, 1997);amongthese farms,
farm Aisdifferent becauseitissituated intheyoungest polderZuidelijk Flevoland andjoined
theEAFS-project afew yearslaterthantheothers.FarmsAandNstarted in 1985onan
experimental reclamation area,which hadnever received pesticides.
w
Fig. 1.Study area. Theinvestigated organic arablefarms are represented by closed circles.
2.1.1. Croparea characteristics
Organicduration oftheselected farms ranged from onetotwelveyears.Ploughingisdone
generally at25-30cmdepth. Onallthe farms a6-7 yearcroprotation ismaintained,with
6-11different cropsper farm. Together thefarms comprised 542ha arableland withper farm
15-33%cereals,0-36%leypasture, 10-31%traditional lifted crops(potatoes, sugarbeet)and
19-69%vegetable crops.Vegetables involvemainly onions,runnerbeans,variouscabbages,
peas,andsweetcorn.Thefarms withmostextensivecroprotationshadahighpercentage
(>30%)ofgramineous crops(cerealsandleypasture) andtherefore alowpercentage (<50%)
ofvegetablecrops.Ascomparedtoothercrops,gramineous cropsprovide alargeamountof
carbon incropresidues andrequire few soildisturbing operations.Because inputofnutrients
(N,P,K)hastobe adjusted tocroprequirements, andvegetables need morenutrients than
cereals,intensity ofcroprotation isassumedtorelatetoboththeamount ofcropresiduesand
the amount ofN-applicationatthe farm level.
34
Table1
Characteristics of thefarms and ecological infrastructure and totalnumbersperform of arthropod functional
groups captured inweekly trappings over aneight weekperiod inthe wheat crop (30mfrom the field margin)
and in theecological infrastructure.
Level
Farm
Farm
Farm
Farm
E.I.
E.I.
E.I.
E.I.
E.I.
E.I.
Variables
n Yearoforganicfarming (n)
Cerealsandleypasture (%)
Cropswithin 100mrangeofE.I. (%)
Semi-natural habitat (E.I.) (%)
Mowingdate(farm level)(month)
Mowingfrequency (n/year)
Heightvegetation (m)
Covervegetation (%)
Speciesdiversity vegetation (n/4m2)
Dominant speciesdiversity (n/4m2)
Agepolder (year)
Crop
Crop
Crop
Crop
Crop
Crop
E.I.
E.I.
E.I.
E.I.
E.I.
E.I.
D
8
35
72
3.5
7
2
1.4
95
16.0
3.8
57
L
E
10
4
11
61
80
90
3.1
4.5
6
6
2
2
0.8
1.5
100
85
13.2 11.8
3.0
3.4
41
41
A
12
38
47
2.1
7
2
0.4
98
10.5
3.4
30
N
12
59
40
0.8
5
3
0.5
67
9.3
2.8
30
Predaciousbeetles
Lycosid spiders
Linyphiid spiders
Small staphylinid beetles
Granivorous carabids
Folivores
1731 1333 3765 1011 1035 2889
8
57
38
18
83
35
1944 2979 2622 2515 2055 1687
541 893 425 640 772 205
15
7
4
3
19 504
5
7
21
13
6
8
952
53
3061
1308
5
4
1064
146
3311
329
83
3
Predaciousbeetles
Lycosid spiders
Linyphiid spiders
Small staphylinid beetles
Granivorous carabids
Folivores
926
64
2554
709
66
100
1365
87
2508
739
52
104
1319
535
2577
703
149
275
dur
int
ei 100
area
mow
mowfrq
eihgt
eicov
eispn
eidom
lsage
T
8
38
74
2.3
9
1
2.4
95
12.0
3.4
41
F
7
24
74
1.4
5
2
1.1
88
9.5
3.1
41
1205 2808
208 302
880 4235
444 334
83
79
150
33
R
1
18
65
1.6
5
3
0.7
77
7.5
2.3
41
832
46
1191
365
253
38
1706 2603
168 226
1607 1930
217 411
291 279
61
35
2.1.2.Ecologicalinfrastructure characteristics
TheEcological Infrastructure (E.I.)of arable farms inFlevoland ismainlydeterminedby
canals andbanks(together c.3-4mwidth)that arelaidoutaslinearherbaceous boundaries
adjacent tothecrops.Onfivefarms, boundaries arewiderbecause of adjacent (2-3mwide)
grassstrips,often includingclovers(Trifolium spp.),ononeorbothsidesofthecanals.Farm
Ealsohasgrassstripsbetween cropplots.Percentages ofE.I.higherthanc.2%(Table 1)
weremainly duetothepresence ofthesegrass strips.Onlyfarms Land Epossessed a
boundaryplanted with ahedgerow. Spatialdensity ofE.I.ispurposefully increased on farm E
(Smeding &Joenje, 1999)and farm L.Thespatial arrangement ofE.I.ontheother6 farms
mainlyreflect landscape scale.
Extremetypesofvegetation management are:
- 'traditionalmanagement' involvingthreeor four morecutsperyearwithaflail mower
leavingthe shredded cuttings in situ;
- 'latemowingmanagement' involvingoneortwocutsperyear after June21 stwitha fingerbarmowerwith ahiabgrab forremoval ofcuttings.
Thegrassstripsalongthecanals arerequired forfieldtransport in'latemowingmanagement'.
TheE.I.areais,therefore, related tothemowing date.Inthis articletheE.I.withenlarged
areaandlatemowing isdefined as'improved E.I.'.Theimproved E.I.onthe four farms (A,T,
L,andD)wascreated duringtheEAFS-prototyping researchprogram in 1992-1997
35
(Vereijken, 1997, 1998).Theimproved E.I.ontheexperimental farm Estarted in 1995
simultaneously with conversion oftheconventional dairy farm toanorganicmixed farm
(Smeding&Joenje, 1999).
Dominant plant species incanalbank swardsare:couch (Elymus repens),perennial meadow
grasses (Festuca rubra,Poatrivialis,Loliumperenne,Agrostisstolonifera),commonreed
(Phragmitis australis)and afew perennial herbs:dandelion {Taraxacum officinale) and
stingingnettle (Urtica dioica).Canalswithtraditional managementhavealow,relatively
open, speciespoor vegetation (<10species/4m2),dominatedbyafew grass species.Late
mowingparticularlyrelatestoincreased vegetationbiomassinJuneandJulyasexpressedby
vegetation height (upto 1-3 m)and cover(upto90-100%).However, latemowingdoesnot
necessarily relatetoincreased higherplant speciesdiversity for tworeasons:a)tall grass
speciesmaydominate thesward;b)swardsoftraditional management may locallybecutto
ground levelandtherefore beinvadedbyruderals and annuals (increased speciesnumberup
to 15species/4m2),e.g. thistles (Cirsium arvense, Sonchusarvensis),annualweeds(e.g.
Sonchusasper,Polygonumaviculare)and annualsthatarerarelypernicious weedsin
Flevoland (e.g. Myosotisarvensis, Veronicapersica, Cardamine hirsuta).
Highperennial plant diversities found insome locationsmayrelatetovarious interrelated
factors (Kleijn, 1997):reduced vegetation productivity,removal ofhay,nutrient buffering by
thegrass strip,andlongorganicduration.However, also,artificial speciesintroduction is
involved; intheEAFS-project, around 90different nativeperennial dicotswere artificially
seededinthecanalbankstoobtainhigherplant diversityand flower abundanceofplantswith
limiteddispersal capacity (Vereijken, 1998).Although few specieswere ableto settlewell
(e.g. Seneciojacobea, Crepis biennis, Heracleum sphondylium), theintroduction clearly
affected speciesdiversity:vegetation includingsiteswith>15species/4m wereconfined to
prototype farms.
2.2.Samplingandmeasurements
2.2.1.Arthropodsampling
Samplingwasdoneinwheat cropsandinadjacent canalsbanks (E.I.)which were situatedin
theinterioroftheorganic farm area.Wheat (Triticum aestivumL.)waschosen asa
representative crop asthiscropiscommon onorganic arable farms inFlevoland and
arthropod numbers incereals arelargecompared tonumbers inothercommon cropslike
potatoesandonions(Booij &Noorlander, 1992).Withinonewheatfieldoneachoftheeight
farms one60x30m2 sampling areawasselected; thisareawas 60m longbordering acanalby
30mperpendicular tothat canal.Sixpitfall traps (10cmdiameter) wereplaced inarowwith
intervalsof 10matdistancesof0m(E.I.) and30m(wheat) from the field boundary. Traps
contained apreservativeof4% formaline plusdetergent. Weekly samplesweretaken during8
weeks,startingfrom 6thofJuneuntil28th ofJuly 1998.Theobservations ofthesixtrapsand
eight sampling datesweretreated separately, giving 48measurementsperhabitat (cropor
E.I.)per farm. Springtails (Collembola), andants(Formicidae)werediscarded because pitfall
trapsdonotgiverepresentative measurements ofthesegroups.Arthropodswere storedin
95%alcohol.Individuals weresortedtotaxaatorder- orfamily-level andplaced intosix
different arthropod functional groups:
- Predaciouspolyphagousbeetles including carnivorous Carabidae and large (>6mm)
staphylinid beetles;
- Lycosid spiderswhich arerelatively largepolyphagous predators andrepresent diurnal
wandering spiders (Marcetal, 1999;Sunderland, 1991);
36
- Linyphiid spiderswhich arerelatively small species andrepresent highly dispersive sheetweb spiders (Marc etai, 1999;Sunderland, 1991);
- Small staphylinid beetles oftheepigeobiontic lifeform (Bohac, 1999)which aremainly
fungivorous andrepresent thedetritivore functional group amongepigeic arthropods;
- Granivorous carabidbeetles (generaAmaraandHarpalus)representing the invertebrate
granivore functional group;althoughthese carabidsmay feed, tosome extent,on
invertebrates aswell(Westerman etal, inprep.);
- Folivorous herbivoresrepresentedbyweevils(Curculionidae) and leafhoppers
(Cicadellidae).
2.2.2. Vegetation measurements
Vegetation studiesincluded theE.I.wherepitfalls werelocated. Theinvestigation wasdone
from MaytoAugust:latemownvegetationwassampled inJune-Julybefore thefirstcut.
Early andor frequently mown vegetation wassampledbefore thefirstcut (May)orlater (until
August)when species composition couldbeidentified adequately. Theherb layerwas
sampled insevenplotsof4m2areawith intervalsof50mbetween samples.Plotsincluded
theditchbankvegetation from thetoptothehelophytic zone;vegetation affected by flooding
wasexcluded. Parameters were:cover,maximum height,plant species anddominantplant
species (totalling 80%cover).Averageswerecalculated for each farm.
2.2.3.Farmmanagementandlayout
A 1:5000mapwasmadeofeach farm, depicting thedifferent crops andthe ecological
infrastructure (E.I.).Onthesemapstheareaofsemi-natural andcrophabitatswere measured.
The'E.I.-area' iscalculated asthepercentage ofsemi-naturalhabitat ofthefarm area (without
the farm yard).Farmrotation intensityisdefined astheproportion ofgramineous crops
(cereals andleypasture) ofthetotalcroparea.Thespatial arrangement oftheE.I.or'E.I.
density',was expressed asthepercentage ofthe farm within a 100mdistance oftheE.I.In
casethecanalbankvegetation wascutboth after September 15th andbefore May 15th,a
distance of70mwas considered. Theinfluence offieldmargins ontheabundance oflarge
carabidbeetles andspidersprobably doesnot exceed 70-100m(Booij,unpublisheddata).
Dataontheyearofconversion ofallofthe farm toorganic,husbandrypracticesinthewheat
crop in 1998,andmowing ofcanalsbanks andgrassstripswereobtained usinga
questionnaire. Themowingmanagement isrepresented bythemonth ofthefirst cut,because
thiscut largely determines thephenological stageofthevegetation inJune andJuly.
2.3.Statisticalanalyses
Data from all samplingperiodswerecombined, tested for normality and log-transformed.
Allsubsequent analyseswereconducted using Statistical Analysis System (SAS Institute,
Cary,NorthCarolina).
Individual farms wereclassified intooneofthreegroups onthebasisofcorresponding farm
andE.I.characteristics (Table 1).Withregardtothecropareasamples,the classifications
werebasedonrelevant farm level characteristics (duration,rotation intensity, areaofE.I.,and
E.I.density).Withregard totheE.I. samples,theclassifications werebased onboth farm
level characteristics aswell asE.I.-vegetation characteristics (duration, E.I.-area, monthof
first mowing,vegetation cover,vegetationheight, plant speciesnumber ordominantplant
speciesnumberper4m2).Theclassifications weredetermined bytwosplits:thefirstsplit
basedononeoftheabovementionedcharacteristics,separated acategoryof2-3farms and
thesecond splitbased onanother ofthesecharacteristics,divided theremaining 5-6 farms ina
37
second andathirdcategory. Theminimumcategory sizewas2farms.Forall obtained
classifications canonical discriminant analyseswereperformed onthenumbersofthe
arthropod functional groups.Dataofthecrop areaandoftheE.I.wereanalysed separately for
cropareaandE.I.classifications respectively. Theclassifications withthehighest Wilks'
LambdaF-valuewere selected.
Stepwise andcanonical discriminant analyseswereperformed onthenumbersof arthropod
functional groupstodeterminethemostimportant groupsthat couldclassify the farms into
threecategories.Arthropod observations inthewheat andintheE.I.were again analysed
separately. Stepwisediscriminant analysiswasalsousedtoidentify variables that contributed
mosttotheselected classification. Canonical discriminant analysiswasusedtodeterminethe
magnitude anddirection oftheassociation ofindividual variableswith indicatorvariables.
Standardised canonical coefficients largerthan 0.3dividedbythe squarerootofthe
eigenvalueofthecanonical function (Afifi &Clark, 1984)were considered large enoughto
contribute significantly tothe classification.
Differences intheabundance ofarthropod functional groupsbetween thethree categories
weretestedbylinearregression (GLM)using
the 10log-transformed measurements and
u
including aDuncan'smultiplerangetest.
Thecombined data-set ofwheat andE.I. sampleswasusedtoanalysetheabundanceof
arthropod functional groups alongthegradientfromE.I.tocropcentre,representedbytwo
sampling distances0m(E.I.)and 30m(wheat)fromthefieldmargin. ANOVAwas
performed onthetwoselected classifications todetermineinteractionsbetween distanceand
category.
3. Results
3.1. Observednumbers ofepigeic arthropodfunctionalgroups
During eightweeks 77,784organisms werecaught in96pitfall traps including 40,233
organisms inthecropareaand37,551organisms intheEcological Infrastructure. Croparea
samplescomprised 33%predacious carabidbeetles, 1%large (>6mm)predacious staphylinid
beetles, 1%lycosid spiders,50%linyphiid spiders, 13%small (<6mm) detritivorous
staphylinidbeetles,0%folivores and2%granivorous carabidbeetles.E.I. samples comprised
33%predacious carabidbeetles, 1%largepredacious staphylinid beetles,4%lycosid spiders,
10%smalldetritivorous staphylinidbeetles,47%linyphiid spiders,2% folivores
(Curculionide andCicadellidae) and2%granivorous carabidbeetles.
3.2. Arthropodfunctional groupsinthecroparea,affectingdistinctions amongfarm
categories
Theclassification 'int/area'based oncroprotation intensity(first split) and areaofthe
ecological infrastructure (second split)gavethebest separation ofcrop area arthropod
observations (canonical discriminant analysis,Wilks'Lambda,F-value=30.1,PO.0001;
Table2).Thesecondbest classification 'eilOO/dur'(Wilks'Lambda,F-value=28.1,PO.0001)
wasinterestingbecausethedistinction wasaffected bythethemost abundant group
predaciousbeetles,whereasthedistinction ofthebest classification wasonly affected byless
abundant groups.Therefore both classifications arepresented below.
38
Table2
Examples of classifications of thecrop area and theecological infrastructure, including the the Wilks'Lambda
F-value and thesquared canonical correlation obtained bycanonical discriminant analysis. Theabbreviations
of category characteristics areexplained in Table1.
Crop area:
Category
Farms
Category
Farms
Category
Farms
Category
Farms
Category
Farms
Category 1
int>40
NE
eil00<70
ANR
int<20
RL
int<30
ARL
dur<6
RE
Ecologica 1
infrastru :ture:
Category 1
Category eispn>12
Farms
TLD
Category eispn>12
Farms
TLD
Category eihgt<0.5
Farms
AN
Category mow>7
Farms
TED
Category eicov<80
Farms
NR
Category2
int<40 & area >2.2
TLD
eil00>70 & dur<8
FE
int>20 & eil00<50
AN
int>30 & area<2.2
FN
dur>6 & area<2.2
ANF
Category 3
int<40 & area <2.2
AFR
eil00>70&dur>8
TLD
int>20 & eil00<50
TFED
int>30 & area>2.2
TED
dur>6 & area>2.2
TLD
F-value Sq. Can.
0.52
30.1
Category 2
eispn<12 & eicov>80
AFE
eispn<12 & eihgt>l
FE
eihgt>0.5 & mow<7
FRL
mow<7 & eidom>3
FL
eicov>80 & mow<7
AFL
Category 3
eispn<12 & eicov<80
NR
eispn<12 &eihgt<1
ANR
eihgt>0.5 &mow>7
TED
mow<7 & eidom<3
ANR
eicov>80 &mow>7
TED
F-value Sq. Can.
0.32
15.9
28.5
0.46
22.8
0.34
19.7
0.32
12.0
0.19
15.7
0.33
14.2
0.27
12.7
0.25
11.9
0.23
Table3
Arthropod variables that contributed significantly toclassification of thecrop area observations in'int/area'
farm categories bystepwise and canonical discriminant analyses,standardised canonical coefficients, andmean
valuesper crop area category. Comparison ofarthropod numbers in thecategories byDuncan's multiple range
test.
Variablesa
Granivorous carabids
Lycosid spiders
Small staphylinids
Linyphiid spiders
Folivorous insects
Predacious beetles
Canlb
Mean values andmultiple rang
Standardised
coefficient
Category 1:
int>40
0.89 c
0.43
-0.39
0.15
-0.05
-0.04
mean
6.1
1.9
5.6
52.1
0.1
41.3
a
a
b
b
b
a
Category 2:
int<40&
area>2.2
mean
0.3
b
1.0
b
15.3
a
48.5
b
0.1
b
28.5
b
e comparison
Category
int<40&
area<2.2
mean
0.1
0.8
16.5
56.9
0.3
39.8
3:
b
b
a
a
a
b
(PO.0001)
(P<0.0001)
(P<0.0001)
(PO.01)
(P<0.05)
(P<0.05)
"Variables are listed in order ofselection by stepwise discriminant analysis. Italicised variable wasnot selected
by stepwise discriminant analysis.
b
Canonical function 1;responsible for 95%ofthe variation.
c
Standardised coefficients >0.29 were considered large enough for interpretation.
39
3.2.1. Classification'int/area'
Category 1 included farms with anextensive croprotation (>40%cerealsand leypasture);
category2included farms with anintensivecroprotation andalargeE.I. area(whichwere
thethree former prototype farms inOostelijk Flevoland);category 3included farms withan
intensivecroprotation and asmallE.I.area.
All arthropod functional groups exceptpredaciousbeetles,wereselected asimportant factors
by stepwisediscriminant analysis for discrimination amongthethreecategories (Table3).
Thefirst canonical function containinggranivorous carabidbeetles,lycosid spiders,and small
staphylinid beetles separated category 1 (extensivecroprotation) farms from bothother
categorieswith intensivecroprotation (Fig.2);granivorous carabids and lycosid spiderswere
positively associated, andsmallstaphylinid beetleswerenegatively associated withthis first
axis(Table 3).Inthesecondcanonical function noneofthearthropod groupshad sufficient
canonical loading;however, linyphiid spiders contributed mosttotheseparation ofcategories
2and3,andwerepositively associated withthesmallE.I. areaofcategory3.
A
D
- cJ&Acg
nDQn
°
•
1
-2
4
can 1
Fig. 2.Plot ofthesecond andfirst canonicalfunctions discriminating amongfarm categories of the
classification 'int/area'.Squares representfarms with >40%gramineous crops; circles representfarms with
<40%gramineous crops and >2.2%E.I. area; triangles representfarms with >40%gramineous cropsand
<2.2%E.I.
Onfarms withextensive croprotation (category 1),granivorous carabid beetleswere>20
timesmoreabundant onaverage, lycosid spiderswere>90%more abundant onaverageand
small staphylinid beetleswere >60%lessabundant onaverage,than ontheothertwo
categories.Linyphiid spiderswere 15%more abundant onaverageincategory 3(intensive
croprotationwith smallE.I.)thanincategory 2(intensive croprotation with large E.I.)
(Table3).
3.2.2.Classification 'eilOO/dur'
Category 1 included farms with large scaleE.I./landscape;category 2included farms witha
spatiallydenseE.I.andmoderately long(4-7years)organicduration;category 3farms hada
spatially denseE.I.and alongorganic duration (8-10years) (thesewerethethree former
prototype farms inOostelijk Flevoland).
40
10
Theseparation into'eilOO/dur'categories,based onarthropod functional groupnumbersin
wheat,isillustrated inaplotofcanonical variabletwoversus canonical variable one(Fig.2).
Allarthropod functional groupswereselected asimportant factors bystepwise discriminant
analysis fordiscrimination amongthethreecategories (Table4).Thefirst canonical function
containingpredacious beetles,small staphylinid beetles andgranivorous carabids separated
the farms with denseE.I.andmoderate duration (category 2) from bothothercategories (Fig.
2).Predaciousbeetlesandgranivorous carabidswerepositively associated and small
staphylinidbeetleswerenegatively associated withthefirstaxis(Table4).Inthesecond
canonical function noneofthe arthropod groupshad sufficient canonical loading;however,
linyphiid spiders contributed mostthe separation ofcategory 3and 1,andwerepositively
associated with alargescalelandscape (category 1).
Inextensive farms (category 1),predacious beetleswere>2timesmore abundant onaverage,
granivorousbeetles>8timesmore abundant andsmall staphylinid beetleswere>2timesless
abundant onaverage,than intheothertwocategories.Linyphiid spiderswere>20%more
abundant onaverageincategory3(largescalelandscape farms) thaninbothother categories
(Table4).
Table4
Arthropod variables that contributed significantly toclassification of thecrop area observations in 'eilOO/dur'
farm categories bystepwise and canonical discriminant analyses, standardised canonical coefficients, andmean
valuesper crop area category. Comparison ofarthropod numbers inthe categories byDuncan's multiple range
test.
Canlb
Mean values andmultiple range comparison
Standardised Category 1:
coefficient
eil00<70
Variablesa
Predacious beetles
Small staphylinid beetles
Lycosid spiders
Granivorous carabid beetles
Linyphiid spiders
Folivorous insects
0.86 c
-0.42
-0.26
0.28
-0.06
0.16
mean
21.1
15.8
1.5
0.6
61.7
0.1
c
a
a
b
a
b
Category 2:
eiI00>70&
dur<8
mean
69.3
a
6.6
b
0.8
b
5.3
a
44.9
b
0.3
a
Category 3:
eiI00>70&
dur>8
mean
28.5
b
15.3
a
1.0
b
0.3
b
48.5
b
0.1
b
(PO.0001)
(PO.0001)
(P<0.0001)
(P<0.0001)
(P<0.0001)
(PO.05)
a
Variables are listed in order of selection by stepwise discriminant analysis.
Canonical function 1;responsible for 86%ofthe variation.
c
Standardised coefficients >0.32 were considered large enough for interpretation.
b
3.3. Arthropodfunctional groupsintheEcologicalInfrastructureaffectingdistinctions among
E.I. categories
Theclassification 'eispn/eicov',basedonE.I.-species number (first split) and E.I.-vegetation
coverassecond split gavethebest separation ofobservations (canonical discriminant
analysis,Wilks'Lambda,F-value=15.9 (P<0.0001);Table2).Classifications basedonorganic
duration, E.I.area,dateoffirstmowing,E.I.-vegetation height anddominant speciesnumber
showed lessdistinction thantheclassification 'eispn/eicov'(Table2).Category 1 included
speciesrichE.I.onprototype farms inOost Flevoland; category 2included aless speciesrich
E.I.with adensevegetation;category 3included aspeciespoorE.I.with open vegetation
relatedtotraditionalmowing management.
41
Theseparation into'eispn/eicov'categories,based onarthropod functional groupnumbersin
theE.I.,isillustrated inaplot ofcanonical variabletwoversuscanonical variable one(Fig.3).
Allarthropod functional groupswereselected asimportant factors bystepwise discriminant
analysisfor discrimination amongthethreecategories (Table5).The first canonical function
separated thespeciespoorcategories 2and3from eachother (Fig.3);predaciousbeetlesand
linyphiid spiderswerepositively associated withdensevegetation andgranivorous carabid
beetleswerenegativelyassociatedwithdensevegetation(Table5).Inthesecondcanonical
function noneofthearthropod groupshad sufficient canonical loading;however, linyphiid
spiders contributedmosttothe separation ofcategory 1 from both categories 2and3,and
werenegatively associated with speciesrich vegetation.
can 1
Fig. 3.Plot of thesecond andfirstcanonicalfunctions discriminating among E.I. categories of the classification
'eispn/eicov'.Circlesrepresent theE.I. withplant species number >I2; squares represent E.I.withplant species
number <12and vegetation cover >80%;triangles representE.I.withplant species number <I2 and eicov<80.
Predacious carabid beetlesand linyphiid spiderswere>70%and>50%respectively more
abundant intheE.I.withfew plant speciesanddensevegetation (category 2)ascomparedto
othercatagories. Granivorous carabidswere>30%moreabundant inE.I.with speciespoor
andopenvegetation (category 3;'traditionalmanagement');also folivores weremore
abundant herebut didnotcontribute tothedistinctionsbetween thecategories becauseof
theirlownumbers(Table5).
42
Table5
Arthropod variables thatcontributed significantly toclassification of E.I. observations in 'eispn/eicov'categories
bystepwise and canonical discriminant analyses,standardised canonical coefficients, and mean valuesper crop
area category. Comparison of arthropod numbers inthecategories byDuncan's multiple range test.
Canlb
Mean values and multiple
Standardised Category 1:
eispn>12
coefficient
Variablesa
Predacious beetles
Granivorous carabids
Linyphiid spiders
Small staphylinids
Folivorous insects
Lycosid spiders
-0.92 c
0.52
-0.51
0.43
0.32
0.27
mean
26.7
3.1
35.0
9.5
1.1
3.1
b
b
b
b
b
b
Category 2:
eispn<12&
eicov>80
mean
47.2
a
2.9
b
60.2
a
10.3
b
0.8
b
4.3
b
-ange comparison
Categorj' 3 :
eispn<12 &
eicov<80
mean
22.6
b
4.2
a
39.3
b
11.1
a
1.7
a
6.1
a
(P<0.001)
(PO.001)
(P<0.001)
(P<0.1)
(PO.001)
(P<0.05)
"Variablesare listed inorder of selection by stepwise discriminant analysis.
b
Canonical function 1;responsible for 89%of thevariation.
c
Standardised coefficients >0.43 were considered large enough for interpretation.
3.4.Interactionsbetween distancetoE.I. andfarm category
Abundance oflycosid spiders,granivorous carabidbeetles and folivores were significantly
higher intheE.I.thaninthewheat (Table 6).Thedistribution of linyphiid spiders showeda
preference for thecrop area.Abundance ofpredacious beetles and small staphylinid beetles
didnot significantly differ between cropareaandE.I.(Table6).
Table6
Average numbers ofarthropodfunctional groups intheE.I.and inthe wheatcrop (30mfrom thefield margin).
Comparison of log-transformed values byDuncan's multiple range test.
Arthropod functional group
Predacious beetles
Lycosid spiders
Linyphiid spiders
Small staphylinids
Granivorous carabids
Folivorous insects
E.I.
12764
1636
17482
3922
1252
446
a
a
b
a
a
a
Crop area
13780
438
20174
5113
640
67
a
b
a
a
b
b
Significance
(NS)
(PO.001)
(PO.001)
(NS)
(PO.001)
(PO.001)
Highnumbers ofpredacious beetles andlycosid spidersintheE.I. coincided withhigh
numbers inthecroparea(Fig.4aand4b).Thedifferences inlinyphiid spiders (Fig.4c)and
granivorous carabid beetles(Fig.4d)weresimilar fortheE.I.categories 1('prototype farms')
and3('traditional management').However, thedifference ofthesespecieswasintheopposite
direction inE.I.-category 2(speciespooranddensevegetation):high linyphiid abundancein
theE.I.decreased towardsthecrop area,whileitincreased inboth other categories (Fig.4c);
granivorous carabidbeetles incategory2weremostnumerousinthecrop areaandleast
numerous intheE.I. (Fig.4e).Increased numbersof small staphylinidbeetles and folivores in
theE.I.didnot alwayscoincidewithincreased numbers inthecrop area (Fig.4eand 4f):
distribution patternsof small staphylinids wereveryvariable; folivore abundance intheE.I.
wasdifferent between categoriesbutwasgenerally lowinthecrop area.
43
B: lycosid spiders
A:predacious beetles
0.6
2
00
o
60
O
1.5
2 0.2
1
Om
30 m
Om
30 m
D: small staphylinids
C: linyphiid spiders
1.1
2 i
0.8
0m
30 m
Om
30 m
F: folivorous insects
E: granivorous carabids
0.8
0.3
0.6
0.2
0.4
o
-
0.2
0.1
0
0m
0m
30m
30 m
Fig. 4. Theabundance ofarthropodjunctional groups intheE.I. (0m)and in thecrop area (30 m). E.I.
categories ofselected classification 'eispn/eicov': Category I (squares)=species rich E.I. vegetation; category2
(triangles)= speciespoor and dense vegetation; category 3=(circles)speciespoor and sparse vegetation. Lines
between theaverages of arthropodfunctional group numbers('"log-transformed) aredrawn to illustrate the
differentpatterns among the threeE.I. categories and do notrepresent estimatedpoints inbetween thesampling
stations, (a)predacious beetles (b)lycosidspiders; (c)linyphiid spiders; (d)small staphylinid beetles; (e)
granivorous carabid beetles; (f)folivorous insects.
4. Discussion
4.1.Epigeicarthropodsinthecrop area
4.1.1.Observations comparedtothe hypotheses
Itwasexpected that organic duration, extensivecroprotation, areaofE.I.,andhigh spatial
densityofE.I.wouldrelatepositively withtheabundance ofpredacious and herbivorous
grounddwelling arthropods.Also,that organic duration and extensive croprotation would
relatepositivelytotheabundanceofdetritivorousepigeicarthropods.Allmentioned factors
indeedrelatedtodifferences intheabundance ofthearthropod functional groups involved in
44
the study.However only afew oftheobservations ofthedirection ofchangesof abundance,
wereinaccordancewith thehypothesis:lycosid spiders(whichwerethe least abundant
predaciousfunctional group) andgranivorouscarabidbeetlesshowed affinity for extensive
croprotation;predaciousbeetleswereassociatedwiththe farms withdenseE.I.
Mostobservationsdidnotcorrespondwithourhypotheses.Extensivecroprotations (farm N
andE)had alow abundance of (epigeic)detritivores,representedby smallstaphylinids.
Predaciousbeetles andlinyphiids,representing 84%ofallobserved epigeic arthropods inthe
croparea,didnotprefer extensivecroprotation,neither alargeE.I.areanoralongorganic
duration. Contrarytoexpectation,prototype farms whichhad alongduration, alargeE.I.area
andadensespatial arrangement ofE.I.,harboured comparatively lowabundanceofall five
predacious andherbivorous functional groups.
4.1.2.Smallstaphylinidbeetles
Contrarytoourhypothesis, anabundance ofdetritivorous staphylinids seemedtobe
associated with 'intensity' includingnotonlypercentage gramineous cropsbut also
interrelated management factors likemanure application, soilcultivation,weed controland
pest controlbyentomopathogens. Ambiguousbehaviour of staphylinidswithregardto
intensity, ascompared tootherlargeepigeic groups,isfound instudieswhichrelatetotillage
treatment (Heimbach &Garbe, 1996)andfarming systemscomparisons (Booij &Noorlander,
1992;Reddersen, 1997;Biichsetal, 1997).However,positive effects onstaphylinidswere
reported withregard tomanure(Bohac, 1999)andhousewastecompost (Idinger &Kromp,
1997).Inacomparisonoffour, long-durationorganicfarms inanoldculturelandscapeand
polder landscape,more staphylinidswere found inthepolderwhichrepresents anearlier
successional stageof soilcommunity (Smeding &Booij, 1999).
Ourobservations anddata from literaturemay suggestthat small staphylinid abundanceis
positively relatedtoacertain quantityoforganicmanure andfrequent soilcultivation. Small
staphylinidsmaytherefore notbeanappropriateindicator fortheaggregate functional group
ofsaprovorous arthropods (including also large Collembola andDiptera larvae);lowC/N
ratio andfibercontent oforganicmatterinputcould relatetodominancewithinthis functional
groupby smallstaphylinids.
4.1.3. Predacious beetles
Theobserved highest densitiesofpredacious beetles(mainlycarabids)werenot associated
with longorganicduration orextensive croprotation. Thisobservation iscontradicted by
severalfieldstudies inwhich carabidswere found tobe associatedwith lessintensiveor
organic crops(e.g. Booij &Noorlander, 1992;Holland etal, 1996;Basedow, 1991).Several
authorsreported that theunderlying factors whichpositively affected carabidswerecrop
coverandweeds,manure andless frequent soilcultivation(DenNijs etal., 1996;Hollandet
al., 1996;Booij &Noorlander, 1992;Idinger etal, 1996).Therefore itcouldbepossiblethat
the farm category 2withmoderately long-duration farms mighthavehad alower 'intensity'
(accordingtotheabovegivenwiderdefinition) thancategory 3withlong-duration farms;
category 3included former prototype farms whichhadproceeded further inoptimalisation of
intensivevegetableproduction. Wheatcrops in 1998offarm category 2hadrelatively high
weed densities,including Capsella bursa-pastoris onfarm EandPolygonumaviculareon
farm F,andtherewas anapparent abundance of springtailson farm F,although wedidnot
measurethese features. Onboth farms,therobust carabid speciesPterostichus melanarius
dominatedthecarabid community,whichwasalso found inthemostextensive systemsof
comparative studiesbyBooij &Noorlander (1992) andHolland etal.(1996).
45
4.1.4. Spiders
Superior dispersive abitilies of linyphiid spiders are stressed by several literature sources {e.g.
Sunderland, 1991; Halley et al, 1996). This could explain the observed positive association
with farms that have a low E.I. density. Both farms in Zuidelijk Flevoland had a long organic
duration but the polder is young (1968) which implies larger fields and also apossibly earlier
successional stage of the soil biocoenosis. Farm R is the most recently converted farm in the
study area and is situated centrally in a very open landscape part of Oostelijk Flevoland.
Abundance of linyphiid spiders might also indicate an earlier successional stage of the epigeic
community (that could be sustained in large scale landscape with less reinvasion possibility).
Accordingly, Idinger et al. (1997) observed most linyphiids in the inorganic as compared to
organic treatments.
In all the epigeic arthropod data there was anegative correlation between large organisms
(mainly carabids) and small organisms (mainly linyphiids). This suggested that intraguild
predation might influence functional group composition of ground dwellers. According to
Sunderland et al. (1996b) linyphiid abundance might be affected by predation.
Lycosid spiders were positively associated with extensive crop rotation. This was in
accordance with other studies which found that lycosids prefer organic above conventional
farms (Idinger et al, 1997) and belong to later stages of succession (Biichs et al, 1997). This
suggests that lycosids are the most vulnerable functional group among predacious ground
dwellers.
4.1.5. Ground dwelling herbivores
With regard to granivorous carabids, extensive crop rotation or lower 'intensity' was probably
correlated with (weed) seed availability. Several studies reported the relation between mobile
granivorous carabids and presence of weeds (De Snoo, 1995;Kromp, 1999). Folivores
seemed to be an insignificant group in the crop area and were slightly affected by 'intensity'
{e.g. weed control). The higher mid-field densities in less intensive systems observed by Hald
& Reddersen (1990) and Biichs et al. (1997) were collected by vacuum sampling or
emergence traps respectively, which might be more appropriate sampling methods for this
group.
4.2. Epigeic arthropods in the Ecological Infrastructure
4.2.1. Observations compared to the hypotheses
Our hypothesis was that improved E.I. would promote the densities of predacious and
herbivorous epigeic arthropod functional groups. However, observations did not provide
evidence for this hypothesis. The E.I. category based on high plant species number, included
the most succesful examples of improved E.I. This catogory involved the three former
prototype farms in Oostelijk Flevoland. In this E.I. all six investigated functional groups had
decreased densities as compared to other categories. Highest densities of ground dwelling
detritivore and herbivore functional groups were found in the E.I. category with presumed
adverse management ('traditional management' including a damaged sward).
4.2.2. Small staphylinid beetles
Although detritivores were not considered in our hypothesis with regard to the E.I.,
observations suggested that small staphylinids might be an important functional group in field
margins. Small staphylinid numbers were positively associated with 'traditional management'.
This observation suggests that staphylinids could be supported by the shredded and easily
decomposable litter of frequent cuts. In a field margin study in Zuidelijk Flevoland,
staphylinid density increased in the grass margins with 4 cuts per year as compared to crop
46
edges (Remmelzwaal & Voslamber, 1996). Accordingly, Canters et al. (1997) found that
staphylinids related positively to mowing frequency. Preference of small staphylinids to crop
as compared to E.I., observed in the 'prototypes' category (late mowing) was in accordance
with observations of Holland & Thomas (1996).
4.2.3. Predacious beetles
In improved E.I. in early summer, predacious beetles may be a relatively small component of
the arthropod community, because potential prey is foraging or resting higher in the
vegetation canopy. High densities of vegetation dwelling arthropods were found in improved
E.I. by means of vacuum sampling (Smeding et al., 2001b). Similar observations with regard
to predacious beetles were done by Haysom et al. (1999) in grassed headland; lowest
densities of carabids were observed in the uncut and 1cut per year sites as compared to 3 cuts
per year, field centre and unmanaged boundary sites. However, the highest predacious beetles
abundance were observed in tall and species poor vegetation. Interpretation of this abundance
may require a consideration of crop area influence.
4.2.4. Spiders
Linyphiid spider abundance in E.I. was difficult to interpret inrelation to E.I. characteristics
and probably requires consideration of interaction with the crop area density. Lycosid spiders
prefer sites with a warm microclimate (Remmelzwaal & Voslamber, 1996); this may explain
the observed positive relation to 'traditional management'.
4.2.5. Ground dwelling herbivores
Granivorous carabids and folivores showed positive association with the 'traditional
management' of frequent mowing without litter removal. With regard to the carabids this
might be explained by the occurence of annual species in open locally disturbed swards; these
plants have short life cycles, may have ascendant phenotypes and can provide seeds early in
the summer.
With regard to folivores more frequent cutting may improve the food availability near the soil
surface, because the vegetative stage of the vegetation is sustained by the inhibition of
flowering. Observations by Haughton et al. (1999), involving around 85%bugs and hoppers
(Hemiptera), showed a devastating effect on arthropod numbers by 1cut per year in the
summer as compared to 2 cuts per year in spring and late summer. In our study such a
devastating effect was not found, however folivore numbers captured by pitfalls indeed
showed a positive association with frequent mowing.
4.3. Comparison of Ecological Infrastructure and the crop area
4.3.1. Differences between E.I. and crop area
According to the hypothesis, lycosid spiders, granivorous carabids and folivorous insects
showed a higher abundance in the E.I. than in the crop area. However, abundance of the most
numerous functional groups (predacious beetles, linyphiid spiders and small staphylinids) did
not significantly decrease towards the crop. In the case of linyphiid spiders the opposite was
found, which corresponds to the observations of Holland & Thomas (1996) and could relate
to the dispersive abilities discussed above.
The E.I. crop area distribution pattern of linyphiid spiders, granivorous carabids and
folivorous insects on the farm-type with species poor and tall E.I. vegetation was significantly
different from distribution patterns found on the farm types with other E.I. traits. Mean
linyphiid numbers decreased towards the crop centre on this farm type, and mean numbers of
granivorous carabids and folivorous insects decreased less on this farm type than in other
47
farm types.Another apparent characteristic offarms with speciespoor andtallE.I. vegetation
wasthelowabundance ofsmallstaphylinids inboth E.I.andcroparea.
Apossible explanation oftheseobservations on linyphiid spiders,granivorous carabids,
folivorous insects and small staphylinid beetlesmayinvolvetheabundance ofpredacious
beetles.Predaciousbeetleshadthehighest abundance inthecrop areaoffarms with species
poorandtallE.I.vegetation. Thishighpredaciousbeetleabundance inthecrop areacould
haveinterfered withtheabundanceofsmall-organism epigeicgroups.Accordingly, inthe
wholedatasetamarginally significant negativecorrelation was found inthecrop area
betweentotalnumber/farm ofcarabidbeetles andtotalnumber/farm ofpooled linyphiidsand
small staphylinids (Pearsoncorrelation coefficient =-0.61, PO.0105). Interaction between
predaciousbeetles andlinyphiid spidersmayinvolve'intraguildpredation'(Sunderland et al,
1996b).Theabovementioned increased abundance ofherbivores (i.e.granivorous carabids
andfolivorous insects)incropswith abundant predacious beetles,couldindicate acauseas
wellasaneffect ofpredaciousbeetleabundance:
- herbivorous functional groupsindicatethe suitability ofthecrophabitat (weeds) for
herbivorywhich involvesincreasedprey availability for theground dwelling beetles
(Booij &Noorlander, 1992);
- predaciousbeetlesreducepredationpressure onherbivoresbyinterfering with predators
thatcanmore effectively hunt inthecanopy(e.g. spiders)whereascarabidsprefer tohunt
atthe soil surface (Kromp, 1999).
4.3.2. Indicationsfor dispersivemovements betweenE.I. andcrop area
Onlylycosid spiderdistribution suggested thattheE.I.couldbearesource for croparea
populations,becauseE.I.populationsweregenerally much largerthancrop areapopulations
andthelycosidabundance inE.I.wascorrelated tolycosid abundance inthecroparea.
HighnumbersofpredaciousbeetlesintheE.I.werealsoassociated withhighnumbers inthe
croparea.Accordingly, inthewholedatasetasignificant positivecorrelation is found
betweentotalnumberperfarm of carabidbeetles inthecrop area andtotalnumberper farm
intheE.I.(Pearson correlation coefficient =0.72,P<0.05).However, highnumbersof
predaciousbeetlesinbothE.I. andcroparea,couldbebetter explainedby crop areatraitsthan
byE.I.traits:thegroupoffarms (farms A,F,E)with speciespoorandtallE.I.vegetation
overlapped withthegroupof farms witharelatively 'extensiveproduction' inthecroparea
(farms F,E).Forthislattercategoryitcouldbearguedthat predacious beetleswere enhanced
inthecroparea.Whereas for theformer categoryexplanationwasdifficult becausetheE.I.
represented anintermediate E.I.typepossessing avegetation coverorplant speciesnumber
similar tootherE.I.types.Anadditional argument fortheassertion that crop areatraitsand
not E.I.traitsdetermined thehighpredaciousbeetlenumber, isthat crop area sizeexceedsthe
E.I.sizeandmaytherefore includealargeramountof food for epigeicpredators than theE.I.
Sincepredaciousbeetlesaremobilespecies(Thomasetal, 1997),theymay easily dwell
from cropareatoE.I. andviceversa.
Observations oflinyphiid spiders,amobilespecies,alsosuggested that abundance intheE.I.
mightbedeterminedbycroparea abundance.High abundance inthecrop areawas associated
withhighabundance intheE.I.However,thehighest abundance intheE.I.(speciespoorwith
tallvegetation)wasnotrelated toahighcropareaabundance.This divergent situation might
havebeenduetohighcarabid abundance inthecroparea,asexplained above.
Withregardtothedistribution of small staphylinids inE.I.andcrop area,observations didnot
indicatedispersivemovement. Apparentlyhigh levelsinboth E.I.andincrop areawere
associatedwith lowlevelsinadjacent habitat (cropareaorE.I.respectively).High abundance
48
ineachhabitat werepossibly related tolocalhabitat factors, assuggested earlier inthispaper:
flailmowing inE.I.andintensive cropmanagement inthecroparea.
SincetheimprovedE.I.vegetationdidnotharbourhighabundanceofepigeic functional
groups,itcouldnotbeidentified asaresource for epigeic arthropods inthecrop area.This
observation andalso indications ofeffects onabundance intheE.I.bypopulations inthecrop
area(withregard topredaciousbeetlesandlinyphiid spiders),areseemingly contradicting
reportsonenhancing effects onarthropods of(improved) E.I.vegetation.However, these
reports areoften dealingwithwinter shelter andsubsequent dispersion ofarthropods inspring
(references reviewed inDeSnoo&Chaney, 1999).Itmightbepossiblethat enhancing effects
ofE.I.cannotbeobserved inthe summer,becauseepigeic arthropods have already left their
shelter. Subsequentlytheirnumberatthefarm-level mightbedeterminedbycroparea
resourcesofinitiallydetrital and latermixed detrital/herbivoreorigin.However availabilityof
shelterprovidedbyE.I.duringwinter andspringmaystillaffect thetotal farm-level numbers
(Lys, 1994;Lys&Nentwig, 1992).Thisexpectationwassupportedbyobservations(inthe
discriminant analyses above) ofthepositive effect of spatialdensityofE.I.onpredacious
beetles.However,thiseffect maynotbeobservable inacomparison ofE.I. andcroparea
numbers.
4.4. Conclusions
Comparisonofepigeicarthropod functional groupsoneightorganicarablefarms suggests
thatthe'intensity'ofthecropareaisamajor determining factor. Theconcept of'intensity'
shouldnotonlyaddresspercentage gramineous cropsbut also,for example,manuring and
soilcultivation. Length oforganicdurationbyitselfmayprovidenoclearbasis for
distinctionsbetweenthefarms becauseofdifferences in'intensity' amongthe long-duration
farms. Interpretation offieldobservationsdeliniatesthreemoreorlessdistinct functional
groupcompositions inthecroparea:
- relatively high abundance ofpredaciousbeetles(mainly carabids),lycosid spiders,
granivorousbeetlesandfolivores incrop areaswithcomparatively low 'intensity';
- relatively highabundance of small(fungivorous) staphylinids incropareaswitha
comparatively high 'intensity';
- relativelyhigh abundanceoflinyphiid spidersincropareaswhichrepresent anearlier
successional stageduetorecentconversion ortolandscape factors.
TheareaandqualityofEcological Infrastructure provided noclearbasis for distinctions
between thefarms. Summer abundance inE.I.ofdominant ground dwellinggroups,
predaciousbeetles andlinyphiids,mightbedeterminedbycropareaconditions. Traditional
management ofE.I.,thatwas expectedtobeadverse,showedtohave aqualitatively different
epigeic community andmaypositively supportlycosid spiders,small staphylinids andepigeic
herbivores ascompared toothermanagement. Potential increaseofarthropod abundancein
latemownE.I.maynot involvegrounddwelling arthropodsbutinvolvevegetation dwelling
arthropodsthatoccurinahigherstratumofthevegetation.
Increased abundanceofpredacious speciesisnot equaltothecapacity ofthecropping system
tocontrolherbivorouspests(e.g. Wood&Lenne, 1999).Low epigeicpredator abundance(as
observed inthe'prototypes') could indicateboth asufficiently balanced system, inwhich
predatorsinhibit initialpestdevelopment, aswell asapestoutbreak susceptible system.
Conversely highpredator abundancemaypositively correlate withhighherbivorouspest
densitiesbecausethesepredatorsmighthavebeen supported byabundant prey.Highnumbers
ofpredatorsmayindeedrepresentpestcontrolpotentialiftheywould developon
detritivorousprey (Wiseetal, 1999)ornon-pestherbivorousprey(e.g. Andow, 1988;
49
Altieri, 1994)and subsequently depresspestpopulations.Tobringclaritytothis subject
further investigations areneeded.
4.5. Recommendations
Comparative studiesonground dwellingarthropod functional groupswouldbenefit from a
further restriction ofgeographical variationbetween farms. Definition of'intensity' shouldbe
based onmore farm characteristics thanonlycroprotation intensity. Ourexplorative studies
mightberepeated with emphasisonthreeextremefarm types:recently (1-2years) converted
farms, longorganic duration (>8years) and'intensive'cropping, andlongorganic duration
extensivecropping {e.g. >35%gramineous crops,including leys).Becausethe latter category
isincreasingly rareincommercial organic farming, farm experimentsmaybeneeded,
particularlywheninvestigating theeffects ofincreased detrital input assuggestedbyWiseet
al.(1999).
More specific researchthemesmayaddress;
- theecologyoftheaggregate functional group ofsaprophorous arthropods including
staphylinids,Diptera, andCollumbola(e.g. Weberetal.,1997;Idingeretal.,1997);
- theimportanceofintraguildpredation incrops(e.g. Tscharntke, 1997);
- theeffect ofdifferent mowingregimesonarthropod communities (e.g. Haughton etal.,
1999),including vegetation dwelling functional groups aswell aseffects ofpredation
pressure intheE.I.duetoepigeicpredators supported byrichresources inthe croparea.
Additional attention shouldbepaidtotheoften abundant butpatchilydistributed ants
(Formica), becausethis speciesmaycompetewithotherpredators andmayprotect aphidsand
related speciesinfieldmargins.These studiesshould extend toalargerpartofthe farm food
web,whichmightbenecessary for soundlybasedpractical recommendations with regardto
enhancing farm biodiversity and itspotential ecosystem services.Although nofirm
conclusionscanbedrawn yet from thisfieldstudy,wethinkthat results indicate future
perspectives ofafood webapproach on farms.
Acknowledgements
Theauthorswishtothankthefarmers whoallowedus accesstotheirland.Thanks aredueto
AndreMaassen (Unifarm-WUR) for technical assistance,BertusMeijer, Bart Venhorst and
JanNoorlander (PRI)for arthropodmeasurements andArienavanBruggen for her statistical
help.Thework atWageningenUniversity isfunded bytheMinistry ofAgriculture,Nature
Management andFisheries,Department of Science andKnowledge Dissemination.
50
Chapter 4:Insectivorous breedingbirds onorganic farms in
relation tocroparea,ecologicalinfrastructure and arthropods
F.W. Smeding3&C.J.H. Booij"
"DepartmentofPlant Sciences, Biological Farming Systems group, Wageningen University, Wageningen,
TheNetherlands
Plant Research International, Wageningen, The Netherlands
Abstract
Hypotheses onthe relation ofarthropod functional group abundance, crop area and ecological infrastructure
(E.I.) variables tothe territory density offunctional groups of insectivorous birds were tested on organic arable
farms. Bird territories were mapped onorganic arable farms (eight in 1998,when epigeic arthropod were also
studied, andnine in 1999,whenvegetation dwelling arthropod studies wereincluded). The farms were all
situated in an open landscape dominated by agricultural landuse; skylark, linnet and meadow pippit were the
most numerous species. Most birds were more strongly related tovegetation dwelling arthropods in 1999,
particularly those in the E.I., than toground dwelling arthropods in 1998.The density ofbird territories could
usually bepredicted by a combination of crop area and E.I.variables, including positive relations to improved
E.I. characteristics. In 1999,according tothehypotheses, positive relations to organic farming duration were
found; however inboth years a general negative relation to extensive crop rotation was found. It willbe
discussed asto whether intensively managed crop areas may supportbirds due totheperiodic and localised
herbivore increases ina crop mosaic,but also whether extensively managed crops might offer lessprey items
due totheherbivore control exercisedby epigeicpredators aswell asaless susceptible cropphysiology. Late
mown E.I.might possibly offer animportant food resource thatmay supplement the,often interrupted, food
resources ofthe crop area.
1.Introduction
1.1. Biodiversitylossin agriculture
Aseriousdeclineofthepopulation invariousplant and animal speciesonmore intensively
farmed land inindustrialised countries,hasbeen shownby, for exampleFuller etal.(1995)
andAndreasen etal.(1996).Thisdecline concernsnotonlyecologists and agriculturists,but
alsothewiderpublic(Paoletti, 1999;Wood &Lenne, 1999).Thedevelopment ofmultispecies orsustainable farming systems isprobably neededtoreversethistrend (Vandermeer
etal, 1998;Altieri, 1994, 1999;Almekinders etal, 1995).Suchfarming systems utilise
ecosystem servicesprovided bybiodiversity (e.g. pest control, soil fertility), and allowa
greater chance for natureconservation centeredbiodiversity. Several examples ofmultispecies farming systempractices aregivenbyAltieri (1994),Wood &Lenne (1999) andother
authors.
Development ofmulti-species farming systemsmayrequirespecific research approaches.
Firstlytheresearch shouldtakesite-specificity ofbiodiversity into account (Vandermeeret
al.,1998)and shouldpreferably start from 'nearlynatural systems'(Brown, 1999a).Secondly
thevariables, should specifically addressthe farm-, orhigher levelsof aggregation
(Almekinders etal.,1995).Thirdly thepredictorvariables shouldclearlyrelatetodecisionsin
the farm management (Vereijken, 1997;Kabourakis, 1998;Smeding &Joenje, 1999;Park&
Cousins, 1995).
51
1.2.Organicfarms andecologicalinfrastructure
Organic farms that adheretotheproduction guidelines2092/91 oftheEC (Anonymous, 1991)
aresuitableresearch objects asthemaintenance andutilisation ofbiodiversity isinherentto
thephilosophy oforganicfarming. Research showsthatorganic farming whencomparedto
conventional farming, involvesagreaternumber anddiversity of species andhabitats for
birds,vegetation dwelling arthropods, epigeic arthropods,earthworms and arableweeds(e.g.
Kromp&Meindl, 1997;Paoletti, 1999;VanElsen,2000;Smeding, 1993;Hendrikset al,
2000).
Becauseoftheirincreased similarityto'nearlynatural systems' farms that combineorganic
croppingwith adeliberately enlarged, spatiallydiversified ecological infrastructure areof
particularinterest (Brown, 1999a).Inthisarticle ecological infrastructure (E.I.) isdefined as
thetotalofsemi-natural (aquatic,woody,tallherb andgrassy)habitats onthe farm including
theirspatialarrangement (Smeding &Booij, 1999).Enlarged and diversified E.I.enhances
thenumbersanddiversity ofindigenousplants andanimals atthefarm level (e.g. Joenjeet
al, 1997;Boatman etal, 1999).Thiscouldcontributetosoil fertility andpest controlon
organic farms (Brown, 1999b;Kromp &Meindl, 1997;Theunissen &Kohl, 1999).
1.3. Foodweb approach
Recent advances inresearch of food webs(Polis&Winemiller, 1996;Pimm, 1991)offer an
appropriatemethodology forbiodiversity research, addressingvariables athigher levelsof
aggregation.Theseadvances,including somestudiesinagricultural habitats (e.g. DeRuiteret
al., 1995;Tscharntke, 1997),areproviding inspiring examplesofhow(agro) ecosystems can
beapproached athigher integration levelsthan thespecies level.Someofthisresearch
indicatesthat farm food webscanmediatetheeffects ofenvironmental factors on species
(Wiseetal., 1999;Tscharntke, 1997).
Ourgeneralhypothesis aboutthe farm food webonorganic arable farms withimproved E.I.
isbasedonthree sub-hypotheses:
Firstly,increased organicmatter inputsfromorganicmanure,cropresidues,cereals,ley
pastures,andcompost,relatetoincreasednumbers ofinvertebrate detritivorous meso-and
macrofauna (e.g. Pfiffner &Mader, 1997;Weberetal, 1997;Idinger etal., 1996;Heimbach
&Garbe, 1996).Secondly,thenumbersofvariousnon-pest herbivorous functional groupsare
increasedbyimproved E.I.(Holland &Fahrig, 2000;Boatman etal, 1999)but alsoby
organic cropcharacteristics (Hald&Redderson, 1990;Moreby &Sotherton, 1997).Thirdly,
combined increasesofdetrital andherbivore invertebrates relatetoacumulative positive
effect onthehigher trophic level,includingbothinvertebrate andvertebrate predators,which
feed onpreyfromboth detrital andherbivore subsystems (e.g. Wiseetal, 1999;Idingeret
al, 1996).
Itislikelythat succession toahypothetical farm food webrequirestime(Idinger etal, 1997;
Edwards etal, 1999),possibly atleast thelength ofoneortwocroprotations.The succession
speedmaybenegatively influenced byprevious applications ofpesticides andthedepletion
oforganicmattercausedbyreliance onartificial fertilisers (e.g. Paoletti, 1999).
52
1.4. Insectivorousbirdsandarthropodpreyavailability
Thecurrentfieldstudy was focussed onthe abundance ofinsect-feeding birdsinrelationto
croparea,E.I.characteristics andabundance ofarthropod functional groups. Associated
studies,tobepublished elsewhere,weredevotedtolowertrophiclevelsofthefarm foodweb,
includingboth vegetation andground dwelling arthropods(Smedingetai, 2001a,b).The
guild ofinsect-feeding birdsrepresents ahighertrophic levelthatmaybeenhancedby
productivity atthebaseofthefood web(accordingtotheconcept ofOksanen etai, 1996),
andtherefore reflects the'ecological carryingcapacity' ofafarming system (Braaeet ai,
1988).Birds,andtheirpreyorganisms, areinfluenced by farm characteristics.Birdsare
therefore affected bothdirectly andindirectly byfarm traits.Theseindirect effects onbirds
areprobably mediated throughthe food webonthe farm (e.g. Tscharntke, 1997).
Bird abundanceonfarms isnot onlydetermined by foodbut alsobyother environmental
factors (ascomprehensively outlinedbyAndrewartha &Birch, 1984).Importantphysical
factors actingon farmland birdsmaybedisturbance andnest destructionbymachinesor
trampling (e.g. Green, 1980),availability of songpostsornest sites(Stoat, 1999),weather
conditionsorinaccessiblevegetation (e.g. Schekkerman, 1997).Spatial features like field
size,cropdiversity androtationmaynotnecessarily relatetofood distribution.Howevermost
studiesonfarmland birdsindicatethat food availability isamajor factor determiningbird
density(reviewedbyPoulsen etai, 1998).Bird chicks areparticularly vulnerableto shortage
ofproteins supplied bytheirinvertebrateprey(e.g. Hald&Reddersen, 1990;Aebischer,
1991;Poulsen etal, 1998).
Comparative studiesbetween organic andconventional farms (Braaeetal.,1988;Hald&
Reddersen, 1991;Wilson etal.,1997;Chamberlain etal.,1999;Moreby &Sotherton, 1997)
emphasized the effects ofpesticide usageon food availability,becausepesticides depressed
bothpreyandhostplantsofpreyonconventional farms. Contributionsofother farm
characteristics affecting invertebrates weredifficult toassessbecausemost studied factors
werecorrelated withpesticide application. However, Braaeetal.(1988)traced apositive
effect ofmanure/fertilizer on8of35numerouslyoccurringbird species;Hald&Reddersen
(1990)revealed thepossible importance ofhostplantsofFabaceae, Cruciferae,
Polygonaceae, which arecommononorganic farms ascroporweed. Chamberlain etal.
(1999)detected effects ofdifferent landscape structures,whichmightbemorerelevantto
organic farming practices (Hendriksetal, 2000)onthebird community.
Traditional farming systemsmayrevealthekeyposition offood resources for rich wildlife
(e.g.ofdehesas;Edwardsetal, 1999);inTheNetherlands atraditional(i.e.orthodox
biodynamic) mixed farm of8ha,possessed territories ofendangered bird species,red-backed
shrike(Lanius collurio)andortolanbunting (Emberiza hortulana),probably dueto increase
ofspecific preyitems(Esselink etai, 1996).
Autecological research on farmland birdsgreatlycontributed todeepening the understanding
oftherelationbetween cropmanagement andchick food availability. Inparticular,workon
greypartridge (Perdrixperdrix) (e.g. Rands, 1985) andskylark (Alaudaarvensis) (e.g.
Wilson etai, 1997;Poulsen etai, 1998;Wakeham-Dawson etal, 1998)involved detailed
investigations ofhabitat selection,nesting success,diet andchick condition inrelationto farm
characteristics andarthropod abundance.These studies wereabletorelate starvation ofchicks
and lowterritory densitiesto apparant food shortageinthebreedinghabitat (e.g. Poulsenet
al, 1998).
53
Arthropod functional groups,central toourresearch,includepreyitemsforbirds,butmany
taxamaybeinsignificant becauseofsize,digestibility,repellant tasteorother characteristics
assummarizedbytheconcept 'availability'. Consequently farmland birdshave distinctive
preferences. Inour explorative studywechosetorelateinsectivorousbird-density tothe
abundanceofentirearthropod functional groups.Contrarytoe.g. Morebyetal.(1994)and
Poulsenetal.(1998)whoselected 'chick-food'withinarthropod samples,according todiets
ofconsidered birds.Ourresearch, therefore, doesnotdiscernbetween direct feeding relations
andshared indirect association withcertainhabitat factors. Distinguishing different bird
functional groupswithknownspecific food andhabitatrequirements improvesthebasis for
interpretation withregardtopossible causal factors. However,thisresearch wasprimarily
concernedwithrelatingbird functional group abundance (determined byits specific food with
emphasisonchickdiets)toarthropod functional groups (indicatingthe farm food web
structure)inanattempt tolinkautecological research(e.g. Poulsen etal, 1998)to farming
systemsresearch(e.g.Swift &Anderson, 1993; Vereijken, 1997;Wolfert, 1997;VanKeulen
etal, 1998).
7.5.Hypothesesandobjectives
Fivefunctional groupsofbirdsfeeding oninvertebrates areexamined.Thedistinctionis
basedondifference inadultdiet (insect,mixedinsect-plant/seed orsoil life) andhabitat
preference (field orfield margin).Foreachgroup,specific hypotheses werederived from the
above-explained generalhypothesis withregard tothefarm foodweb.
1.5.1. Insecti-granivorous birdswithfieldaffinity
Thesebirds feed onthegroundonplants.Theywereexpected tobe supported byground-and
vegetation dwellingdiurnal predators andherbivores inthecrop area.Farm management
features whichwereexpected toenhancethepopulation ofthesebirdswere areduced number
ofmachineoperations (whichdisturbtheirnests) andtheoccurrenceofcerealcropsand
weedswhich supplyarthropods andseeds.Therefore extensivecroprotationswere expected
tofavour thisgroup.Thisgroup isrepresentedbytheskylark (Alaudaarvensis)whichis
knowntofeed itschickswith largespiders,carabidbeetlesand largesized herbivores (sawfly
andlepidopteran larvae,beetles).Youngchicksreceiveboth smalland large soft-bodied
insects,for exampleherbivorous larvae,andolderchicksreceivemore largehard-bodied
insects,for examplebeetles(e.g. Wilsonetal, 1997;Poulsenetal, 1988).Skylarksare
particularly attractedbygrass leys(set-aside) andspringcereals.Theyprefer opencropsto
forage, andavoiddensecrops.
1.5.2. Insecti-granivorous birdswithE.I. affinity
Thesebirdswereexpected tolookfor theiranimal food inthevicinity oftheir seedresources
atthesoil surface, onplantsintheE.I.andincropedges.Herethesebirdsfindground living
andvegetation dwellingdiurnalpredators andherbivores.Farmmanagement features which
wereexpected toenhancethisgroupwerethe amountofE.I.onthe farm, thetiming ofE.I.
cutting andthevariation ofE.I.vegetation, including fruiting dicots.These factors would
mainly influence theirfood availability sincenests areusuallynot locatedin herbaceous
vegetation.Thisgroup ismainlyrepresentedbythelinnet (Carduelis cannabina), which feeds
itschickswithinvertebrates toavarying extent,captured ontheground aswell asonplants;
chick dietsincludebeetles,spiders,fly adult and larvae,andcaterpillars,but alsosmall
herbivores likeaphids(Cramp, 1988).
54
7.5.3.Specialistinsectivorous birdswithfield/E.I. affinity
Thesebirds areabletocapture flying insects.Therefore theirdensitywas expectedtorelateto
thenumber ofvegetation dwelling diptera,whichdominatetheairborne arthropod
community;thesediptera aremainly adultsofdetritivorouslarvaeand (root)herbivorous
larvae{e.g. Tipulasp.).Probably toalesserextent,thegroupwouldbesupported bynumbers
ofvegetation dwellingpredators {e.g. syrphids)andfolivorous herbivores.Farm management
factors thatwereexpected tofavour field-inhabiting insectivorousbirdswouldbe organic
duration andextensive croprotation becausethese factors werepresumedto supportthe
detrital food web.Alsotheamount andquality ofE.I.wasexpected toinfluence fieldinhabiting insectivorousbirdnumbers,becauseadultsofmany flying insects from various
trophicgroups areattractedby flowers intheE.I.Thisgroupisrepresented bythe
Motacillidaespeciesincludingwagtails{Motacilla sp.)andmeadowpipit {Anthuspratensis).
Wagtailsareknowntofeed onflies andmidges,including smallindividuals from 1-2 mm,
but alsoonbeetles(carabidsaswell asherbivorous species) (Cramp, 1988).Meadowpipit
adultsseemtofeed onsmallpredominantly dipteraninsects (<5mm)(Cramp, 1988)andare
often seentoforage onthegroundbeneathcropcanopies.However chicks areoften tobe fed
with large(>1cm)soft larvae(Cramp, 1988),that aregenerallyherbivorous.Pipits onarable
farmsmostlyoccurinfieldmargins(Scharenburg etal, 1990).
1.5.4. Specialistinsectivorous birdswithE.I. affinity
Thesebirds feed onvegetation dwelling arthropods ofvarioustrophicgroupsintheE.I.and
areexpected toprefer quantity(height andcover)abovequality {e.g. speciesrichness)ofE.I.
vegetation. Theamount ofE.I.(boundarywidth, areaandspatial density)might contributeto
thedensityofthesebirds(Stoat, 1999).Thisgroupismainlyrepresentedbyreedwarbler
{Acrocephalusscirpaceus) andreedbunting {Emebriza schoeniclus).Innorthern claydistricts
inTheNetherlands,dominatedbyarable farming, abundance ofbothbirds isclearlyrelatedto
thelengthofditcheswithold (>1year)reed stands (Scharenburg etal, 1990).Ditchesin
Flevolandwith amowingregimepromotingreed growthwererapidly colonizedbyreed
warbler andalsomarshwarbler (Remmelzwaal&Voslamber, 1996).Dietsinclude awide
rangeofarthropodtaxathatcanbefoundwithinthisvegetation (Cramp, 1988).
1.5.5. Soillife-feedingbirds
Prey itemsofsoil-life feeding birds includemainly soilmacrofauna, including detritivores
(earthworms) androotherbivorous insect larvae (particularly Tipulasp.)and additionally
epigeic arthropods (carabidbeetlesand spiders).Open fields without vegetation orwith
sparseorvery lowvegetationprovidebest accesstosoillife.However, fields thatremain
openduring springand early summer,receiveintensive farming procedures that disturb
nesting.Thegroup ismainlyrepresented byLapwing {Vanellus vanellus).Food availability
for lapwing chicksisoften critical becauseofagriculturalpractices.Dry soil isharderto
penetrate andlimitstheaccesstosoilmacrofauna. (Schekkerman, 1997;Beintemaet al,
1991,1995).
1.5.6. Insecti-granivores versusspecialistinsectivores
Withregardto food requirements ofcombined groupsofinsecti-granivorous and specialist
insectivorous birds,ourhypothesis wasthattheinsecti-granivorous groupwill showaclearer
relationship with grounddwellling arthropods (sampled bypitfall traps)than specialistbirds.
Furthermore,weexpected thatvegetation dwellingpredatorswouldbethemost important
common food resourceofthe four functional bird groupsbecause oftheirgenerally larger
size.Totalbirddensityisexpectedtoberelatedbothtothis groupofvegetation dwelling
predators aswell asto farm characteristics that favour detrital webnumbers{i.e.duration,
extensive croprotation) andflowers/seeds intheecological infrastructure.
55
1.5.7. Landscapeeffects
Birdsmaybeaffected bydifferences intheterrain.Forexample,inthenorthern clay district
inTheNetherlands, skylark,blue-headed wagtail,meadowpipit andquail(Coturnix coturnix)
prefer openterrain.Marshbird abundance is favoured bycontinuousreedhabitat of 1.5-3 km
length(Scharenburg etal, 1990).Therefore alsolandscape differences between farms were
takeninto account.
1.5.8. Objectives
Thus,theobjectives ofthisstudywere:
1. todeterminetheterritory densityofinsectivorousbirdsoforganicfarms, andrelatethis
densitytotheabundanceofarthropod functional groups;
2. torelatetheterritory density ofinsectivorousbirdsoforganic farms totheextentofonfarm ecological infrastructure, andvegetation andcrop characteristics.
w
20 Kilometers
Fig. 1.Study area in 1998-1999:five farms withbirdand arthropod studies in 1998as well as 1999are
represented bysquares; onefarm with birdandarthropod studies only in 1998isrepresented by across;two
farms with birdand arthropod studies in 1998and onlybirdstudies in 1999are represented by circles; two
farms withbirdand arthropod studies in 1999arerepresented by triangles.
56
2. Materials and methods
2.1. Study area
Thestudywascarried outonorganic farms intheprovince ofFlevoland, TheNetherlands.
Thefarms arelocatedinthethreepoldersNoordoostpolder, Oostelijk Flevolandand Zuidelijk
Flevoland (Fig. 1).Thesethreepolderswerereclaimed around 1940, 1957and 1968,
respectively, and aredominatedbyagricultural landuse.Thelandscape isvery flat andopen
withwood lotsconfined to farmyards, villagesandmainroads.Thesoilisacalcareousclaysandyclayofmarineorigin.Flevolandwaschosenasourstudyareabecauseithasa
concentration oforganic farms that aresimilarwithrespecttotheirhistoryandtopography.
There arecurrently 75economically viableorganic arable farms inFlevoland,which are
generally large(c.30-70ha)andintensiverelativetootherorganicarable farms inEurope.
TableI
Characteristics of thefarms, ecological infrastructureand landscape (200ha, including thestudied farm).
1998
Level
Variable
Abbrev.
A
N
T
F
Farm
n year organic farm (n)
12
12
8
Farm
Cereals and ley pasture (%)
DUR
INT
59
Farm
Farm
% of crop area within 100 m range E.I. (%)
38
74
Semi-natural habitat (E.I.) (%)
EI100
AREA
38
47
7
24
E.l.
Mowing date (farm level) (month)
Mowing frequency (n/year)
MOW
7
5
9
5
E.I.
MOWFRQ
2
3
1
2
E.I.
Height vegetation (m)
EIGHT
E.I.
Cover vegetation (%)
EICOV
1.8
98
1.1
82
1.8
97
1.0
88
E.I.
Species diversity vegetation (n/4 m2)
Dominant species diversity (n/4 m 2 )
EIDOM
12
3.4
8
2.8
11
3.4
9
E.I.
Landscape
Age polder (year)
LSAGE
41
41
Semi-natural habitat landscape (%)
Cereals/ley pasture landscape (%)
Vegetables landscape (%)
8
44
5
32
5
Landscape
Landscape
LSNAT
LSINT
30
4
34
30
Landscape
LSVEG
38
23
17
Farm
n year organic farm (n)
DUR
13
Farm
Cereals and ley pasture (%)
13
24
32
Farm
Weed abundance (class)
INT
WABUN
Farm
Farm
% of crop area within 100 m range E.I. (%)
Semi-natural habitat (E.I.) (%)
Ell00
AREA
E.I.
E.I.
Mowing date (farm level) (month)
Mowing frequency (n/year)
E.I.
E.I.
Height vegetation (m)
Cover vegetation (%)
E.I.
E.I.
Species diversity vegetation (n/4 m2)
Dominant species diversity (n/4 m 2 )
EIDOM
Landscape
Age polder (year)
LSAGE
2
EISPN
40
1
2
L
E
1
10
4
8
18
11
70
35
51
2
80
3
90
5
72
4
5
6
3
0.7
2
6
2
2
0.7
92
97
10
3.0
10
3.4
15
41
41
41
57
4
7
4
26
5
27
23
27
16
29
22
51
21
K
Z
74
1
R
85
6
2.3
3.1
1.2
1999
MOW
MOWFRQ
EIGHT
EICOV
EISPN
2
0.4
2.3
9
1.2
1
2
11
42
3.9
33
1.8
18
12
20
66
1
8
16
47
40
74
74
72
2
1
2
1
2
7
2
1.8
5
3
1.1
9
1
5
3
1.0
3
0.7
98
12
3.4
31
82
8
2.8
31
1.8
97
U
3.4
42
88
9
3.1
42
5
84
9
2.8
42
1.3
5
2
0.4
82
8
2.5
42
2.3
2.3
2.4
80
80
90
1
3
5
5
7
2
0.7
3
0.7
6
85
92
2
1.2
97
6
10
10
2.3
42
3.0
42
Tenfarms were selectedbased ondifferences infarm structure andecological infrastructure
(E.I.)traits(Table 1).Theselection includedninecommercial organic farms andone
experimental farm. Theselected commercial farms areallarablealthough three(farmsN,T,
andK)possessastablewithlivestock fedonfodder cropsfrom thesamefarm but grazing
57
5
72
3.4
42
D
7
1.1
94
3.8
28
elsewhere duringthe summer. Theorganic experimental farm ofWageningen University isa
mixeddairyand arable farm. Fourcommercial farms (A,T,LandD)wereEcological Arable
Farming Systems (EAFS)prototype farms during 1992-1997(Vereijken, 1997, 1998).Among
thesefarms, farm Aisdifferent becauseitissituated intheyoungest polder Zuidelijk
Flevoland,andjoined theEAFS-project afew years laterthantheothers.FarmsAandN
startedin 1985onanexperimental reclamation areawherepesticideshadneverbeenused
(Remmelzwaal, 1992).
Bird and arthropod studies in 1998involved 8farms (total 542ha)inthreepolders (Fig.1).
Bird and arthropod studies in 1999involved 7farms (total 392ha)thatwereconfined tothe
polder Oostelijk Flevoland. Ontwofarms inpolderZuidelijk Flevoland (farms AandN;216
hastudy area)onlybird studiesweredonein 1999.
2.1.1. Croparea characteristics
Theorganicduration oftheselected farms ranged from oneto sixteenyears (Table 1).
Ploughing isgenerally at25-30cmdepth.Onall farms a6-7yearcroprotation is maintained,
with 6-14 different cropsper farm. Theproportions ofdifferent typesofcropper farm ranged
inboth yearsfrom 10-70%for gramineous crop (cereals and leypastures), 10-28%for
traditional lifted crops(potato,beet) and20-11% for vegetables (mainlyonions,peas,sweet
corn,variouscabbages,redbeet andrunnerbeans).
Thefarms with themost intensive croprotationshad upto60%vegetables and therefore a
lowpercentageofgramineous crops (cereals,leypasture).Ascompared toothercrops,
gramineous cropsprovide alarge amount ofcarbonincropresidues andrequire fewer
proceduresthat causesoildisturbance.Becauseinput ofnutrients (N,P,K)hastobe adjusted
tocroprequirements,andvegetables needmorenutrientsthancereals,intensity ofcrop
rotation isassumed torelatetoboththeamount ofcropresidues andtheamount ofNapplication atthefarm level.
2.1.2.Ecologicalinfrastructurecharacteristics
Canals andbanks (together c.3-4mwidth)that arelaidoutaslinearherbaceous boundaries
adjacent tothecropsmainlydetermine theecological infrastructure (E.I.)ofarablefarms in
Flevoland. Onfive farms,boundaries arewiderbecauseofadjacent (2-3mwide) grassstrips,
often including clovers(Trifolium spp.),ononeorboth sidesofthecanals.Farm Ealsohad
grassstripsbetween cropplots.Percentages ofE.I.higherthanc.2%(Table 1)weremainly
duetothepresenceofthesegrass strips.Onlyfarms K,LandEpossessed aboundaryplanted
withahedgerow. Spatial density ofE.I.ispurposively increased on farm E(Smeding&
Joenje, 1999)and farm L;thespatial arrangement ofE.I.ontheother6farms mainly reflects
landscape-scale features.
Extremetypesofvegetation management are:
- 'traditional management' involving threeor four morecutsperyearwith aflail mower
leavingtheshredded cuttings insitu;
- 'latemowingmanagement' involving oneortwo cutsperyear after June 21st with a fingerbarmowerwith hiabgrabfor removal ofcuttings.
Thegrass strips alongthecanalsarerequired fortransport on farms with a'latemowing
management'. E.I.areaistherefore relatedtomowingdate.InthisarticletheE.I.with
enlarged areaand latemowing isdefined as'improved E.I.1.Theimproved E.I.onfour farms
(A,T,L,andD)wascreated duringtheEAFS-prototyping researchprogram in 1992-1997
(Vereijken, 1997).Theimproved E.I.ontheexperimental farm Estarted in 1995
simultaneously withconversion oftheconventional dairy farm toanorganicmixed farm
(Smeding &Joenje, 1999).
58
Dominant plant speciesincanalbank swards are:couch(Elymus repens),perennial meadow
grasses (Festuca rubra,Poatrivialis,Loliumperenne,Agrostisstolonifera),commonreed
(Phragmitis australis)and fewperennialherbs:dandelion {Taraxacum officinale) and
stingingnettle(Urtica dioica).Canalsthat aretraditionally managed have alow,relatively
open,speciespoorvegetation (<10species/4m2),dominated byafew grass species.Late
mowingparticularly relatestoincreasedvegetationbiomassinJuneandJuly asexpressedby
vegetationheight (upto 1-3 m)andcover(upto90-100%).However, latemowingdoesnot
alwaysrelatetoincreasedhigherplant speciesdiversity fortworeasons:a)tallgrass species
maydominatethesward;b) swardsthathavebeentraditionallymanaged maybecut locally
togroundlevelandtherefore beinvadedbyruderals andannuals (increased speciesnumber
upto 15species/4m2),e.g. thistles(Cirsium arvense, Sonchusarvensis),annualweeds(e.g.
Sonchusasper,Polygonumaviculare)and annualsthat arerarelyperniciousweedsin
Flevoland (e.g. Myosotisarvensis, Veronicapersica, Cardaminehirsuta).
Highperennialplantdiversities found insomelocationsmaybecausedby various
interrelated factors (Kleijn, 1997);suchasreduced vegetationproductivity,removal ofthe
hay,nutrient buffering bythegrass strip,andlongorganicduration. Artificial species
introduction ishowever, also involved. IntheEAFS-project, around 90different native
perennial dicotswere artificially seededintothecanalbankstoobtainhigherplant diversity
and flower abundanceofplantswith limiteddispersal capacity (Vereijken, 1998).Although
few speciescould settlewell(e.g. Seneciojacobea, Crepis biennis,Heracleum sphondylium),
theintroduction clearly affected speciesdiversity:vegetation including siteswith>15
species/4m2wasconfined toprototype farms.
2.2.Samplingandmeasurements
2.2.1.Birds
Territorymapping ofskylarkwasdone four timesin 1998andthreetimesin 1999,inthe
beginningofMay (week 19),aroundtheendofMay(week22),aroundthemiddleofJune
(week25)and,onlyin 1998,aroundthebeginning ofJuly (week28),using themethod
described inVanDijk (1993).Arepresentativepart (80-100%)ofthe farm, excluding the
farm yard,wasselected. Farmswerevisited inthemorningbetween 8:30-12:00h.
Observationsweredonewhile slowlywalking alongtransport tracksandcanalbanks,within
afree observationrangeof200mtoboth sidesofthetransect.Birdobservationswereplotted
ona 1:5000field map,includingterritorialbehaviour(singing, fighting, mating)orother
nesting indications (nestvisits,feeding andpresence ofchicks).
Fieldmapswereinterpreted accordingtoVanDijk (1993):observationswerecollected on
individual bird speciesmaps.Separatesightingswithin specific merger distances were
attributed tothesameterritory,unlesstwoindividualswereseen simultaneously.
Breedingbirdsweregrouped accordingto food types andhabitat preferences:
1. Insecti-granivorous birdswithcropareapreference: skylark (Alauda arvensis);
2. Insecti-granivorous birdswithE.I.preference: linnet(Carduelis cannabina)and goldfinch
(Carduelis carduelis),both finch species(Fringillidae);
3. Specialist insectivorousbirdswithcombined cropareaandE.I.preference: blue-headed
wagtail (Motacillaflava),whitewagtail (Motacilla alba)andmeadowpipit(Anthus
pratensis)membersofthebird family Motacillidae;
4. SpecialistinsectivorousbirdswithE.I.affinity, defined as'marshbirds'(accordingto
Remmelzwaal &Voslamber, 1996):reedwarbler (Acrocephalusscirpaceus),reedbunting
(Emberizaschoeniclus) andbluethroat (Lusciniasvecica).
59
5. Insecti-granivorous birdsonthefarm, including groups 1.and2.mentioned aboveand
alsoafew observations ofquail(Coturnixcoturnix) whichisnot asongbird buthas
requirements similartothefirstgroup;
6. Specialist insectivorousbirdsonthefarm, including groups 3.and4.mentioned above;
7. Totalsongbirdsincluding insecti-granivorous birds and(specialist) insectivorousbirds;
8. Soillife-feeding birds:lapwing (Vanellus vanellus), oystercatcher(Haematopus
ostralegus)andblacktailed godwit (Limosa limosa).
Observations ofswallow (Hirundo rustica), housemartin(Delichon urbica),starling (Sturnus
vulgaris)andhousesparrow(Passerdomesticus)werenot included becausethese species
nestinfarmyards andstablesandmostly stayaroundthefarmyard orareaccidentally present
inthefieldsofadjacent farmland. Linnet,goldfinch andwhitewagtail alsodonotnestinthe
openfieldbut aremuchmoreresident inparticularpartsofthearablefields.Observationsof
soil life-feeding birdswereinterpreted withcautionbecausethemostcommon species,
lapwing,requiresobservations inApril(VanDijk, 1993).
2.2.2. Arthropods
Samplingwasdoneinwheatcropsandonadjacent canalbanks (E.I.)- Wheat (Triticum
aestivum) waschosenasarepresentative cropbecausethiscrop iscommon onorganic arable
farms inFlevoland and arthropod numbersincereals arelargercompared tonumbersinother
commoncrops likepotatoesandonions (Booij &Noorlander, 1992).
In 1998grounddwelling arthropods weresampledbysixpitfall trapsplaced inarowwith
intervalsof 10matdistancesof0m(E.I.)and30m(wheat).Weeklysamplesweretaken
during 8weeks,starting from 6thofJuneuntil 28th ofJuly 1998.Individualsweresortedto
taxaatorder-or family-level andplacedinto sixdifferent arthropod functional groups (for
further details seeSmeding etal, 2001a):
- Predaciousbeetlesincluding carnivorous Carabidae and large(>6mm) Staphylinidae;
- Lycosid spiderswhicharelargeandrepresent diurnal wandering spiders;
- Linyphiid spiderswhicharesmallandrepresent sheet-webspiders;
- Smallstaphylinidbeetleswhichrepresent animportant detritivorous functional group;
- Granivorousherbivores represented bygranivorous carabidbeetles;
- Folivorousherbivoresrepresentedbyweevils(Curculionidae) andhoppers (Cicadellidae).
Theobservations ofthe sixtraps andeight samplingdateswere accumulated givingonetotal
numberperfunctional groupperhabitat (croporE.I.)per farm.
In 1999vegetation dwelling arthropodswerecollected bymeansofavacuum sampler(ES
2100,Echo,LakeZurichU.S.A.) for 120sateach 1 m2sample.Nine samplesof 1 m2at
distancesof0m(E.I.) and30m(wheat)wereselected. Samplingwasdoneoncebetween
June7thandJuly 6th.Taxawereplaced intotrophic categories (for further detailssee Smeding
etal, 2001b):
-Detritivores;
-K-orsenescense-feeding herbivores (White, 1978);
-r-or flush-feeding herbivores (White, 1978),representedby aphids (Aphididae)
-Predators;
-Parasitoids,represented byParasitica(Hymenoptera).
Theobservations oftheninesuction sampleswereaccumulated, giving onetotalnumberper
functional groupperhabitat (croporE.I.)per farm.
60
2.2.3. Vegetation measurements intheE.I.
Vegetation studiesincluded thebanksofsmallcanals (width<4m)thatwere adjacent tothe
crops;investigationwasdonefrom MaytoAugust:latemownvegetationwasinvestigatedin
June andJulybefore thefirstcut.Early andorfrequently mownvegetation was investigated
before thefirstcut (May)orlater(untilAugust)when speciescomposition could sufficiently
beidentified. Investigationwasdoneoncein 1997-1999.Speciesnumberwereassumed tobe
moreorlessconstant overthetwoyears.Observations onvegetation height andcoverwere
influenced bysampling dateanddifferences betweenyears;howeverbyinvestigating many
plots including allcanalbanks (width<4m)onthefarm, therewassufficient representation
ofgeneralperformance, standing cropandoccurrence ofgapsinthe sward.
Theherblayerwas sampled inplotsof4m2areawith intervalsof50mbetweenplots.Plots
includedtheditchbankvegetation from thetoptothehelophytic zone;and vegetation
affected bysubmersionwas excluded.Parameters were:cover,maximumheight,plant
species anddominantplant species(totalling 80%ofthecover).Averageswerecalculated for
eachfarm. Thedatabase comprised 397plotswith30-50plotsper farm.
2.2.4. Farmmanagementandlayout
A 1:5000mapwasmadeofeach farm, depictingthedifferent cropsandthe ecological
infrastructure (E.I.)andonthesemapstheareaofthecropsandofsemi-naturalhabitatswere
measured.
Measurements offarm characteristicswererestrictedtoarepresentative farm areainwhich
thebirdterritories weremapped,whichwas 80-100%ofthetotal farm area.However, crop
rotation intensity (%gramineous crops,including leypasture andcereals)wascalculated for
thewholearablecrop areabecausethisfigureindicatedboththeinput ofcarbon aswellasa
specific habitat withinthebird mapping area.
The'E.I.area' iscalculated asthepercentageof semi-natural habitat oftherepresentative farm
area. ThespatialdensityoftheE.I.wasexpressedbythepercentage ofthe farm whichlay
within a 100mdistance oftheE.I. Incasethecanalbankvegetation was cutboth after
September 15th aswellasbefore May 15th,adistanceof70mwas considered.
Weed abundance inthecrop areawasmeasured inthefieldusing asimplified Tansley scale
(with 0.5=few individuals, 1 =rare,2=occasional,4=frequent, 8=abundant; 10=codominant);weed abundancewasestimated duringhalfofJuneineachcrop.Aweighted
averagevaluewascalculated for eachfarm,basedontheproportionsofthecropswithinthe
areawherethebirdterritoriesweremapped.
Dataonconversion toorganic,operations inthewheatcropin 1998,andthemowingof
canalsbanks andgrass stripswasobtainedbyusingaquestionnaire. Durationisdefined asthe
number ofyears sincethewholecropareaofthefarmwascertified accordingtotheEuropean
regulations for organic farming (Anonymous, 1991).Thetimingofmowing isrepresentedby
themonthofthefirstcut andthefrequency per year.
2.2.5. Landscape
Landscapeparameterswere sampled around 8farms in 1998,inanareaof200hawhich
included theinvestigated farm. Theareahad arectangular shapewith alength andwidthratio
congruent tothe farm andpositioned inthesameorientation asthefarm. Thefarm was
situated inthecentre.Insidetherectangletheareaofdifferent crops,semi-naturalhabitats,
roads,pavements andurban occupation weremeasured.Thesemi-natural aquatic,woody,tall
herb andgrassyhabitatsweredefined as'natural'.
61
2.3.Statisticalanalyses
Allmeasurementsweretested for normality.Arthropod numberswereIn-transformed. All
subsequent analyseswereconducted usingStatistical Analysis System (SAS Institute,Cary,
North Carolina).Therelativeimportance ofarthropods,croparea andE.I.characteristicson
birdterritorydensityweredetermined usingmultivariate REGMAXRregression.
Eight explored response variableswere:skylarks,wagtails/pipit, finches, marshbirds,
insectivores,insecti-granivores, totalsongbirds andsoil life-feeding birds.
Therewerefour separate analysesconcerning arthropods andfarm environmental factors in
twodifferent years andoneadditional analysisconcerning thelandscape factors. These
analysesincludethefollowing predictorvariables:
1. withregardtoground dwelling arthropods (1998),twelvevariables incrop andE.I.:
predaciousbeetles,lycosid spiders,linyphiid spiders,small staphylinids, granivorous
carabids and folivorous insects;
2. withregardtovegetation dwelling arthropods (1999),tenvariables incrop areaandE.I.:
r-herbivores,K-herbivores, detritivores,predatorsandparasitoids;
3. withregardtofarm andE.I.characteristics in 1998,tenvariables:organic duration,
intensity, spatialdensityofE.I.,areaofE.I.,mowingdate,mowingfrequency, maximum
height, cover,plant speciesnumber anddominant plant species number;
4. withregardtofarm andE.I.characteristicsofsevenfarms inOostelijk Flevolandin 1999,
thesametenvariables asin 1998wereused andalsoweed abundance:the sameanalysis
wasperformed includingtwomore farms inZuidelijk Flevoland becausethese farms were
also involved instudiesof 1998butnotinarthropod studiesof 1999thatwereconfined to
Oostelijk Flevoland;
5. withregard tolandscape structureofeight farms in 1998,fivevariables:ageofthepolder,
proportion ofsemi-naturalhabitats,proportions ofvegetable crops,lifted cropsand
gramineous crops.
Inthemultipleregressionsallpredictorvariableswereincluded inboth linearand quadratic
form tofind both linearandquadraticrelationsbetweenresponse andpredictor variables.
Multipleregression modelsincluded maximally4variables(Maxr; STOP=4).Foreach
responsevariablethebestmodelwasselected according tothe following criteria:
- theR-square ofthemodel waslargerthan50%;
- thesignificance leveloftheeffects ofallindividual variables andthemodel shouldbe
smallerthan0.05;
- themodelwiththehighest probability wasconsidered asthebestmodel.Butifthemodel
withthehighestprobability, ascompared tothebestmodelwith onevariable less,hadthe
sameprobabilityclassand addedlessthan5%totheR-square,thanthemodelwith fewer
variableswas considered asbetter.
62
3. Results
3.1. Observedbirdspeciesandterritorydensities
In 1998within 422ha study area, 169territories ofinsectivorous and insecti-granivorous
birdswerecounted andin 1999within467hastudy area, 133territories were counted.
Observations inbothyearsincluded 10species(Table2).Additional observationsofsoillifefeeding birdsyielded 39territories inboth years,including 3species (Table2).
Mostterritories (c.39%)concerned skylark (Alauda arvensisL.),thathadterritory densities
ranging from 0.06-0.24perhawith averagedensitiesof0.15and 0.12territoryperhain 1998
and 1999respectively. Othernumerous specieswerelinnet (Cardueliscannabina L.) (c. 18%
ofobservations) andmeadowpipet (Anthuspratensis L.)(c. 13% ofobservations).Soil lifefeeding birdsweremainly (c.90%)lapwing (Vanellus vanellus L.).
3.2. Birdfunctional groupsinrelationtoarthropodfunctionalgroups
Skylarkterritory densitywas found tobepositively relatedtoarthropod functional groups
(Table3)inthe E.I.,particularly tothediurnal predacious groups:lycosid spiders in 1998
(Table4)andvegetation dwellingpredatorsin 1999,butalsotoherbivoresin 1999(Table5).
Withregard to arthropods inthecrop area,r-herbivores were animportant predictor in 1999
(Table 5).Multiple regression selected asbest 1-variablemodel:
ALAU=0.0003+0.0029(rHERB)2(R2=0.66;PO.034).
Table2
Observations of birdterritories: the territory numbers of differentspeciesperform, thesize of thestudy area,
and thedensities of thefunctional groups. Theassemblages areexplained in themethod section.
1998
Farm
Birds
Skylark
Linnet
Goldfinch
Quail
Blue-headed wagtail
White wagtail
Meadow pipit
Reed warbler
Bluethroat
Reed bunting
Lapwing
Oystercatcher
Black-tailed godwit
Bird mapping area (ha)
1999
A
N
T
F
R
L
E
D
A
N
T
F
K
Z
R
L
E
4
3
0
1
1
2
0
1
1
3
0
0
0
15
4
0
4
2
2
1
0
0
3
7
0
0
9
3
1
2
2
1
2
0
0
1
5
0
0
9
4
0
0
1
2
5
0
0
0
4
0
0
9
2
0
2
1
1
4
0
0
0
5
0
0
4
3
0
1
2
1
7
0
0
0
4
0
0
4
5
1
2
1
3
1
0
0
0
2
3
1
8
5
1
0
2
1
9
0
0
0
7
1
0
2
2
0
0
1
2
0
4
2
0
1
0
0
12
5
0
0
1
3
0
1
0
0
8
0
0
8
2
1
0
1
2
1
2
0
0
3
0
0
5
2
0
1
2
1
2
0
0
0
3
0
0
7
6
0
1
0
1
0
0
1
1
5
0
0
5
1
0
0
0
1
0
0
0
0
3
0
0
7
2
0
1
1
2
0
0
0
0
8
0
0
5
5
0
1
1
1
6
0
0
0
4
0
0
4
4
0
1
1
2
0
0
0
0
2
2
0
39
93
37
47
57
34
68
47
39
93
37
47
45
47
57
34
68
Skylarks n/10 ha
Finches n/10 ha
Motacillidae n/10 ha
Marsh birds n/10 ha
Insecti-granivores n/10 ha
Insectivores n/10 ha
Total songbirds n/10 ha
1.0
0.8
0.8
1.3
2.0
2.0
4.1
1.6
0.4
0.5
0.3
2.5
0.9
3.3
2.4
1.1
1.3
0.3
4.0
1.6
5.6
1.9
0.9
1.7
0.0
2.8
1.7
4.5
1.6
0.3
1.0
0.0
2.3
1.0
3.3
1.2
0.9
2.9
0.0
2.3
2.9
5.3
0.6
0.9
0.7
0.0
1.8
0.7
2.5
1.7
1.3
2.6
0.0
3.0
2.6
5.6
0.5
0.5
0.8
1.5
1.0
2.3
3.3
1.3
0.5
0.4
0.1
1.8
0.5
2.4
2.1
0.8
1.1
0.5
2.9
1.6
4.5
1.1
0.4
1.1
0.0
1.7
1.1
2.8
1.6
1.3
0.2
0.4
3.1
0.7
3.8
1.1
0.2
0.2
0.0
1.3
0.2
1.5
1.2
0.3
0.5
0.0
1.7
0.5
2.3
1.5
1.5
2.3
0.0
3.2
2.3
5.6
0.6
0.6
0.4
0.0
1.3
0.4
1.8
Soil life-feeders total n/10 ha
0.0
0.8
1.3
0.9
0.9
1.2
0.9
1.7
0.3
0.9
0.8
0.6
1.1
0.6
1.4
1.2
0.6
63
Table3
Observations of arthropodsperform: datafrom 1998representing total numbers ofground dwelling arthropod
functional groups captured in 6pitfall traps inweekly trappings over aeight weekperiod in thewheatcrop (30
mfrom thefield margin) as wellas inthe ecological infrastructure; datafrom 1999representing thetotal
number/9 m'perfarm of vegetation dwelling arthropods inthe wheatcrop (30mfrom the field margin) andin
theecological infrastructure, captured by vacuumsampling.
Crop area 1998
Arthropod functional groups (n/trap)
Ground dwelling 1998
Predacious beetles inwheat 30m
Lycosidae inwheat 30 m
Linyphiidae inwheat 30m
Staphylinidae <6mm inwheat 30m
Carabidae granivorous inwheat 30m
Folivorous insects inwheat 30m
Crop area 1999
Arthropod functional groups (n/9m2)
Vegetation dwelling 1999
r-Herbivores total
K-Herbivores total
Detritivores total
Predator total
Parasitoids total
EI 1998
Arthropod functional groups (n/trap)
Ground dwelling 1998
Predacious beetles inwheat 30m
Lycosidae inwheat 30 m
Linyphiidae inwheat 30 m
Staphylinidae <6mm inwheat 30m
Carabidae granivorous inwheat 30m
Folivorous insects inwheat 30m
EI 1999
Arthropod functional groups (n/9m2)
Vegetation dwelling 1999
r-Herbivores total
K-Herbivores total
Detritivores total
Predator total
Parasitoids total
abbrev.
COL
LYC
LIN
STSM
CARH
FOLI
Farms:
A
952
53
3061
1308
5
4
T
N
F
1064 1333 3765
146
57
38
3311 2979 2622
329 893 425
83
7
4
3
7
21
Farms:
A
N
rHERB
KHERB
DETR
PRED
PAR
COL
LYC
LIN
STSM
CARH
FOLI
*
*
*
*
*
Farms:
A
1365
87
2508
739
52
104
*
*
*
*
*
*
*
*
*
*
F
219
12
24
31
60
N
T
F
1319 1205 2808
535 208 302
2577 880 4235
703 444 334
149
83
79
275 150
33
Farms:
A
N
rHERB
KHERB
DETR
PRED
PAR
T
2379
20
19
33
94
*
*
*
*
*
T
488
471
395
254
88
F
11
71
67
104
14
K
Z
*
*
*
*
*
*
*
*
*
*
*
*
K
836
28
45
85
68
z
K
Z
*
*
*
*
*
*
*
*
*
*
*
*
K
45
24
43
158
27
Z
106
341
79
158
95
E
D
R
L
1011 1035 2889 1731
35
8
18
83
2515 2055 1687 1944
640 772 205 541
19 504
15
3
8
5
6
13
R
413
36
66
93
156
743
15
23
33
66
E
189
58
63
221
79
D
*
*
*
*
*
E
D
R
L
832 1706 2603 926
64
46 168 226
1191 1607 1930 2554
365 217 411 709
253 291 279
66
38
61
35 100
R
127
831
45
121
49
Finches(mainly linnet) territorydensitywasfound tobepositively related tovegetation
dwellingpredators inboth cropareaandE.I. andwasfound tobenegatively related to
herbivorous groups intheE.I.(granivorous beetles andK-herbivores in 1998and 1999
respectively) and alsonegatively relatedto linyphiid spiders inthecroparea in 1998and
parasitoids inE.I.in 1999(Tables4and5).
Motacillidae (wagtails/pipit) territorydensitywas found tobepositively related to lycosid
spiders intheE.I. in 1998(Table4) andtodetritivores intheE.I.in 1999(Table 5).In 1998
64
L
377
42
48
39
152
L
59
509
440
336
47
E
35
145
98
96
35
D
*
*
*
*
*
Motacillidaewerenegatively related tolinyphiid spidersandcurvilinearly to granivorous
carabidsinthecroparea(Table4).
Marshbirdterritory densitywasbestpredictedby small staphylinidbeetlesinthecropareain
1998(Table4)andbyr-herbivores andparasitoids intheE.I.in 1999(Table5).
Insecti-granivorous birdsterritory density (including skylark, linnet,goldfinch andquail)was
bestpredicted byvegetation dwellingpredatorsintheE.I. (Table 5).Nomodelwithregardto
grounddwelling arthropod observations,wasobtained in 1998(Table4).
Insectivorousbirdsterritory density(includingblue-headed andwhitewagtail,meadowpipit,
reedwarbler, reedbunting andbluethroat)wasfound tobecurvilinearly related to detritivores
intheE.I.andtor-herbivores intheE.I. (Table5).Themostimportantpredictorwas
vegetation dwelling detritivores intheE.I.:Multipleregression selected asbest 1-variable
model:INSECT =0.0066(DETREI)2 - 0.0054 (R2=0.71;PO.017).Nomodel forinsectivorousbirdsinrelation togrounddwelling arthropod observationswas found (Table4).
Table 4
Multiple regression models (P<0.05) with ground dwelling arthropods as predictor variables based on bird and
arthropod observations on eight farms in 1998; Birds (territory/ha): Alau = skylark, Mota = Motacillidae, Fin =
Finches, Marsh = Marsh birds, Insect = Specialist insectivorous birds; Insgran= Insecti-granivorous birds; Avis
= total songbirds; Soilf = soil life-feeding birds; Ground dwelling arthropods; COL =predacious beetles; L YC
= lycosid spiders; LIN = Linyphiid spiders; STSM = small staphylinid beetles; CARH = granivorous carabids;
additional symbols: 'ca' =crop area; 'ei' = ecological
infrastructure.
Birds
Alau
Fin
Mota
Marsh
Insgran
Insect
Avis
Soilf
Model
-0.063'ln(LYCca)- 0.005«ln(CARHca)2+0.010*ln(LYCei)2-0.004*ln(LINei)2 +0.437
-0.11*ln(LINca)-0.04*ln(CARHei)2 +1.0612
-0.42*ln(LINca) +O.U'lnfCARHca) -0.025*ln(CARHca)2 +0.039*ln(LYCei) + 3.071
-0.96*ln(STSMca) +0.08*ln(STSMca)2+ 2.839
No model
No model
Nomodel
-0.36'ln(LINca) -0.03*ln(CARHca) -0.15*ln(COLei)+0.1*ln(LYCei) + 3.53
R"
96
72
99
74
Pr>F
0.0162
0.0401
0.0011
0.0327
94
0.0390
Table 5
Multiple regression models (P<0.05) with vegetation dwelling arthropods as predictor variables based on bird
and arthropod observations on eight farms in 1999; Birds (territory/ha): Alau = skylark, Mota = Motacillidae,
Fin = Finches, Marsh = Marsh birds, Insect = Specialist insectivorous birds; Insgran=
Insecti-granivorous
birds; Avis = total songbirds; Soilf =soil life-feeding birds; Vegetation dwelling arthropods: rHERB = rherbivores; KHERB= K-herbivores; PRED =predators; DETR = detritivores; PAR =parasitoids;
additional
symbols: 'ca' = crop area; 'ei' = ecological
infrastructure.
Birds
Alau
Fin
Mota
Marsh
Insgran
Insect
Avis
Soilf
Model
0.063•ln(rHERBca)+0.0014*ln(KHERBei)2+0.038*ln(PREDei) -0.077*ln(PARei)-0.244
0.034*ln(PREDca) -0.014*ln(KHERBei)+0.139*ln(PREDei)-0.004*ln(PARei)2-0.632
0.006*ln(DETRei)2 -0.059
-0.044*ln(PARei)+0.003*ln(rHERBei)2 +0.076
0.147*ln(PREDei)-0.527
-0.671*ln(DETRei)+0.075*ln(DETRei)2 -0.029*ln(rHERBei)2+1.703
0.366*ln(PREDei) -0.017*ln(PARei)2- 1.284
0.0068*ln(PARca)2 -0.154*ln(KHERBei)+0.015*ln(KHERBei)2+0.332
65
R*
100
100
62
99
62
97
94
99
Pr>F
0.0068
0.0018
0.0346
0.0002
0.0354
0.0074
0.0035
0.0011
Total songbird territory densitywasbestpredicted byvegetation dwelling arthropods inthe
E.I.(Table 5)andwaspositivelyrelatedtopredatorsandcurvilinearly toparasitoids.Total
songbird territorydensitywasalsopredicted fairly wellbyaone-variablemodel:
AVIS=0.027(PREDEI) - 0.38 (R2=0.71;PO.035).Nomodel for totalbird densityin
relationtoground dwelling arthropod observations was found (Table4).
Territory densityofsoillife-feeding birdshadground dwelling arthropods inboth croparea
andE.I. aspredictorvariables andwasfound tobepositively related tolycosid spidersinthe
E.I.andnegatively relatedtolinyphiid spidersgranivorous carabids inthecrop areaand
predaciousbeetlesintheE.I.(Table4).Withregardtovegetationdwellingarthropods,soil
life-feeding birdterritory densitycouldbestbepredictedbyparasitoid abundance inthecrop
area(which clearly isanassociationbecausethesebirdsdefinitly donot feed onthisgroup)
andK-herbivores intheE.I. (Table5).
3.3.Birdfunctional groupsandrelations tofarm andE.I. characteristics
Skylarkterritory densitywasfound tobepositivelyrelated tolatemowing andnegatively
relatedtohighvegetation coveroftheE.I.inboth 1998and 1999(Tables 6and 7),and
positivelytoorganicduration ofthefarm in 1999.IfthetwoZuidFlevoland farms were
includedinthestudyarea,then Skylarkterritory densitywasalsopredictedbythespatial
densityofE.I. (Table8).
Finches (mainly linnet)territory densitywasfound tobepositively related to spatial density
ofE.I.andplant speciesrichnessofE.I.vegetation in 1998(Table6)andorganicdurationand
areaofE.I.in 1999(Table7);in 1999anegativerelationwas found topercentageof
gramineous crops inthecroprotation (Table7).
Motacillidae (wagtails/pipet)territory densityin 1998and 1999,was found tobepositively
related tospatial E.I. features (E.I.areain 1998andE.I.density in 1999)and negatively
related topercentage ofgramineous crops (Tables 6and7).In 1998itwasnegatively related
tomowing frequency andin 1999alsonegatively toheight ofE.I.vegetation but positivelyto
number ofdominant plant species.Ifthetwofarms inZuid Flevoland were included inthe
study areathanwagtails/pippit werealso found toberelatedpositively toweed abundance
whereas spatialdensityofE.I.wasnolongerincluded inthemodel (Tables 7and8).
Marshbirdterritorydensitywasfound tobe exponentiallyrelated toheight oftheE.I.
vegetation in 1998and 1999(Tables 6and 7)andcurvilinearlytoorganicduration in1999
(Table 7)andwas found tobenegatively related toareaandcurvilinearlytolatemowingof
theE.I.in 1998(Table6).
Insecti-granivorousbirdterritory density(includingskylark, finches, goldfinch andquail)was
found tobepositively related tolatemowing ofE.I.in 1998and 1999(Tables 6and 7)and
organicduration in 1999(Table7)andwasfound tobenegatively related tofrequent mowing
andopenvegetation in 1998(Table6)andalsotoE.I.dominantplant speciesnumber in 1999
(Table 7).Ifthetwofarms inZuidFlevoland wereincluded inthe studyareathaninsectigranivorousbirdterritory densitywasalsopredicted byE.I.densityandwas found tobe
negatively related tomowing frequency andE.I.plant speciesnumber (Table8).
Insectivorousbird territory density (includingblue-headed andwhitewagtail,meadow pipit,
reedwarbler, reedbunting andbluethroat) wasfound tobepositively related toE.I.dominant
plant speciesnumber andnegatively topercentage gramineous cropsin 1998and 1999
66
(Tables6and7)andnegativelytoE.I.spatialdensityin 1999.IfthetwoZuidFlevoland farms
wereincludedthentheselectedmodelincludedweedabundanceasapredictorforinsectivorous
birdterritorydensity,whereasE.I.spatialdensitywasnotincluded (Table8).
Totalsongbirdterritorydensitywasfound tobepositivelyrelatedtoplantspeciesnumberofE.I.
vegetationin 1998and 1999(Tables6and7)andlatemowingandmowingfrequency in1999
(Table7),andnegativelytopercentagegramineouscrops,mowingfrequency andcoverofE.I.
vegetationin 1998(Table6).IfthetwoZuidFlevoland farmswereincludedthentheselected
modelincludedorganicdurationasapredictorfortotalbirdterritorydensity,whereasE.I.plant
speciesnumberwasnotselected(Tables7and8).
Soillife-feeding birdterritorydensitywasfound tobepositivelyrelatedtolatemowingand
curvilinearlytoheightofE.I.vegetationin 1998(Table6)andpositivelyrelatedtoorganic
durationandnegativelyrelatedtopercentagegramineouscropsandspatialdensityofE.I.in1999
(Table7).IfthetwoZuidFlevolandfarmswereincludedthennosignificant modelcouldbe
found (Table8).
Table 6
Multiple regression models (P<0.05) with farm and E.I. characteristics as predictor variables based on bird
observations (response variables) on eight farms in 1998. The keys are in Table 5 (birds) and Table I (farm and
E.I. characteristics).
Birds
Alau
Fin
Mota
Marsh
Insgran
Insect
Avis
Soilf
Model
0.0033*(MOW)2-0.00006*(EICOV)2+0.479
0.0015«(EI100)-0.0126*(AREA) +0.0106*(EISPN) -0.094
-0.0002*(iNT)2-0.6678*(AREA) +0.1478*(AREA)2-0.1219*(MOWFRQ)+ 1.214
-0.0033*(AREA)2+0.185*(MOW)-0.0146*(MOW)2+0.0446*(EIHGT)2-0.584
0.0036*(MOW)2-0.0174*(MOWFRQ)-0.00008*(EICOV)2+ 0.841
-0.0037*(INT) +0.126*(EIDOM)- 0.1008
-0.0029*(INT) -0.159*(MOWFRQ)2-0.00007*(EICOV)2+0.026*(EISPN) + 1.23
0.0038*(MOW)2+0.309*(EIHGT) -0.187*(EIHGT)2- 0.135
78
99
99
97
95
83
98
97
Pr>F
0.0231
0.0003
0.0029
0.0163
0.0048
0.0117
0.0045
0.0011
Table 7
Multiple regression models (P<0.05) with farm and E.I. characteristics as predictor variables based on bird
observations (response variables) on seven farms in Oostelijk Flevoland in 1999. The keys are in Table 5 (birds)
and Table 1 (farm and E.I. characteristics).
Birds
Alau
Fin
Mota
Marsh
Insgran
Insect
Avis
Soilf
Model
0.0001*(DUR)2+0.0035*(MOW)2+0.0059*(MOWFRQ)2-0.0059*(EICOV)+0.483
0.0088*(DUR) -0.0020*(INT)+0.0063*(AREA)2 +0.0308
-0.0068*(INT)+0.00003*(EI100)2-0.044*(EIHGT)2 +0.057(EIDOM)2-0.37
-0.0077*(DUR) +0.0006*(DUR)2+0.021*(EIHGT)2 +0.0014
0.014*(DUR) +0.036*(MOW)-0.018*(EIDOM)2+0.053
-0.00007*(INT)2-0.00005*(EI100)2 +0.198*(EIDOM)+0.666
0.0148*(MOW)2+0.253*(MOWFRQ)-0.334*(EIHGT) +0.057*(EISPN)2- 1.015
0.0002*(DUR)2 -0.002*(INT) - 0.00003*(EI100)2 +0.023
100
99
99
98
98
95
100
94
Pr>F
0.0007
0.0005
0.0119
0.0056
0.0049
0.0186
0.0009
0.0251
Table 8
Multiple regression models (P<0.05) with farm and E.I. characteristics as predictor variables based on bird
observations (response variables) on nine farms in Oostelijk and Zuidelijk Flevoland in 1999. The keys are in
Table 5 (birds) and Table 1 (farm and E.I. characteristics).
Birds
Alau
Fin
Mota
Marsh
Insgran
Insect
Avis
Soilf
Model
0.0033*(DUR)2+0.000012*(EI100)2+0.0034*(MOW)2-0.00006*(EICOV)2+0.347
0.0084*(DUR) -0.000009*(EI100)2+0.0227*(MOW)-0.0751*(EIHGT)- 0.109
-0.00002*(INT)2+0.0559*(WABUN) +0.3127*(MOW)-0.0201»(MOW)2+1.122
-0.216*(MOW)+0.0138*(MOW)2-0.144*(EISPN) +0.0101*(EISPN)2+ 1.243
0.0268*(DUR) +0.0036*(EI100)-0.129*(MOWFRQ)2-0.0625*(EISPN) +0.597
-0.0024*(INT)2+0.0404*(WABUN)+0.0026*(EISPN)2+0.128
0.0158*(DUR)+0.112*(MOW) -0.0994»(EIHGT)2 -0.371
No model
67
R2
98
99
93
98
88
95
89
Pr>F
0.0015
0.0006
0.0121
0.0008
0.0418
0.0012
0.0081
3.4.Birdfunctional groupsandrelations tolandscapecharacteristics in1998
Table9ispresentingthesignificant best multipleregression models for bird functional
groups,usinglandscape characteristics aspredictorvariables;semi-natural habitats included
canals,canalbanks,roadverges,tallherbs,shrubs andwoodlots.
Table9
Multiple regression models (P<0.05) withfarm and E.I. characteristics aspredictor variables based onbird
observations (response variables) on eightfarms in 1998.Keys in Table5 (birds) and Table 1 (landscape
characteristics).
Birds
Alau
Fin
Mota
Marsh
Insgran
Insect
Avis
Soilf
Model
0.048*(LSINT)- 0.00069(LSINT)Z-0.00011*(LSVEG)2- 0.557
0.000018»(LSAGE)2-0.031«(LSNAT)+0.0037*(LSINT)- 0.003*(LSVEG) + 0.154
-0.0067*(LSINT)
-0.024*(LSVEG)+0.0005*(LSVEG)2 +0.268
0.004*(LSAGE) +0.068*(LSINT) -0.001*(LSINT)a-0.007»(LSVEG)- 0.866
-0.28*(LSNAT) +0.021*(LSNAT)2-0.0001*(LSVEG)2 + 1.065
-0.057*(LSNAT) + 0.717
0.00005*(LSAGE) +0.00005*(LSVEG)2 +0.049
R"
94
97
51
83
96
97
58
88
Pr>F
0.006
0.012
0.045
0.011
0.021
0.001
0.028
0.005
Skylarkterritorieswerecurvilinearlyrelated toalandscapewithmanygramineous crops,and
negatively toalandscapewith ahighproportion ofvegetable crops.Finches (mainly linnet)
territory densitywasfound tobepositively relatedtotheageofthepolder andtothe
proportion ofgramineous crops,andnegatively related totheproportions of semi-natural
habitat andvegetablecrops.
Wagtails/pipetterritory densitywaspredicted byamarginally significant modelwhich
included anegativerelationtotheproportion ofgramineous cropsinthelandscape.Marsh
birdshad acurvilinearrelationtoahighproportion ofvegetable production.
Insecti-granivorous birdterritory density (including skylark, linnet,goldfinch andquail)was
found tobepositivelyrelated totheageofthepolder,negatively totheproportionof
vegetable crops andcurvilinearly togramineous crops.Insectivorousbird territory density
(includingblue-headed andwhitewagtail,meadowpipit,reedwarbler, reedbuntingand
bluethroat)wascurvilinearly related toahighproportionofsemi-natural habitat inthe
landscape andnegatively totheproportion ofvegetable crops.Total songbird territorydensity
wasbestpredictedbytheproportionoflandscapewith semi-natural habitat andwas found to
benegativelyrelated tothisvariable. Soillife-feeding bird territory densitywasfound tobe
positively related tothe ageofthepolder andtheproportion ofvegetable crops.
4. Discussion
4.1. Observations incomparison with hypotheses
Observations ofwagtails/pipet showedmost accordancewithhypotheses becausetheterritory
densityofthisgroup (insectivores withcombined cropandE.I.affinity) wasindeed relatedto
boththecrop areaandE.I.characteristics andmorepositively andmoreclearlyrelatedto
vegetation dwelling arthropods (including abundantflyingspecies)thantoground dwelling
arthropods.However ingeneral terms,similarobservationsweredonewithregard totheother
threegroups ofskylarks,finchesandmarshbirds.Thismeansthatfieldobservations didnot
provide indications for the expected E.I.preference offinches andmarshbirds andcroparea
68
preference ofskylark.Alsotheexpected associationbetween insecti-granivorous birdsand
ground dwelling arthropod abundancewasnot observed.
Withregardtocropareacharacteristicstherewas,according tothehypotheses,ageneral
positive relationtoorganic farming duration inthe 1999observations. Ourhypothesiswas
thatboth organic duration aswellasextensive croprotationwould enhancedetrital subweb
prey forbirds.However anegativerelation toextensivecroprotationwas found withregard
toseveralbird functional groups,andparticularly totheinsectivorous groups.
Withregardto ecological infrastructure variables,observations werelargelyin accordance
with ourhypotheses,because selectedmodels often includedpositiverelationsto
characteristics ofimproved E.I.,particularly latemowing andplant ordominantplant species
number.However somemodelshad seemingly inconsistent combinations ofcharacteristicsas
for example,earlymowingwithhigh vegetation.
Thesegeneral tendencies,whichhavebeendiscussed, canbeviewedinTable 10,which
showstheoccurrence ofthedifferent (typesof) variablesinall selected models.Thegeneral
tendencies arealsowell summarized inthebestmodels for total songbird territorydensity.
Thesemodels included positiverelationstovegetation dwellingpredators intheE.I.,plant
speciesnumber intheE.I., andorganicduration (in 1999)and anegative relationto
proportion ofgramineous crops (in 1998).
4.2.Crop area effects
4.2.1.Foodresources inthecrop area
Preference ofbirds for arthropods from theE.I.maysuggest thatbirdswereattracted away
fromfields withpoor food resources (O'Connor &Schrub, 1986).Preference ofskylarksand
blue-headedwagtails for field marginsonconventional farms was found byDe Snoo(1995)
intheHaarlemmermeerpolderandbyRemmelzwaal &Voslamber (1996) in 50hacropplots
inZuidelijk Flevoland.However, mean skylark territory densities onstudied organic farms in
1998(0.15/ha)and 1999(0.12/ha)werequitehighwhen compared tomeansin Zuidelijk
Flevoland andthe Groningen claydistrict: 0.09/haand0.11/ha,respectively (Remmelzwaal&
Voslamber, 1996).Densitiesofaround 0.2territories/hafound onfarms withhigh skylark
abundance,correspond todensitiesofgood skylarkhabitatsinvolved instudies ofPoulsenet
al.(1998) andWakeham-Dawsonetal.(1998)inGreat-Britain. Thismightbeanindication
that thestudiedorganic arable crop areascontributed tobird abundance.
4.2.2. Foodresources relatedtodetritivoreandherbivoresubsystems
Negativerelationstoextensive croprotation ofinsectivorous andinsecti-granivorous birds
wereopposit tothehypothesis.Apparently distributions ofbirds andcarabid beetlesand
linyphid spiders (involving >80%ofgrounddwellinginvertebrate numbers) didnotmatch.
Explanations may involve food aswellasotherenvironmental factors, howeverinthisarticle
weprimarily exploreexplanations concerning food resources.Apossible explanation might
bethattheincreased detrital subweb,related toincreased carbon supply,depressesthe
herbivore subweb (Wiseetal, 1999)whileherbivores arepreferred preyitems in 'chick-food'
(Hald&Reddersen, 1990;Moreby&Sotherton, 1997).Thisexplanation willbe explored
below.
69
Table10
An overview of the variables that were selected by significant multiple regression models based on bird territory density
(response variable) withfarm and E.I.characteristics aspredictor variables aswell as arthropod functional groups as
predictor variables. Key: Onthe horizontal axis birds: alau =skylark, mota =Motacillidae, fin - finches, marsh = marsh
birds, insect =specialist insectivorous birds; insgran- insecti-granivorous birds; avis =total songbirds; soilf=soil lifefeeding birds; Onthevertical axis, characteristics atthefarm and at theE.I. habitat level (key see Table I);down atthe left
side: ground dwelling arthropods: col=predacious beetles; lye =lycosid spiders, lin =linyphiid spiders; sism = small
staphylinid beetles; carh - granivorous carabids;foli=folivorous insects; down attheright side: vegetation dwelling
arthropods: Kherb—K-herbivores; detr =detritivores; pred= predators; par =parasitoids; rherb =r-herbivores; additional
symbols: 'ca' =crop area; 'ei'=ecological infrastructure.
1998
1999
Factor
Factor
3
s
o
B
dur
int
eilOO
area
mow
mowfrq
eihgt
eicov
eidom
eispn
colca
lycea
stsmca
linca
carhca
folica
colei
lycei
stsmei
linei
carhei
foliei
JS
c
IS
CA
s
X
X
4>
(A
a
ed
60
CA
a
X
X
X
X
'>
to
X
X
X
X
CA
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
c**
3
'o
CA
dur
int
wabun
eilOO
area
X mow
mowfrq
X eihgt
eicov
eidom
eispn
Kherbca
detrca
predca
X parca
X rherbca
X Kherbei
X detrei
predei
parei
rherbei
3
o
6
X
X
.s
X
X
CA
o
6
.9
CA
l-H
CA
C*H
'o
00
CA
CA
aX
X
X
X
X
X
X
X
3
X
X
X
X
X
X
X
X
X
X
X
X
X
X
—
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Theobservation that Skylarkterritory densityrelatedtor-herbivore (i.e.Aphididae)
abundance suggested thatthisbirdisassociated withanincreased herbivore subwebin
intensivecroprotation. However aphids areprobablynotimportant food item for skylarks
(e.g.Cramp, 1988;Poulsenetai, 1998)andmaytherefore indicateother(food resource)
factors.
Probably cropsinintensive organic farms aregenerallymorevulnerable topest outbreaks
thancropsinextensive organic farms duetocropphysiology (e.g. Phelan, 1997)aswellasa
lowerpredation pressure from detrital subweb-based polyphagouspredators.Thistypeofcrop
vulnerability isdemonstrated intheconventional plotsofvariouscomparative studies
includingvariouscropspecies (Kromp&Meindl, 1997).Timeseriesofarthropod numbersin
cropedgesofconventional crops(Remmelzwaal &Voslamber, 1999)withregardtovarious
cropspecies,showsimilar exponential increasesofarthropod numberswhich aretemporarily
higher than arthropod densitiesingrassmargins.Hald&Reddersen (1990)also found higher
arthropod densitiesinconventional cerealfieldsthan inorganicfieldsifthe exponentially
70
developing aphidsweretakeninto account.Theynotethat aphids aresupplementary preybut
thattheunpredictability oftheirdensitieslimitthecarrying capacityofconventional crops.
Onorganic farms inFlevoland spatialvariation ofindividual crop speciesmay compensate
for theshort time intervalsof crop-specific herbivore increases.Accordingly, spatial analysis
ofskylark territories (Nanetal, inprep.) showed anaffinity ofskylarksfor within-field crop
borders,whichmay facilitate foraging indifferent crops andcrop edges(Wilsonetal, 1997).
Theeffect ofpredationbypolyphaguouspredatorsmightbestronger onnumbers oflargesized invertebrateherbivores (K-strategists) thanonnumbersof small-sized r-strategists,
becauseK-strategist populations maybevulnerable duethescarcityofhostplants,both
weedy andundersown. Poornutritive quality ofadietcomprised ofmainlyr-herbivores {i.e.
aphids)may alsobeinvolved (Toft, 1996).Herbivorouspreyresources onorganic arable
farms inFlevolandmaytherefore includeonly asmallproportion of favourite items (sawfly
and lepidopteran larvae).However, inthiscaser-herbivores mayberelevant asfood resource
for insectivorousbirds.
Incropsorcroprotationswhere epigeicpredators exploitdetritivores and subsequently inhibit
herbivores,birdshaveto feed onthesepredators.However, food web structures inthese
habitatsrepresent apoorresource for chick food. Observations ofPoulsenetal.(1998)may
becoherent withourtheory: skylark chick diet andsurvival wascompared inthreedistinct
crophabitats(four yearold set-aside,grasssilage andspringbarley):nestlings in set-aside
received many small loadingsof small soft-bodied (i.e.herbivorousbutnoaphids) organisms
whichwereabundant inthatcrophabitat;nestlingsinbothothercropsreceived larger loads
includinghard-bodied organisms,particularly carabidbeetles.Inspringbarley arthropod
abundance waslowest andnestling dietincluded ahighproportion of spidersthatperhaps,
compensated for thelackoflargeritems;theobserved chickmortality inspringbarleywas
probably causedby starvation.
Examination ofarthropod communitiesprovided preliminary evidence for theseideas:
detailed analysisofgrounddwelling arthropod communities in 1998(Smeding etal, 2001a)
indicated thatwheatcrops inintensively managed farms, ascompared toextensive farms,had
lownumbersofepigeicpredators (andhighnumbers offungivorous small staphylinids)
whereaswheat cropsof farms with lessintensive (i.e.vegetable)production couldbe
associatedwithanabundanceofcarabidbeetles,granivorouscarabidbeetlesandlycosid
spiders.Detailed analysis ofthevegetation dwelling arthropod community onarablefarms in
Flevoland in 1999(Smeding etal, 2001b)indicated thatwheat cropsinextensive crop
rotationsoflongduration farms had alowabundanceofherbivores and amoderately high
abundance ofdetritivores (i.e.smalldipteraspecies) andparasitoids,whereaswheatcropsof
intensive croprotation farms werecharacterised by(potential) outbreaks ofr-herbivores and
absenceofhigh numbersofotherarthropod functional groups.
Theideaspresented correspond tothehypothesis ofPoweretal.(1996),thatpartly
contradicts thehypothesis ofthepositiverelationbetweenincreasedprimary productivity and
toppredation (e.g. Oksanenetal, 1996).Poweretal.(1996)found intemporal successionon
riverflood plains,that food chains shorten from threetotwosteps,because inalater
successional stage armoured secondary consumers inhibit food supplyofthetoppredators;in
thedynamic situation ofearly successional stagetheprimaryorganisms arebetter accessible
andgiverisetolonger food chain lengthsmorethantwo steps.Inmore orless stabilized farm
food websduetodetrital subsidy andherbivory-resistant cropphysiology, dominant
predacious invertebrates maybe epigeicpredators.Thisguild is'armoured' from abirds
perspective;their'armour'mayrelatetobothhardbodies (carabids) aswell ashidingindense
71
vegetation orinthesoil,size(e.g.forwagtails) andnocturnalbehaviour (Vickerman&
Sunderland, 1975).
4.3. EcologicalInfrastructure effects
Territory densitiesofmost investigated bird functional groups showed thepositive effect of
increased numbersofdetritivores andpredators inlatemown E.I. (Table 10).Accordingly
increased arthropod abundance in latemown (uncut)vegetation, ascompared to earlymown,
isreported inseveral studies (Boatmanetal, 1999;Wakeham-Dawson etal.,1998;
Schekkerman, 1997;Curry, 1994).Wagtails/pipetmayhave foraged onabundant small flies.
Negativerelations ofbirdstoparasitoids andK-herbivores indicated anavoidance ofearly
mown E.I.becausethesegroupswererelatively abundant intraditionally managed canal
banks(Smeding etal.,2001b).However, skylarks alsoshowed some affinity for openE.I.,
possibly attracted byhoppers,lycosid spiders,granivorous carabids andants.
Apart from marshbirds,thereisatendencytoavoidhighE.I.vegetation. Thismayhavea
behaviouralbackground thatthetypical arable farmland birdsprefer habitatsthat afford a
goodview.Marshbirdsdidnotrelate stronglytotheaveragevalueofE.I.vegetation height
becauselocal standsofreed orshrubsmay alreadybe sufficient toestablish anumberof
territories.
Emergent vegetations mayattractorcatch flying arthropods (Hradetzky &Kromp, 1997).
Manydetritivorous dipteraand aphids inlate-mown vegetation areperhapsnot autochthonous
forthehabitat. r-Herbivores density intheE.I. andcrop areawerehighlycorrelated (Smeding
etal.,2001b).Thismayexplainwhymarshbirds,whichmostly stayinandaroundE.I.
vegetation, couldbepredictedbyr-herbivores intheE.I.and, intensiveproduction indicating
(Smeding etal, 2001b),small staphylinids inthecroparea.Densities ofmarshbirdsin
emergent vegetation surrounded byarablecropsmightbepromoted byaprey 'precipitation'
ofbothdetrivoresandherbivores from thecroparea.
Hald&Redderson (1990)notedthat additional sweep-net sampling,includingmorebirdprey
items,exaggerated thedifference between conventional andorganic crops.Accordingly
catchesoffour yellowwatertrapsonfarm E(Venhorst &Smeding, unpublished data)
included taxaunderrepresentedby suctiontrapping,containing 75%dipteraofwhich c.10%
involved largertaxa(>2mgdryweight).Thisunderrepresented group,involving anthomyid
flies, scatophagid flies, craneflies andpredacious flies mightbeimportant for various
insectivorousbirds (Poulsen etal, 1998;Cramp, 1988).
Soil life-feeding birdswereexpected torelatetocrop areacharacteristics. However, also
association with certain E.I.characteristicswere found. This isinaccordance with
impressions inthefieldthat chicks oflapwing often occurred inditches,particularly those
with 'traditional mangement',wheremudand shallowwaterinnon-vegetated open ditch
bottomsprovide soft ground andabundant aquaticprey,includingmolluscs.
4.4.Landscape effects
Differences inbirdterritory densitiesbetween farms were alsoaffected by landscape factors.
TheZuid Flevolandpolderhad ashorterlife and largerfieldswhichmeans alowerspatial
density ofE.I.Territory densities ofskylarks,wagtails/pipet, linnet andlapwingrelate
positively tooneorboth ofthesevariables andtherefore olderpolderswere preferred.
72
Negativerelationstolinyphiid spiderscanbeexplainedbythefact that linyphiids preferred
the larger scale found intheyoungerpolder(Smedingetal, 2001a).
Atthelandscape level skylarks seemedtobe associated with ahighproportion ofgramineous
cropsand alowproportion ofvegetablecrops.Thiswasmoreorlessoppositetothe farmlevelobservations ofskylarksbut inaccordancewiththeexpectation from literature.
Landscape level crop areasincludedboth conventional andorganiccrops.On conventional
farms cerealsmayoffer thelargest food resource forbirds.However, onorganic farms other
cropsthan cerealscouldberelevant for preyprovision.
Accordingtoexpectations,marshbirdswereenhanced byahighpercentage of semi-natural
habitatsinthefarm surroundings.Impressions inthe field werethatvicinity ofcanalswith
reed stands,ponds ordense shrubs {e.g. ina2hanaturereservenear farm A) encouraged
nesting ofthis functional group inthe farm E.I.However, total songbird territory density is
related negatively totheproportion ofsemi-naturalhabitat atthelandscape level.Accordingly
spatial analysisof skylark observations with GIS(Nanetal.,inprep.)revealed that skylark
territories areclustered onfarms,particularly at somedistance from the farmyards, treelines
androads.Thismayreflect thepreference shownbytypical arablefarmland birdsfor open
landscapewithnodisturbance.
4.5. Conclusions
Resultsofbird studies in 1998and 1999ontenorganicarable farms inFlevoland suggestthat
birdterritory density isparticularly supported byorganic arable farms with intensivecrop
production and improved (latemown,speciesrich) ecological infrastructure. Bird food
resourcesonintensive farms maybebasedonperiodic andlocalherbivore increasesinacrop
mosaic.Extensive systemsmightbemorebalanced duetothepest-control bybeneficials (i.e.
polyphagouspredators) andtoalesssusceptible cropphysiology. However, inthese systems
with greaterdetrital subsidized food webs(cf.Wiseetal, 1999),thehigher trophiclevels(i.e.
insectivorousbirds)mightbe inhibited bysecondary consumerswhich exploittheprimary
level andhave limited availability for vertebratepredators (cf.Poweretal, 1996).
Cropareasonorganic arable farms inFlevoland maynotresemblethe food rich habitats
observed byHald&Redderson (1990)orinset-aside (e.g. Poulsen etal.,1998)dueto
perhapsintensity and/or abundanceofepigeicpredatorsthatinhibitpopulationsof soft-bodied
herbivorous larvae.
LatemownE.I.mostprobably offers animportant food resource, supplementing both
quantitatively andqualitatively, thecroparea food resources andpossibly filling temporary
gapsinfood availability.
Ourobservationsprovided preliminary evidence fortheseideas;further research isrequired.
4.6. Recommendations
Furtherresearchonthetopicrequiresrestricted geographical variationbetween farms.
Experimental manipulation ofbirdpopulations atthe farm level isextremely expensive.The
study areamaytherefore includeextremetypes ofcommercial farms, with regard to intensity
andE.I.management andoneortwoexperimental (pilot)farms whichhave,for example,
increased detrital subsidybased oncropresidues andorganicmanure.
73
Thesuggested importanceofr-herbivores forbirdsinthecropareaishardtotranslatein
practicalrecommendations becauser-herbivores areusuallypests.Itmay therefore bea
challenge for farmers andagroecologists todesign croprotationswithcontrolled herbivory in
for examplemixed crops,livingmulches (Theunissen, 1994;Theunissenetal, 1997),ley
cropsand grazing-resistant cultivars.
Closerexamination oflocalbirddietsand foraging habitatsisrequired, assessing the
contribution ofaphids,craneflies andcarabidbeetlesinbird diets,andtracing important taxa.
Othercatchingmethods,preferably including adensity assessment, shouldbetried(e.g.
Duellietal., 1999).Alsonon-food habitat factors (machinedisturbance andpredation) should
beconsidered.
Specialattention shouldbegiventotheeffect oflocal'hot spots'offood, represented by
wagtails feeding ondungdeposits(e.g. Hald&reddersen, 1990)or lapwings feeding atditch
bottoms.
Modification byfarmers ofE.I.management isveryrewarding intermsofbird abundance
andtherefore ofnatureconservation value.Inparticularbecause latemowingcontributesto
bird food resourcesinearlysummer. However, managementswithcautious, frequent mowing
at>10cmaboveground surface may also stimulateherbivores andpredators important for
birds.Optimallymanaged E.I.mayincludeapermanent, simpledivision into some frequently
mownandlatemownboundaries (seee.g. Feberetal.,1999)and also local,broad standsof
tallvegetation orshrubswhich facilitate nesting ofmarshbirds (seee.g. Stoate, 1999).Reed
orshrubsshouldpreferably be situated closetothepresent semi-natural habitat sothatopen
space,attractive for typical farmland birdswillnotbecome fragmented (Smeding &Joenje,
1999).
Acknowledgements
Theauthorswish tothankthe farmers whoallowed usaccesstotheirland.Thanksaredueto
AndreMaassen (Unifarm) and Clasien Lock (PRI)for technical assistance,DrA.J.Beintema
(Alterra) andWouter Joenje (WU)for discussing ourwork during aoneday field visit,and
BartVenhorst, BertusMeijer andJanNoorlander for arthropod measurements. Theworkat
theWageningenUniversity isfunded bytheMinistry ofAgriculture,NatureManagement and
Fisheries,Department ofScienceandKnowledge Dissemination.
74
Chapter 5:Effect offield margin management on insectivorous
birds,aphids andtheir predators indifferent landscapes
F.W.Smeding"&C.J.H.Booijb
"Departmentof Plant Sciences, Biological Farming Systems group, Wageningen University, Wageningen,
TheNetherlands
1
'PlantResearch International, Wageningen, The Netherlands
Abstract
An increased field margin area at farm level, isthought topromote vertebrate and arthropod predators and to
reducepests.In afieldtrial in 1997acomparison was madebetween animal communities on four organic farms
thatpossessed different amounts of ecological infrastructure (E.I.)- O n e P 3 ^ w a s situated inyoung landscape and
the other inold landscape. Only specialist insectivorous birds showed aclearpositive relationship. With regard
toimportant arthropod species inwheat (e.g. carabid, staphylinid and coccinellid beetles, spiders) abundance
differences inrelation toamountofE.I. werenotrelated toold andyoung landscapes. High aphidophagous
syrphid fly abundance and aphid (pest) densities occurred inyoung landscape farms.
1.Introduction
1.1. Agricultureandbiodiversity
Biodiversity inEuropeanagricultural landscapesisdecreasing.Oneimportant solution for
reversingthisbiodiversitylossistodevelopfarming systemsthatintegrateagricultureandnature
conservationinterests.Organicfarmingtriestoimplementthisideabecausebiodiversityis
thoughttoenhancepestcontrol(Altieri, 1994). Farm-natureplanssupportthesefarmstodevelop
site-specifichabitatdiversification whichmeanstheestablishmentofanecological infrastructure
(E.I.)(Smeding&Joenje, 1999).TheE.I.isdefined asthetotalofsemi-natural (aquatic,woody,
tallherbandgrassy)habitatsonthefarm includingitsspatialarrangement.Habitat
diversification islikelytoincreasenaturalenemyabundanceandtoreducepestpopulations
(Booij &DenNijs, 1996);thismeansthattheherbivorouspestorganismsrepresentasmallpart
ofthemainlynon-pestherbivore anddetritivorecommunitiesinthefarm foodweb.Theincrease
ofbeneficial andharmless(prey)speciesenhancesthefood availabilityforthevertebratespecies
onthefarm(e.g. Moreby&Sotherton, 1997; Hald&Reddersen, 1990),whichareof
conservationinterest.
1.2. Farmecologicalinfrastructure
PracticalrecommendationstooptimizetheEcological Infrastructure often relyonexperienceand
commonsense.Detailedstudiesaboutkeyspeciesareavailable,e.g. skylark(Wilsonet ai,
1997)andpartridge(Potts, 1983),however,itisdifficult tocombineandextrapolatethis
knowledgetofarm practiceandtranslateittoactionsofthe farmer.
Ourstudywasintendedtocontributetoasystemsapproachthatlinksinformation ontheecology
ofspecies(groups)withfarmtopographyandmanagement.Therefore weundertooka
simultaneousexamination ofseveralintegrationlevels(landscape,farm andhabitat/field) and
animalspeciesgroups.Farmandfaunameasurementswhicharebotheffective inthefield(Den
Nijsetai, 1998)aswellasexplanatoryfactors infuture theorywereselected.
75
Inafieldtrialin 1997acomparisonwasmadebetweenfourcontrastingorganic farmsthat
possesseddifferent amountsofestablishedE.I.andmightserveasgoodexamplesfortheabove
theory.Itisprobablethattheeffect ofequalefforts bythefarmerwoulddiffer between
landscapes;abiodiverseneighbourhoodmayoverruleoramplify theeffect. Therefore onepair
oforganicfarms wassituatedinayoung(culture) landscapeandanotherpairoforganic farmsin
anold(culture)landscape;oldlandscapeisassumedtobemorebiodiverse.Ourhypothesiswas
thatanincreasedE.I.wouldbeassociatedwithmoreinsectivorousbirds,morearthropod
predatorsandareducedpest infestation.
2.MaterialsandMethods
2.1.Studysites
Theresearchwascarriedoutonfour different organicfarms(indicated inthetextasY-,Y+,Oand0+) onclaysoilsinApril-August 1997.Twofarmsweresituatedintheyounglandscape
(=Y)ofthepolderZuid-Flevolandwhichwasreclaimedin 1968.Theothertwofarmswerepart
ofanoldlandscape(=0)neartheriversinthecentreofTheNetherlands.Ineachlandscape
farmswithasmallE.I.(=-)andafarmwithagreaterE.I.(=+)wereselected.Withineach farm
winterwheatfieldswerechosenasarepresentativecropforarthropodandarableweed
measurements.Cerealaphidswerechosenasanexampleofapest.
ForDutchstandardsallstudied farmscanbeconsidered asoldorganicfarms.FarmsY-andY+
startedin 1985onanexperimentalreclamationareawhichneverreceivedpesticides.FarmY+
joined agroupof 10'innovation'pilot farmsin 1993 whichimpliesthatallditcheshave adjacent
threemeterwidegrassstripsandthatditchvegetationincludesseveralartificially introduced
indigenousplantspecies(Vereijken, 1998). FarmO-convertedtoorganicfarming practicein
1980;itsintensiveproductionisfocussed oncabbageandleek;oldhedgerowsweremaintained,
mainlyatthebordersofthefarm.Farm0+ wasrunbetween 1971-1995aspartofasecondary
schoolforbiodynamicfarming; extensiveboundariesincludinghedgerowswerecreatedduring
thisperiod.
2.2. Samplingandmeasurements
2.2.1. Landscape
Landscapeparametersweresampledinacirclearoundthemathematicalcentreofthefarm.The
radiusofthiscirclediffered betweenthefour farmsbecauseitincludedasectionofthefarmand
anextra200mfromthefarmborder;the200mdistanceapproximatestothehomerangeof
severalsmallmammalsandsongbirds.Insidethecircle,theareaofdifferent agricultural,seminaturalandotherhabitatswasmeasured.Thesemi-natural aquatic,woody,tallherbandgrassy
habitatsweredefined asE.I.Thescaleofthelandscapewasdeterminedbymeasuringthetotal
areas("blocks')ofinterconnected agricultural fields.
2.2.2. Farm
Thelimitsofthestudyareawereequaltotheadministrativebordersofthefarmbecausethisis
theunitarysystemundercontrolbythefarmer (Swift &Anderson, 1993).Theareasofseminaturalhabitatsweremeasured, asforlandscape.
Thespatialarrangement oftheecologicalinfrastructure wasexpressedbythepercentageofthe
farmwhichlaywithina 100mdistanceoftheecological infrastructure. Theinfluence ofboundariesontheabundanceoflargecarabidbeetlesandspidersprobablydoesnotexceed 100m.
76
2.2.3. Vegetation
Vegetationstudiesincludedboundariessurroundingthecrops.Theherblayerwassampledin
onemeterlengthsatintervalsof25-100mbetweensamples,dependingonthelengthofthe
boundary.Parameterswere:cover,maximumheight,plantspeciesanddominantplant species
(whichdetermine 80%cover).
Weedspeciescomposition inwinterwheatwasrecordedbylistingthespeciesin40samplesof
0.25m ineach field.
2.2.4. Birds
Territorymappingofbirdswasdonethreetimesatthebeginning andtheendofMayandthe
beginningofJune,usingthemethoddescribedinVanDijk (1993).Breedingbirdsweregrouped
accordingtothreefood types:insectivorous,insectivorous/granivorous andsoil life-feeding.
2.2.5. Arthropods
Weeklysamplesweretakenoneachfarm inwinterwheatbetween29Apriland24July.Ineach
winterwheatfield fourrandomplotsof 10by20mwerelaidout,inwhichthreepitfall trapsand
ayellowwatertrapwereplaced.Aphidswerecountedon80to200tillersperplot,dependingon
theexpectednumberofaphidspresent.Thecarabidandstaphylinidbeetlesandspiderscaughtin
pitfall trapsweresortedintosizecategories;syrphidflies andcoccinellidsinthewatertrapswere
determinedtospecieslevel.
InSeptemberthreesuctionsamples(3minutesin 1 m2)werecollectedinadjacent boundaries
includingatallherbandgrassyandashrubsample;herbivorousbeetles(curculionidsand
chrysomelids)weredeterminedtospecieslevel.
3.Results
3.1.Landscapecharacteristics
3.1.1. Farmsurroundings
Theyounglandscapewasdominatedbyagriculturallanduseandhadlargeblocksofcontinuous
agriculturalland(Table 1).Thepercentagesemi-naturalhabitat appearedtobeunaffected by
landscapetype.
3.1.2. Farmandits habitats
Croprotationinyounglandscapetendedtoincludefewer extensivecrops(cerealsandley
pasture)(Table 1),howeverfarm Y-includedarelativelylargepercentageduetoitslargesize.
Wheatyieldswerehigherintheyounglandscapewhereasarableweedsinthiscropweremuch
moreabundantanddiversintheoldlandscape(Table 1).Farmsinyounglandscapehadalarger
cropareathatwasremotefrom theboundaries(Table 1).Boundariesinthepolderincludedmore
aquatichabitat(ditchesandbanks)andintheriverregionincludedmorewoody(hedgerow)
habitat.Thestructurediversityandspeciesrichnessoftheboundaryvegetationappearedtobe
unaffected bythelandscapetype(Table1).
77
Table 1
Characteristicsoffourfarms inyoung (Y) andold(O)landscapewithsmall(-) orincreased(+)E.I.withregardto
landscapeandhabitats.
Y-
Y+
O-
0+
Landscape
%agricultural landuse
block size (average)(ha)
% semi-naturalhabitat
71
23
27
94
26
4
54
3
40
52
2
18
Farm
farm area(ha)
% cereals/leypasture incroprotation
% farm areawithin 100mrangeofE.I.
% semi-natural habitat=E.I.
10
50
61
1.2
55
29
72
2.6
22
50
81
1.7
28
75
100
5.8
Crop
no.ofweedspecies/0.25 m2
3.2
1.6
5.4
5.1
Boundary
no.ofplantspecies/m (average)
7.6
11.4
9.0
9.9
3.2. EffectsofEcologicalInfrastructure
3.2.1.Younglandscape
CharacteristicsoffarmY+(2.6%E.I.)incomparisonwithfarmY-(1.2%E.I.)were:amore
diverseboundaryvegetationandlessweedsinwheat(Table 1);ahigherdensityandspecies
numberofbreedingbirdsduetotheoccurrenceofspecialistinsectivoresintheboundaries(Fig.
la);aslightlygreaterabundanceofmostpolyphagouspredatorgroupsinwheat(carabids,
staphilinidsandlycosid spiders)(Figs lb and lc),whereasaphidophagous syrphidsand
ladybirdswereslightlymoreabundantinwheatonfarmY-(Fig. lc);similarhighaphid
abundanceinwheat(Fig. Id);ahigherspeciesnumberandsimilar(low)abundanceof
herbivorousbeetlesinboundaries.
3.2.2. Oldlandscape
Characteristicsoffarm0+ (5.8%E.I.)incomparisonwithfarm O-(1.7%E.I.)were:amore
diverseboundaryvegetation(Table 1);ahigherdensityofspecialistinsectivorousbirdsanda
lowerdensityofmixedinsecti-granivorousbirdsresultinginalowertotalbreedingbirddensity
(Fig. la);lowerabundanceofpolyphagousaphidpredatorsinwheat(carabidandstaphilinid
beetlesandlinyphiid spiders)(Fig. lb);monophagousaphidpredatorabundancewerevariable:
moresyrphids,lessladybirds(Fig. lc) andlesslacewings;similarlowaphidabundanceinwheat
(Fig. Id)apartfrom anearlymoderatepeakofMetopolophium dirhodum; ahigherspecies
numberandabundanceofherbivorousbeetlesinboundaries.Theabundanceofsyrphidscould
havebeenunderestimatedbecausetheyellowwatertrapscompetedwithnumerous flowers
(DenNijsera/., 1998).
3.2.3. Relationshipswith landscapetypes
Increasedecologicalinfrastructures ontwoofthefour farmsintwocontrastinglandscapetypes
involvedadoubledpercentageofsemi-naturalhabitatsandamorediversevegetation(Table1).
ThispromotedinbothlandscapesspeciesthatstronglydependontheE.I.itself(insectivorous
birdsdensityandherbivorebeetlesdiversity).InthecroponlyabundanceoftheaphidR.
dirhodum seemedtoincrease(Fig.Id).Adecreasewasfound withregardtotheabundanceof
coccinellids(Fig.lc)andthedensityoftheaphidSitobion avenae(Fig.ld).Howevermost fauna
parametersthatwerestudieddidnotshowarelationship.Abundanceofpolyphagousaphid
predatorsonfarmswithincreasedE.I.decreasedinoldlandscapewhereastheyincreasedin
younglandscape(Fig.lb);aphidophagoussyrphidsshowedthereverse(Fig.lc).
78
a. Birds: number ofterritories perha
0.8
0.6
0.4
0.2
0
Y+
• insect feeding
ETP
o-
o
Hinsect/seed feeding
b. Polyphagous predators: total no.in pitfalls
12000
8000
4000
n±±
Y+
- 1
0+
O
ICarabidae HLycosidae •Linyphiidae D Staphylinidae
600
c.Aphidophagouspredators:totalno.inyellow
watertraps
400
200
HbzLJHbl3__JBS3_:
Y-
Y+
IaphidophagousSyrphidae
O-
0+
DCoccinellidae
d.Aphids: sum of the average no.per tiller
75
50
25
SEfcE
Y+
iMetopolophium dirhodum
Oo+
OSitobion avenae
Fig. I. Occurrences of birds (a),polyphagous predators (b),aphidophagous predators (c),and aphids (d)on
four farms: Y=young landscape; O =old landscape; - =small ecological infrastructure; += large ecological
infrastructure.
79
4.Discussion
Onlyobservationsofspecialistinsectivorousbirdsandintheyounglandscapealsopolyphagous
predatorssupportedourhypothesis.Fewparallelsbetweeneffects intheoldandyoung
landscapeswerefound. Howcanthesecontradictoryresultsbeunderstood?Inourattemptto
giveanexplanationwefocusonsoilinvertebratesandweedabundancewhichareonlygroups
amongseveralothers.However,thesegroupsarelikelytoinfluence numbersofbirdsand
predatoryarthropods.
4.1. Younglandscape
Soilsinthepolderlandscapeareknowntocontainfewearthwormsandprobablyhavealower
soilmeso-andmacrofaunabiomassthanoldlandscapes.Thisisinaccordancewiththeobserved
lowdensityofsoillife-feeding birds.Thelowabundanceofarableweedslimitsdependent foliar
herbivoresandgranivores.Thesefactors leadtoacrophabitatwhereaphidsbecomean
importantcomponent inthesummerdietofpolyphagouspredators(Booij &DenNijs, 1996).
Severalauthorsreportthispredominanceofaphidsinconventionallymanagedwheat(Moreby&
Sotherton, 1997; Reddersen 1997).
PredatorcountsonfarmY+suggestedaninfluence ofincreasedE.I.butitsareamayhavebeen
toosmallanditsdistancefromfield centrestoofartohaveastrongeffect; moreoverweed
abundanceandahighpercentageofcereals/leypastureonfarmY-offered bettercircumstances
forgrounddwellinginvertebratesascomparedtofarmY+.
4.2.Oldlandscape
Cropsintheoldlandscapecontainedmoreweedsandprobablyahighersoilinvertebrate
biomass.FarmO-hadahighweedabundance;itsintensivevegetableproduction causedahigher
generalfertility levelofthefieldswhichmayhaveaquantitativeeffect onsoilinvertebrates.
Thesefactorscouldexplainthehighabundanceofthepolyphagouscarabidbeetles(comparable
withtheyounglandscapenumbers)andlinyphiidspidersinspiteoftheabsenceofaphids.Also
theapparentlyhighabundanceofinsectivorous/granivorousbirdsatfarm O-supportsthisideaof
abundantfoodavailabilityinthefields.TheserequirementspossiblyoverruletheE.I. influence
oncropcommunitiesinthegrowingseason.
4.3. Improvingthehypothesis
Inthelightoftheseresultsweconcludethatthehypothesisshouldalsoconsidercrop factors
includingcropdiversity(e.g.croprotation,weeds)andsoillifecharacteristics.Ideally
comparativeresearchonE.I.influence shouldberestrictedtofarmswherethesecharacteristics
aresimilar.Thehypothesiscouldonlyworkonfarmswithintermediatelevelsofalternativeprey
onthefields (associatedwithsoillife andweedsorintercrops)andwithboundariesthatarenot
toofarfromfield centres.Inourstudyin 1997itseemedthatanimalcommunitiesinthecrops
wereindependentfromE.I.Inthepoldertheintensivelycroppedfieldswereprobablytoolarge
tobeinfluenced bytheE.I.whereasintheriverregionthefields alreadyhadahighlevelof
alternativepreyrelatedtocropfactors.Withabundantalternativepreycausedbycrop factors
(whichmightbeundesirableforthefarm,e.g. weeds)asmallerE.I.mayalreadybesufficient to
maintainbiodiversity.
80
Acknowledgements
Theauthorswishtothankthefarmers whoallowedusaccesstotheirland.Thanksaredueto
ClasienLock(PRI)andAndreMaassen(Unifarm) fortechnicalassistance,Jan-PietZijpand
ElkeBoesewinkel forarthropodmeasurementsandLoesdenNijs forassistanceindesigningthe
experiment.TheworkattheWageningenUniversityisfunded bytheMinistryofAgriculture,
NatureManagement andFisheries,DepartmentofScienceandKnowledgeDissemination.
Chapter 6:Aconcept offood webstructure inorganic arable
farming systems
F.W. Smeding*&G.R. deSnoob
"DepartmentofPlant Sciences, Biological Farming Systems group, Wageningen University, Wageningen,
TheNetherlands
b
CentreofEnvironmental Science, UniversiteitLeiden, Leiden, The Netherlands
Abstract
Aproposal for adescriptive ortopological farm food web isderived from field observations and from references
inliterature.Important themes in the food web theory aretentatively applied tothispreliminary model,
explaining differences between localfarm food web structures andhow they arerelatedto farm and/or
ecological infrastructure (E.I.) management. Predictions aremade for four different farm food web structures for
extremes of farm and environmental gradients corresponding tothe length of organic duration and
amount/quality of E.I.The implications with regard tofarming practices andnature conservation arethat both
organic duration and the amount/quality ofecological infrastructure may contribute toecosystem services and
nature conservation. However, an optimisation ofthe farm food webwithregard toecosystem services, may
possibly run counter tonature conservation goals.
1. Introduction
1.1.Theproblem ofbiodiversitylossin agroecosystems
Speciesdiversity ofindigenousplantsandanimalsonfarmland isdecliningdramatically due
toagricultural intensification (Paoletti, 1999;Wood &Lenne, 1999;Vandermeeretal.,1998;
Swift &Anderson, 1993).Amongst thosethataregreatlyconcerned aboutthisbiodiversity
loss areagriculturists, ecologistsandmembersofthepublic.Nature conservation
organisationsusuallyaddresstheintrinsicvalueofbiodiversity andtheirviewpoint is
translated intonationalprograms for speciesandhabitat conservation (e.g.inThe
Netherlands:Baletal, 1995).Agroecologists stresstheeconomicvalueofbiodiversity,
relatedtoitsecological services,e.g. pest control andbioticregulation ofsoilfertility (Altieri,
1994, 1999;Paoletti, 1999;Pimenteletal, 1995).Biodiversity losshasbeenthought toresult
inartificial ecosystems,requiring constanthuman intervention and costlyexternalinputs.
Ecosystem servicesmightbesustained orimprovedbyageneral,indiscriminate,high species
diversity (Altieri, 1994;Paoletti, 1999)orbyafew essentialcomponents ofthelocal
biodiversity, asdetermined bysitecharacteristics (Vandermeer etal, 1998;Almekinderset
al, 1995).Functional redundancy ofspeciesmeansthatnot all specieshaveevident
significance for ecosystem services(Duellietal, 1999).However, itcanbe arguedthat
agriculturehas,toacertain extent,responsibility for allspeciesand communitieswhichcoevolvedwith farming during around 10,000years(Wood &Lenne, 1999),irrespectivetheir
utility.
1.2. Multi-species agroecosystem research
One important solution for the reversal of the loss ofbiodiversity in agriculture of the
industrialised countries is the development of farming systems that are economically based on
83
utilisationofbiodiversity andthat harbour,partly duetoincreased biodiversity, conservationworthy species.Thisideaiscompatibletotheconcept ofmulti-species agroecosystems
(Vandermeeretal, 1998;Altieri, 1994, 1999;Almekindersetal, 1995;Swift &Anderson,
1993).
Research aimed atthisconceptrequires anappropriate approach;threecriteria,whichtake
into accountthestudied objects andenvironmental variables,mightbeessential.Firstly,the
research shouldapplymethodsthat areappropriate forhigher levels ofaggregation andavoid
reduction ofthesystemthroughemphasisonvariablesof lower levels (Almekinders et al,
1995).Secondly,investigations should addressreal farming systemsbecause biodiversity,
relevant for apparent ecosystem services,mightbe site-specific (Vandermeer etal, 1998)and
maynotbeobservableinsmall 'isolated' subsystems,orforeseeable by abottom-up approach.
Preferably study areasshouldincludeobjects that express functioning ofecosystem services
(Brown, 1999a).Thirdly,assessed variablesshouldbeclearly related toboththe structural
andthedailydecisionsofthe farmer sothattheoutcomescanbetranslated into farming
practice andpolicy {e.g. Vereijken, 1997;Kabourakis, 1996;Park &Cousins, 1995;Smeding
&Joenje, 1999).
Recent advances inresearch onfood webs(Polis&Winemiller, 1996)offer asuitable
approach forbiodiversity studies athigher levelsof aggregation (Pimm,1991;
Gezondheidsraad, 1997).This articletherefore examinestheperspectives ofafood web
approach forresearch that aimsatmulti-species agroecosystem development.
1.3. Foodwebapproach
1.3.1. Definitions
Definitions andgeneral information onfood webshasbeen examined extensively inthe
volumeeditedbyPolis&Winemiller (1996);someoftheirmainpoints aresummarisedhere.
Afood webisdefined asanetwork ofconsumer-resource interactions among agroupof
organisms,populations,oraggregate trophicunits.Speciesareusually aggregated in
'trophospecies' or functional groupswhich essentially shareresources andpredatorsbut
usuallymorecriteriaareusede.g. life historytraits.Guildsaretrophospecies ofahigher
order, andusually includeseveralrelated functional groups.
Inafood webdiagram functional groups arearranged introphic levelswhichhavethesame
number ofsteps('chainlengths') awayfrom thebasalresourcesplants ordetritus.A
descriptiveor'topological food web'depicts species and feeding relations;ina'flow web'
components andrelations arequantified astonumber orenergy flow. Themost elaborate
food webrepresentation isa'functional web'that alsorevealstherelative strength ofrelations.
1.3.2. Researchonfarmfood webs
Traditional studieson farmland communities often included considerations ofthetrophic
structurewhich indirectly addressed local food webs.Examplesofthiskind of studies arethe
comprehensive empirical studybyPotts&Vickermann (1974),including awiderangeof
invertebrate andvertebratetaxapresent inwheat cropsinWest Sussex,UK,orthe extensive
surveyofthetrophicstructure ofabove-ground insectbiomassinvarious agricultural
landscapesbyRyszkowski &Karg(1991)andRyszkowski etal. (1993).
Most studiesdirectly addressing food webswererestricted toapartofthe farmland
community, involving asection oftheherbivore food (sub)weborasection ofthedetrital
(sub)web,for examplestudiesofpest-predator complexes (examplesine.g. Wood &Lenne,
1999;Kromp&Meindl, 1997)orthestudiesof food requirements offarmland birds
84
(reviewed byPoulsenetal, 1998).Someofthesestudiesprovided clearconceptual advances.
ForexampleAndow (1988)hypothesised 7'primitiverelations'(i.e.food web structures)
amongweeds,crops,herbivoresandpredators.Comprehensivetopological foodwebsof
arablecropping systems,includingdetrital andherbivore subwebs,werefirst developed in
1977forrice,inthecontext ofIntegrated PestManagementprogrammes (e.g. Cohenet al,
1994;Schoenlyetfa/., 1996).
Amajorbreakthroughinagroecological applicationoffoodwebtheory,werestudiesonthe
detrital subwebsinarablecrops(e.g. DeRuiteretal, 1993,1995)andgrasslands(e.g. Hunt
etal, 1987),including alsoanalysesofnutrient andenergyflows. Progressin scientific
understanding offoodwebsisexpandingintoagroecosystems asisdemonstratedbyseveral
recentreview articles,for example:detrital subwebcontrol oftheherbivore subwebby
influencing vegetationperformance (Brussaard, 1998)orbyincreasedpredatorpressureon
herbivoresduetoexternally subsidised detrital chains(Wiseetal, 1999);and interference
betweenpredacious functional groups,causing 'trophiccascades'intheherbivore subweb
(Tscharntke,1997).
1.4. Objectives
However, despitetheabove-mentioned advances,thereis,toourknowledge,no
comprehensive farm food web available for arablefarming systems.Sucha'topological' food
web,oramoreelaborate'flow' web,mayenable asynthesisof fragmented dataontaxaand
habitats,andcouldsubsequently form thefoundation ofagroecological farming system
research (e.g. Swift &Anderson, 1993;VanKeulenetal, 1998)aswell asapplied
agroecosystemplanning (Smeding &Joenje, 1999;Visser,2000).
Theobjectives ofthisarticleare:
-toproposeasimplified topological farm food web,encompassingbothherbivoreanddetrital
subwebsandtheirinterrelations,asoccurring atthe farm levelof aggregation;
-todemonstrate,usingbothempirical dataandtheory,howthispreliminary food webmodel
couldbeusedtorelatetheabundanceoffunctional groupstofarm management;
Acasestudywillbeusedtomeettheseobjectives.
2.Methods and materials
2.1.Researchareaanddelimitation ofthesystem
2.1.1. Organicarablefarms in Flevoland
Theagroecosystem ofarablefarms inFlevoland iswellstudiedbecause ofseverallarge
experiments(e.g. Booij &Noorlander, 1992;Booij, 1994;Brussaardetal, 1988,1990;De
Ruiter etal, 1993,1995;Lantinga &Oomen, 1998;Smeding &Joenje, 1999;Remmelzwaal,
1992;Remmelzwaal &Voslamber, 1996;Vereijken, 1989,1997,1998).Flevoland consistsof
threepoldersthatwerereclaimedbetween 1940and 1968andaredominatedby agricultural
landuse.Thelandscape isflat andopenwithwoodlotsconfined to farmyards, villagesand
mainroads.Thepredominant soiltypeiscalcareous clayofmarineorigin.
Organicfarms may function asastepping stoneontheroadtodeveloping multi-species
agroecosystems (e.g.Stobbelaar &VanMansvelt,2000;Vandermeer, 1995)andwere
therefore chosenasobjects forthecasestudy.Around 75organicfarms aresituatedin
Flevoland including farms withimproved ecological infrastructure, resulting from a
85
prototyping researchproject (Vereijken, 1997, 1998).Thecasestudy isbased on empirical
dataof 17organic farms andoneintegrated farm, and literature concerning around 10
organic,integrated andconventional (experimental) farms.
Croprotationsoforganic arable farms inFlevoland includesixormoreyears.Commoncrops
arespringandwinterwheat (10-35%),leypasture(0-20%),traditional lifted crops (potatoes
and sugarbeet)(10-35%) andintensivevegetable crops (25-70%).Major vegetable cropsare
onions,peas,sweetcorn,runnerbeans,carrot andvariouscabbages.Ploughing isgenerallyat
25-30cmdepth.Theecological infrastructure (E.I.)(Smeding &Booij, 1999)onarable farms
inFlevoland mainlyconsistsof linearherbaceous boundaries ofcanalbanks andvergesalong
tracks androads (Smeding &Booij, 2001).Thecasestudy isbased onempirical dataof
around20organic farms.
2.1.2.Delimitationofthesystem
Thefarming systemispositionedbetweencommonlyrecognised aggregation levelsofhabitat
and landscape andmaytherefore betoosmalltobeconsidered asan(agro) ecosystem.
However Swift &Anderson (1993)considerthe farm asthebasicunit in studiesofsystem
functioning inagricultural systems.Thefarm levelmighttherefore beconsidered as
aggregation level intheecological sense.Accordingly,Bockemuhl (1986) arguesthat taking
localecological andhistorical factors intoaccount infarm management canconsolidate the
systembordersofafarm unit.
Thesecondcriterion for spatialdelimitationoftheconsidered systemisthatitmatchesthe
spacerequiredby awell-defined food web.AccordingtothesecriteriaCousins(1988)
defined theEcosystem TrophicModule:theETMisbased ontheterritory sizeofthetop
predator.Resident toppredatorsonarable farms inFlevoland areKestrel (Falco tinnunculus)
and Stoat {Mustela ermined) (Remmelzwaal &Voslamber, 1996).Theirterritory sizes
correspond tothescale andsizeofthestudied farming system.
2.2.Generaldescription ofthetopologicalfarmfood web
Thetopological food web,includingpreliminary flow webcharacteristics,ofaFlevoland
organicarablefarm wasdeveloped usingthe following sourcesof information:
- empirical data from farmland speciesinFlevoland includingdata from ourownresearch
inFlevoland (references mentioned above andSmeding etal, 2001a,2001b;Smeding&
Booij, 1999,2001; Smeding,unpublisheddata);
- literatureondiets andpredatorsofthetaxaobserved in Flevoland;
- publications ofresearchconcernedwith farmland speciesinarablecrops andfield
margins inWestern Europe.
Thespecies (-groups) were listed inafood webmatrix.Functional groups andguildswere
assembled accordingtocommonly accepted criteria (Polis&Winemiller, 1996;Brussaard,
1998).Theexamplesofassemblages from theliteraturewerefollowed ifpossible(e.g.
Brussaard etal, 1997;Brussaard, 1998;White, 1974).Sometaxamaybelongtomorethan
onefunctional groupbecauseofshifts intheirlifehistorytraits.
Thebiomassofthetrophospeciesreflects their ecological functions (Ryszkowski etal.,
1993);biomass estimations aretherefore appliedtoillustratetherelative importance ofgroups
andinteractions inatwo-dimensional diagram ofafarm food web.Rough estimations,ina
tenfold orderofmagnitude,werebased ontheavailable literature,preferably withdata from
organic farms inFlevoland, organic farms ingeneral (e.g. Kromp &Meindl, 1997)or
unsprayed crop edges(e.g. Boatman etal.,1999).Themeanbiomassofarthropod taxa
observedby Schekkerman(1997)wasusedtorelatedensity datatobiomass.Relative
importancewas assessed toderiveafoodwebdiagramfromthemorecomplex food web
matrix.Thefarm food webdiagramwasdrawninafashion similartothe food webdiagrams
ofOksanene/a/. (1996).
2.3.Relatingthefarmfood webtofarmmanagement
Therelationshipbetween food web structure and farm management wasexploredby
comparing four management typesoforganic arablefarms inFlevoland: short organic
durationwithoutimproved ecologicalinfrastructure (E.I.),shortorganicdurationwith
improved E.I.,longorganic durationwithout improved E.I., andlongorganic durationwith
improved E.I.Thesefourbasicfarmtypeswereconsideredtorepresenttheextremesoftwo
different gradients (cf.HoltinPolis&Winemiller, 1996)withregard toduration oforganic
farming practice andqualityoftheecological infrastructure. Inaddition, adistinctionwas
madebetween longduration farms withimproved E.I.with extensive and littleherbivory in
thecroparea.Thus intotalfivefood webswere constructed.
Organic farming durationwaspresumed torelatetothe amount ofinputoforganicmatterin
thecropareasoil.Thisinputincludesorganicmanure,compost andcropresidues ofin
particular,thegramineous crops(leypastureand cereals).Additionally,organicdurationalso
relatestoanincrease ofthecropdiversity aswellastheweed diversity.Theeffects ofbothan
increased inputoforganicmatter and crop/weeddiversitymay accumulateoveryears(Hald
&Reddersen, 1990;Idinger &Kromp, 1997).
Thequality('improvement') oftheecological infrastructure relatesparticularly tovegetation
structure anddiversitywithintheboundary, and islargely determinedbythemowingregime.
Mowingwith afinger-bar mower after June 21st, seemstobeoptimal for arthropod
abundance anddiversity inFlevoland,whencompared tothetraditionalmanagement ofmore
frequent mowingwithaflail mower(Smedingetal.,2001b).Inadditiontothevegetation
features, E.I.qualityrelatestothedimensions offield margins and consequently tothe
proportionofsemi-natural habitat onthetotal farm area.
Performances of farm food web structures ofthe four theoretical farms werederivedby
roughlyrelatingthe available detritusandplantresourcestotheabundance ofdetritivore and
herbivore functional groups,respectively. Anabundance offunctional groups atthehigher
trophiclevelwasassumedtobeprimarilydeterminedbypreyabundance ('bottom-up').
However'topdown'control andhorizontal effects (i.e.competition) werealso considered,
withreference totheevidenceinliterature(Wiseetal.,1999;Tscharntke, 1997;Poweretal.,
1996;Booij &DenNijs, 1996).Analogous totheapproachofFretwell (1977),whocoined
thetheoryonpredator andresource limitation,the four presented hypothetical food web
structureswerebasedonexpertjudgementwithreference totheory from literature and
empirical data.
3. Results
Theresults sectionincludesthreeparts:
- anoutlineofthetopological foodweb;
- consideration ofthe effect of farm management onthe food web structure (i.e.relative
abundanceoffunctional groupsandstrengthoftheirinteractions);
87
anillustration ofthepredictionswith empirical datafromarable farms in Flevoland.
3.1. Topologicalfarmfood webonorganicarablefarms inFlevoland
Becauseoffrequently occurring omnivoryandintraguildpredation,trophiclevelsare difficult
toassessinthefarm food web.Itistherefore convenient tomakeabroad distinction among
four aggregate subsystems (Table1):
- aprimaryguildofherbivores;
- aprimaryguildofdetritivores;
- anintermediatelevelofmacrofaunapredatorsofinvertebrates;
- atoplevelofpredatorsofvertebrates.
Thecomposition ofthesefour aggregate subsystems isdiscussedbelow, andalsosome
remarkswillbemadewithregardtotherelativesizeandtheextentoftheenergy flow
throughtheherbivore anddetritivorebased food chains.
Table1
Thefood webmatrix of thefarmfood webonanorganic arablefarm inFlevoland (TheNetherlands); inrows
are theresources andpreyfunctional groups respectively, incolumns are thedetritivores, grazers and
predators, as represented by thesamefunctional groups; I = interaction and 2 =strong interaction (according
toboth observations and the literature references). Thelinesrepresent theseparate resources and thefour
aggregate subsystems (detritivores, herbivores,predators of invertebrates and thetop predators).
Subsystem
1 primary prod.
2 primary prod.
3 primary prod.
4 primary prod.
5 detritus
6 detritus
7 detritivores
8 detritivores
9 detritivores
10 herbivores
11 herbivores
12 herbivores
13 herbivores
14 herbivores
15 herbivores
16 predators
17 predators
18 predators
19 predators
20 predators
21 predators
22 predators
23 toppredators
Resource or functional groups
roots
leafs and stems
flowers of dicots
seeds
crop-residues, litter (C/N high)
slurry, stable dung (C/N low)
earthworms
microbivore predators
detritivorous arthopods
rootherbivorous arthropods
invertebr. flushfeeders (r)
invertebr. senescence feeders (K)
specialist anthophiles
granivorous arthropods
herbivorous vertebrates
epigeicpredacious beetles
wandering andweb spiders
vegetation dwelling arthropods
parasitoids
soil-life feeding vertebrates
insecti-granivorous birds
specialist insectivorous birds
raptors,mustelids, opportunists
7
1
2
2
8
1
2
9
10 11
1 2
1 2
1 1
1 1
2
1
1
16 17 18 19 20
12 13 14 15
21 22 23
1
1 2
2
1 2
1
1
2 2
2
1
2
2
1
1
1
X
X
X
X
X
X
X
2 1
1
1 1
2 2
2
2
1
1 1
1 1
2 2
1 1
1 2
1 2
1 1
X
1
2
1
2
1
1
1
X
1
X
1
X
1 1
1 1
X
1
X
1
1
2
1
1
1
2
1
X
X
X
1
2
1
1
1
1
X
3.1.1.Herbivoresubwebprimaryguilds
Guildscanbeassembled accordingtotheexploited partoftheplant:roots,greenmaterial
(leafs and stems),flowers and seeds(DeSnoo&Canters, 1988;Crawley, 1983)(Table1).
88
Therootherbivorous guildbelongstothesoilbiota(Brussaard, 1998)anditmainly includes
herbivorous nematodes,mitesand insect larvae.Nematodes maydeterminethe amountof
rootherbivory onfarms (Wardleetal, 1999).Howevernematodes andmites aresomuch
interlinked withthemicropredator food web(presented below)thatweconsidered themasa
component ofthat assemblage.Rootherbivorous arthropods inarable agroecosytemsare
mostlypolyphagous larvaeofDiptera, Coleoptera andLepidoptera. Their food alsoincludes
seedsand seedlings(Gangeetal, 1991)(Table 1).Feedingondetritusmay alsobe significant
insometaxa(Strongetal, 1996).Theroot-herbivore guildbiomass(Table2)inthe farm
food webisgenerally largerthanthebiomassofalltheaboveground herbivores (Tscharntke
&Greiler, 1995;Wardleetal, 1999),particularly when leatherjackets (Tipulaspp.)are
enhancedbygramineouscrops.
Table2
Estimates of thebiomass magnitudes (kgdry weightper ha)offunctional groups at organic arablefarms in
Flevoland;theestimates are average values withregard toafarm of around 40hawith 5% ecological
infrastructure and 30%gramineous crops. Sources: (a) Van derBurgt, 1998; (b)De Ruiter etal, 1993,1995;
(c)Kromp &Meindl, 1997;(d)Schekkerman, 1997;(e)Smedingetal, 2001b; (f)Buys etal, 1996;(g)Hospers,
1991; (h)Booij, oral communication; (i)Remmelzwaal & Voslamber,1996; (k)Lange etal., 1994;(m)Smeding
& Booij, 2001.
Functional group
earthworms
microbivore predators
detritivorous arthopods
root herbivorous arthropods
flushfeeding folivores
senescense-feeding folivores
specialist anthophiles
granivorous arthropods
herbivorous vertebrates
epigeic predators
oligophagous predators
parasitoids
soil life-feeding vertebrates
insectivorous birds
top predators
Range of
biomass
10
1000
0.1 1
0.1 10
1
100
1
100
0.1 10
0.001 0.01
0.01 1
0.01 0.1
0.1 10
0.01 1
0.001 0.01
0.01 0.1
0.001 0.1
0.001 0.01
Reference
a
b
c
d
c
c,e
f,g
h
i,k
c,h
c,e
e
i,m
i,m
i
Folivores canbesubdivided intotwoinvertebrate assemblages(Table 1):flush and
senescence feeding folivores. Theflush feeding folivores (White, 1978) feed onyoungtissues
with lowC/Nratio and lowfibrecontent. Thecharacteristic modesof feeding areusually
sucking,boring andmining (Crawly, 1983).Theyhave asmallbodysize,afast development
andgood dispersal abilities. Senescence feeders feed onmatureplanttissues. Originally
White (1978)had defined this group as feeding ontissuesthathaveincreased nitrogen levels
causedby stress orageing. Inthis articlewealsoinclude folivores which feed onpresumably
healthymaturetissueswhich couldhave ahigh C/Nratio.Characteristic modes offeeding are
clipping,holingorremoval (Crawly, 1983).Senescence feeders tendtohaveaslower
development oralargerbody size(Crawley, 1983)andpossess,related toamore sedentary
behaviour, defensive traitstopredation (Poweretal, 1996).Theflush feeders largely
determine thebiomassofthe folivorous guildsonthe farm; andtheir exponential increase,
dependant onhowsusceptiblethecropis,andonweather conditions,may temporarily
determinetheaboveground herbivore biomassonthe farm.
89
Theanthophiles guild(Kevan, 1999)involvesinsectswhich aredependant on flowers intheir
entirelifecycle(specialists) oronly intheadult stage(non-specialists). The former are
particularlybees,either solitary (Tscharntke etal, 1998)orsocial(Svensson etal, 2000).
Thelatterareinsectswhoselarvaecanbeherbivorous (e.g. butterflies andmoths),predacious
(e.g.syrphid flies, cantharidbeetles),parasitoids,ordetritivorous (e.g. anthomyid flies).
Specialist anthophilebiomass,which, inFlevoland, mainlyconsistsofbumblebees,issmallin
comparisonwiththebiomassofotherherbivorous guilds(Table2).
Theaboveground granivores guild involvesinsects,birds andmammals.Becauseofthe
difference intheirlife history,vertebrates areplaced inother functional groups.The
granivorous invertebrate functional groupincludethecarabidbeetlegeneraAmaraand
Harpaluswhicharenotoriousgranivorous (aswellasbeingomnivorous);and other
granivorous insectslikeweevils andlygeidbugswhicharemainlyoligophagous (Westerman,
inprep.).
Herbivorous vertebrates onthe farm mainlyinvolverodentsand afewbird species(e.g.
pigeon andhouse sparrow).Theirlargebody sizeanddigestive capabilities allowthemto
feed onawiderangeofplanttissues.Thediet offor examplethewoodmouse,anabundant
speciesinFlevoland field margins,alsoincludes animalfood (invertebrates,bird eggs)
(Langeetal, 1994).Seedsareanimportant component inmixed dietsbecause oftheirhigh
nutritionalvalue.
3.1.2. Detritalsubwebprimaryguilds
Thedetrital food webcanbedivided intothreemajor divisions (Brussaard etal, 1997;
Brussaard, 1998;Wardleetal.1999):themicropredator food web,saprovorous arthropods
andthesoilengineers (i.e.earthworms).
Themicropredator food webisinfact acomplex system initself(DeRuiteretal, 1993,
1996;Brussaard, 1998)comprisingbacteria-based and fungi-based compartments.Primary
consumersaremicrofauna likeprotozoa andnematodes;topspecies are micropredators
comprised ofmesofauna mites(Acari) andspringtails (Collembola).Because ofrespiration
lossesbyseveralprecedingtransfers, thebiomassofmicropredators isrelatively small
(Table2).
Thesaprovorous arthropod guildinvolvesmeso-andmacrofauna which feed directlyonplant
debris andonmicroflora whichdevelopsondecayingtissues.Largespringtails, Diptera
larvae (e.g. Chironomidae, Sciaridae) and staphylinidbeetleadultsand larvae areimportant
groups(Sinnigeetal, 1992;Weberetal, 1997;Frouz, 1999;Bohac, 1999).Taxonomic
composition ofthisguild isaffected bysubstrate quality,for examplethenitrogen(Bohac,
1999)andsugarcontent (Weberetal, 1997).
Theengineersguild (Brussaard, 1998),althoughprincipally saprophagous, eatsbulk-soil
whichmayalsoincludeotherkindsoffood (microflora, seeds).Themajor characteristic of
thisguild istheircapability ofsoildisturbance.Although earthwormsplay aminor direct role
insoilmetabolism,theirbiomassmaypredominatethetotalbiomass ofdetritivorousmesoandmacrofauna inarablefields(Table2).
Insemi-naturalhabitatswith apermanent litterlayer,itmightbeconvenient to distinguish
withinthesaprovorous guild,anepigeicdetritivore functional groupthatinvolvesin
particularwoodlice (Paoletti &Hassal, 1999),diplopods (Sinnige etal, 1992),slugsand
snails.Thisgroup alsoexhibitstransitionsfromherbivoroustodetritivorous traits,for
exampleabundant slugsfeeding onsowthistlesthathadbeenweeded outofthe croparea,
90
andplaced inthecropedge(Smeding,unpublished data).Forreasonsofsimplicity,this
articledoesnot distinguishthisgroup.
3.1.3.Predatorguilds
Sixdistinctivepredatorfunctional groupsorguildsrepresent ashift inemphasis from
detritivoretoherbivore subweb:
- Epigeicpredaciousbeetlesincludingpolyphagouscarabidandstaphylinidbeetles;
- Spiders,bothwandering andweb-building spiders,that areground and facultatively
vegetation dwellingpolyphagouspredators;
- Vegetation dwelling arthropodpredators includingpolyphagous species (e.g.cantharid
beetles,myridbugs) andoligophagous species.Oligophagous speciesincrops are often
aphidophagous (e.g. ladybirds,syrphid flies)butnotalwaysso,for examplepredacious
Diptera(e.g. Empididae,Dolichopodidae) which feed onsmallDiptera andHymenoptera;
- Parasitoids (mainlyHymenoptera)whichdonotonlyexploit,asisoften thought,aphids
andlepidopteransbut also,for example,detritivorous Diptera (Potts &Vickerman, 1974)
orspiders (Topping &Sunderland, 1996);
- Insectivorousbirds including twofunctional groups:specialist insectivores thatare
capableofcatching flying insects;insecti-granivorous specieswhichconcentrateon
feeding amongthevegetationoninvertebrates andseeds;
- Soil life-feeding vertebrates,includingbirds(e.g. lapwing and starling) andmammals
(e.g.moleandshrew).
Forreasons ofsimplicity itisconvenient tocombinethepredacious beetles and spidersina
guildof'epigeic polyphagouspredators'(e.g. Poehling inBooij &DenNijs, 1996).The
epigeicpredatorshaveakeyposition inthefarm food web,inthatthey exploitboththe
herbivore andthedetrital subweb(Sunderlandetal, 1996;Kromp, 1999;Wiseetal, 1999).
Soalthoughtheybasically depend onthe abundanceofthesoilmesofauna, e.g. springtails
(Potts&Vickermann, 1974;Holland &Thomas, 1997)theyalsotemporarily exploitthe
increased herbivorepopulation inthesummer(Wiseetal, 1999;Schoenlyetal, 1996),and
somightprevent outbreaks ofr-herbivores ifthesepopulationsbuild up slowly(Burn, 1988).
Insectivorousbirds alsoexploitbothsubwebsbut arelessnumerous,comparedtotheother
predator groups.Compared tootherpredacious groups,epigeicpredators may achievethe
highestbiomassinarablefarm food webs(Table2).
Intraguildpredation, includinghyperparasitismandcannibalismprobably stronglyaffects the
abundanceofindividualpredator guilds(e.g. Tscharntke, 1997;Sunderland etal, 1996).
Examples arethepredation ofalreadyparasitised aphidsbyvegetation dwellingpredators,
carabidbeetles feeding onspiders,orinsectivorousbirds feeding onadult syrphid flies.Birds
probably consumerelatively morearthropodpredatorsthanprimary invertebrates when
comparedtotherelativeabundanceofthesepreyspecies,becausetheymayprefer larger
individuals. Since epigeicpredatorscanhideunderthesoil surface orhavenocturnal
behaviour (carabid beetles),vegetation dwelling arthropods areanimportant prey forbirdson
arable farms.
Haematophagous (bloodfeeding,parasitic)andscatophagous (dungfeeding) insectsand
scavengers aresmall functional groups(e.g. Potts&Vickermann, 1974;Weberetal, 1997)
thatexhibittransitionsfrompredacioustodetritivorous traits.Thisguildwhich feeds onthe
produceofvertebrates maycontribute significantly tothepreyofinsectivorousbirds (e.g. the
swallow).Thiscould occurwherecattlearetemporarily grazing onleypasture orinthe
stable,orwhendungisstoredon farm headlands (Hald&Reddersen, 1990;Smeding,
unpublished data).Forreasonsofsimplicity wearenotconsideringthese functional groups.
91
3.1.4.Thetoppredatorguild
Toppredators arethevertebrateswhich aretruecarnivores(e.g. kestrel,barnowl,weasel,
stoat)oropportunistic omnivores(e.g. carrioncrow).Theircommoncharacteristicisthe
abilitytopreyonothervertebrates andtheirpreference forpreyofalarger size.Sometop
predators,whichvisitthe farmbychance,belongtothefood web attheregionor landscape
level(e.g. henharrier,blueheron,andgulls).Theabundance ofherbivorous vertebrates
stronglydeterminestheresource availability for thetruecarnivores (Plesnik &Dusik, 1994).
ThebreedingdensityofkestrelsinOostelijk Flevoland, intheyears following reclamation,
relatedpositively totheirfood supplywhichwasmainlycommonvoles.However, nestling
mortality wasnot affected byadecreased voleabundance asthenestlings could alsobe fed
withchicks,inparticularthoseofstarlings(Cave, 1968).
3.1.5.Therelativesizesofherbivoreanddetritivoresubsystems
Asinmostterrestrial ecosystems,thefarm foodweb consistsofaherbivore subweb anda
detrital subweb(Odum, 1973;Polis&Winemiller, 1996).Food chains inthetotal farm food
webmay,bychance,achievealengthof9steps.Howeverthenumberoffunctional trophic
levels(Poweretal, 1996)ismuch less,presumably approximating thecommonchain length
of4(Winemiller &Polis,1996).
Inagroecosystems thedetrital subwebisexpected tobemuch largerthan theherbivore
subweb intermsofbiomass andspeciesdiversity (Wardleetal, 1999; Swift &Anderson,
1993).Thiscouldbeexplained from theviewpoint ofresourceavailability.Inmostnatural
systems,onaverage,about 10%ofnetprimaryproduction(NPP)isgenerallytakenby
herbivoresandabout90%bydecomposers; insectherbivores consumeusually lessthan 1%
ofNPP,whereasruminants caneasily assimilatemorethan 10%(Crawly, 1983;Edwards&
Wratten, 1980).Onarablefarms theaverageherbivoreconsumption might alsobelessthan
1%becauseharvestingremoves alargeproportion ofNPPandherbivory isinhibited byboth
thedirect andindirect measuresofthe farmer. However evenasmallamount ofconsumption
maycausegreatdamagetotheplant (Tscharntke &Greiler, 1995;Crawly, 1983)and
therefore involvelargeeconomicloss.
Incontrasttotheherbivore subweb,thedetrital webreceives extra food intermsoforganic
manure,organicwastes andcropresiduesofboth allochthonous and autochthonous origin.
However 90-95%ofenergyindetritusisusedbytherespiration ofsoilmicro organisms
(Swift &Anderson, 1993).Consequentlythebiomass ofthemesofauna (i.e.thetop
organisms ofthemicropredator food web)isamazingly small(DeRuiteretal, 1993,1995)
(Table2)comparedwith,for example,earthworms.Therelativedifference betweenthe
biomassofmacrofauna (i.e.largeinvertebrates) ofthedetritital subweb compared tothe
macrofauna oftheherbivore subwebmaytherefore notbeverymarked. Inotherwords:
althoughthesizeatthe food webbasemaydiffer extremelybetweenboth subwebs,the
quantitative difference seemstobemuchsmaller atahigher trophic level.Thissupposition is
supportedby studiesofRyszkowski etal. (1993)onthe aboveground insectbiomassin
several agricultural landscapes:herbivore subwebbiomass (including alsothe adultsofroot
herbivorous larvae)wasgenerally largerthanthebiomass ofinsectsoriginating from the
detritivore subweb.However, comprehensive dataonthissubject arescarceand couldbe
biasedbyseasonal andannual effects.
92
3.2.Farmfood webstructurerelatedtofarmmanagement
Inthetextbelow,thefivefood webstructures arepresented and illustratedwithfood web
diagrams.Firstly,attention isdrawntothecrop areacontributionstothe farm foodweb;
contrastingthe food webofashort organicduration farm and lowE.I.quality(typeA;Fig.
la),withthefood webofafarm with longorganicduration and lowE.I.quality(typeB;Fig.
lb).Nexttheeffect ofimprovedE.I.(i.e. withanincreased area andvegetationdiversity)on
the farm food webisconsideredbycontrastingtheabovetwomodelswithout improved E.I.
withshortandalongduration farmswithimprovedE.I.(typesCandD;Figs, lc and Id).
3.2.1.Shortdurationfarm withoutimprovedE.I.
Thefarm food weboftypeA(Fig. la)represents arelatively smallandlowfood web
structure.Thefood web islargelydeterminedbythedetrital food web,however soilmesoandmacrofauna densities arelowwhencompared tothelongduration farms (typesBandD).
After theconversion toorganic farming herbivore densitiesincropsmay initiallyremain low.
However, cropsmaybecome susceptibletoherbivorybecausethefarm hastoadapttoa
changed fertility management andtheepigeicpolyphagouspredatorpressureisrelatively
weak.Incasesofunbalanced luxuriousdevelopment ofthecrop,herbivores, (including
senescencefeeding folivores, flush feeding folivores androotherbivores)mayrapidly
establish inthecropand inducetemporarilyhighvegetation dwellingpredatordensities.
Characteristics oftraditionallymanaged E.I.are:
- ahighabundance offoliar herbivores related totheprolonged vegetative development of
thegramineous sward;
- epigeicpredatorsthat areattractedbythewarmmicroclimate ofsparsevegetation;
- herbivores (e.g. granivores)relatedtoannualorruderalplantsindisturbed swards;
- specific detritivorous arthropod taxarelated torelatively easily decomposable cuttings.
Arthropod communities oftraditionallymanaged E.I.probably havelessinfluence onthecrop
areathanarthropodcommunitiesofimproved E.I.,becauseofamorerestricted food supply
(bothquantitative andqualitative), andconsequently lowerdensities aswell asareduced
varietyoffunctional groups.
Vertebratepredatorsmaybemainlybirds feeding onsoilorganisms(e.g. lapwing)and
foraging insectivorousbirds,exploiting accidentalherbivore outbreaks(e.g.swallows feeding
aboveinfested crops).Forinsectivorousbirdstraditionallymanaged E.I.mayoffer a useful
butlimitedquantityof food.
3.2.2. Longorganicdurationfarms withoutimprovedE.I.
Thefarm food weboftypeB(Fig. lb) compared totypeAischaracterised byanincreased
detrital webinthecrop area.Particularly densitiesofsaprovorous arthropods and earthworms
mightbe increased whenthisiscompared to short duration farms (e.g.Heimbach &Garbe,
1996;Idinger etal, 1997).Theincreaseofthesegroupsmay support, inparticular, epigeic
predator functional groupsbutalsosomevegetation dwellingpredators likeEmpididaethat
feed onsmallDiptera. Longduration organic farms mightpossess arelatively diverse
populationofpotentialcroppestsandweedherbivores,duetotheaccumulated effect of
increased crop andweed diversity (Hald&Reddersen, 1990;Moreby &Sotherton, 1997).
93
Toppredators
Epigeic
predators
1
Wv""
Oligophagous
predators
\
Parasitoids-
., -Vy
Earthworms
Microbivore
predators
Saprovorous
arthropods
Detritus
\
Flushfeeding
herbivores
Root
herbivores
Crop plants
Senescence
-feeding
herbivores
Weeds
Anthophiles
Granivores
Perennial plantsE.I.
Fig. la. Predictedfood webstructurefor anorganic arablefarm withshort organic duration, without an
improved ecological infrastructure. Thicklines indicateprobable cases ofstrong interactions. Continuousthin
linesrefer to interactions of intermediate strength. Dotted lines referto interactions of minor importance. Boxes
with thicklines indicate a relatively high quantitative importance of thefunctional group within thefarm food
web.
Toppredators
Soil lifefeeding
vertebrates
Fig. lb. Predictedfood webstructurefor anorganic arablefarm withlong organic duration, butwithout an
improved ecological infrastructure. Symbols as inFig. la.
94
Vertebrate
herbivores
However,therelationshipsbetween andwithinpredator andherbivoreguildsmay alternate
betweentwoextremetrophic structures.Figs. Id and le illustratethis alternation withregard
tothecropareaof farm typeD.Theextremesdependontherelative strengthofpredation
pressurebythepolyphagous epigeicpredators andthedegreeofpest susceptibility ofthecrop
(VanEmden, 1988),whichisrelated toweather, soilnutrients,soilorganicmatter levels
(Phelan, 1997)andinteractionbetweencropandintercrop/weeds (e.g. Theunissen, 1994):
- Ifepigeicpredator abundance isrelatively loworifcrops aresusceptible toherbivory,the
flush feeding herbivoresmaybecomeapest (Fig. lb).Herbivores support adiverse
predator systembecauseneither epigeicpredatorsnoroligophagouspredators are
dominant. This systemmaycontrolincreaseofsenescence-feeding herbivoresbutnot
outbreaksofthemorevigorous flush feeding herbivores (e.g. aphids).These situations
mayoccurmorefrequently inintensiveorganiccroprotations;
- Ifepigeicpredator abundanceishighorthecropnotsusceptible,then allherbivores and
connected epigeicpredatorsmight depressoligophagouspredatornumbers.Epigeic
predatornumbers areprobably limitedby food shortages(DenNijs etal, 1997;Booijet
al, 1997)andmaytherefore exertapotentiallyhighpredationpressureontheherbivore
subweb,aprinciple referred toas'allochthonous energy subsidyviamultichannel
omnivory'byWiseetal.(1999).Herbivoreshigher inthecropcanopymay experience
lesspredation pressure (Kromp, 1999)andmightbepreyeduponmainlybyparasitoids.
Parasitoids maybereleased from interference byoligophagouspredators (cf.Tscharntke,
1997),orhavebetter abilitiestocopewith lowdensitiesofprey (cf.Powell &Nickless,
1996).This food web structure mayoccurmore frequently inextensiveorganic crop
rotationsduetolargedetritusresources andsparsercrops.
Withregardtovertebratepredators,increased densitiesmayoccur insoil life-feeding and
insectivorousbirdswhencompared to farm typeA.However, inparticular, the situationwith
increasedherbivory inthecropareamaysupport insectivorousbirds,becauseherbivores are
anessentialcomponent ofnestling diets(Poulsen etal, 1998;Hald&Reddersen, 1990),
whereasthenumerous epigeicpreyitemsarehiddenbynocturnalbehaviour (Vickerman&
Sunderland, 1974),or shelteredbyphysical structuresorprotectedbylowpalatability(e.g.
toohard for thechickstoeat).Therefore thefunctional food chain lengthofthefarm food
webmayget shorterwhen epigeicpredatorspredominate anddepresstheherbivore subweb,
andreducefood availability for insectivorousbirds.Accordingly,Poweretal.(1996)
hypothesised that food chainsmay shorten inasuccession from thepioneer stagetoan
established community duetotheincreasingly armoured features of sedentary taxaatthe2nd
or3rdtrophiclevel.
Herbivorousbirdandmammalnumbersmay alsobesupportedby anincreased seed
availability ofweeds andcerealsonlongduration farms. Asmalltop-predation layermay
subsequentlybebasedonanincreaseofherbivorous andinsectivorousvertebrateabundance.
3.2.3.Shortdurationfarms withimprovedE.I.
Thefarm food webofashortduration farm with animproved E.I. (TypeC;Fig. lc)will
combinetherelatively smallfood webinthecroparea(occurringonfarmtypeA)withan
increased andmore functionally diverse food webinthe field margins.Theresulting food
webstructuremaybecomeextended andmore satiated.
Theeffect ofimprovedE.I.onthe farm foodwebstructureismost significant withregardto
resources andconnected functional groupsthat arelackingor scarceinthecrop area: flowers,
seeds,anthophiles, granivores andsenescence feeding herbivores. Specific taxaof
detritivorous arthropods aresupportedbythevarietyoflittertypes.Both increased arthropod
numbers,aswellasvariedvegetation structure, supportvegetationdwellingpredators.
95
Primary functional groups andinvertebratepredatorsmaydispersefromthe E.I. intothecrop
(Sotherton, 1994, 1995; Lys&Nentwig, 1992).
Vertebrate functional groupsincludespeciesthatbypreference resideintheE.I.,feeding on
thelocallypresent seedsand arthropodsbutprobably alsoonimported flying insectsthat
adheretotallvegetation.
3.2.4. Longdurationfarm withimprovedE.I.
Improved E.I.probably addssimilarresourcestothefood webofalongduration farm (Type
D;Fig. Id)astothefood webofashortdurationfarm (TypeC;Fig. lc).However,onalong
duration farm theaddition ofherbivore subweb functional groupsmay further satiatethe food
webstructure andcausecumulative effects. Thegreatertheamount andvarietyofresources
could,for example,giveabetterabsorptionbythefood weboffluctuations orinterruptionsin
thefood supply,duetooperations inthecroparea.Inparticular,populationsoflargemobile
arthropod predators,insectivorous birdsandtoppredatorsmightbesupported and stabilised
byimproved E.I.Foodwebsoffarms including somedegreeofherbivoryoncropsandweeds
(Fig. le), arelikelytosupport moreinsectivorous birdsandtoppredators than farms with
depressedherbivore subwebsduetoabundantpolyphagouspredators orherbivore resistant
crops(Fig. Id)(asexplained inparagraph 3.2.2.).Incropareaswith littleherbivory,
insectivorousbirdsmayhavetodepend moreonimproved E.I.for highquality sourcesof
prey.
Soil lifefeeding
vertebrates
Earthworms
Microbivore
predators
Saprovorous
anhropods
Detrims
Crop plants
Weeds
Perennial plants E.I.
Fig. !c. Predictedfood webstructurefor anorganic arablefarm withshort organic duration including an
improved ecological infrastructure. Symbols as inFig. la.
96
Soil lifefeeding
vertebrates
Crop plants
Weeds
Perennial plants E.I.
Fig. Id.Predictedfood webstructure affected by increased detritalsubsidy,for anorganic arablefarm with
long organic duration including an improved ecological infrastructure. Thefood webstructure expresses the
indirectlyinhibiting effect of detritalsubsidy onthe herbivore subsystem. Symbols as inFig. la.
Toppredators
Soillifefeeding
vertebrates
Cropplants
Weeds
Perennial plants E.I.
Fig. le. Predictedfood web structure affected byan r-herbivoreoutbreak,for an organic arablefarm with long
organic duration including an improved ecological infrastructure. Thefood webstructure expresses the 'bottom
up' effect of increased herbivorousprey availability. Symbols asinFig. la.
97
3.3.Supportfrom empiricalresearch onorganicarablefarms in Flevoland
Resultsfromempiricalresearchonarable farms inFlevoland givesomesupporting evidence
for themodelspresented above.Observations ofthe four farm types showed:
- shortorganicduration farms (typeAandC)had inthecrop arealowdensitiesofallthe
functional groupsofvegetation dwelling arthropods or,inmoredenseluxurious crops,high
densitiesofsenescence feeding folivores associated withincreased predator abundance
(Smeding etal.,2001b).Bird densitiesonthese farms were low compared tootherfarm types
(Smeding &Booij,2001);
- longorganicduration farms (typeBandD)hadinthecrop areatwo distinctive
compositions ofvegetation dwelling arthropods:onewith abundant flush feeding folivores
related tointensivecroprotation, andanotherwithmoderately abundant detritivores and
parasitoidsrelated toextensive croprotation(Smeding etal.,2001b).Accordingly epigeic
arthropodshad alowabundance inlongduration farms withintensive croprotation (Smeding
etal.,2001a)ascompared tofarms with alessintensivevegetableproduction. However,
evidence for increased epigeicpredator abundanceonlongduration organic farms with ahigh
proportion ofgramineous crops,wasnot found, becausethesewerenotwell represented in
the studyarea;
- longduration and improved E.I. farms (typeD),includingmainly intensive vegetable
producing farms, hadthehighest territorydensitiesofinsectivorous birds,probably relatedto
bothE.I.andcropcharacteristics (Smeding &Booij, 2001).Insectivorousbird abundance
seemedtobenegatively correlated tomoreextensive croprotations;
-improved E.I.borderedbylargeconventionally managed cropplots (resembling type C)had
highdensitiesofinsectivorousbirdterritories andsupported alsoherbivorous mammals
(Remmelzwaal&Voslamber, 1996).
4.Discussion
4.1. Onthevalidation ofthemodel
Inthis articleweproposed atopological farm food web(basedonthe farm food webof
organic arable farms inFlevoland, TheNetherlands) andrelated this food webtotwo
important farm traits:theduration oforganic farming andthe amount of ecological
infrastructure. Thisexerciseledtothedistinction offourbasic food web structures.An
additional subdivision couldbemadebasedonthe levelofcropherbivory in long-duration
organic farms. Itmightbeclearthat theoutlinedresponses ofthefarm food webto farm
management werebased onamixof field evidence,theory andinterpretation. Theabove
presented empirical dataillustrate thefood webbut areprincipally not applicable as
validation,becausethetheorywaspartlyinspired bythesamedata.Furtherresearch is
required tovalidate ourmodel food webs.However, wethinkthatthe ideasthat havebeen
presented, despitetheweaknesses intheirvalidation,providevaluable hypothesesand
incentives for further research.
4.2. Integration ofecosystem servicesandnature conservation
Thedurationoforganic farming aswell astheamountofecological infrastructure affect the
farm food web.Bothvariables areuseful for implementing theintegration of ecosystem
services(Altieri, 1999)andnatureconservation-centred aims.However, the effect ofduration
doesnotalwayscoincidewiththe effect ofamoreextensivecrop rotation (i.e.theproportion
ofgramineous cropinthecroprotation),sincecurrentorganicpractice could includevarious
98
degreesofintensity.Foodweb structuresmaydiffer significantly between extensiveand
intensive longduration organic farms; difference in'intensity' amongorganic farms involves
inputofC(particularly cropresidues andstrawinmanure) aswell asweedcontrolandcrop
performance duetonutrient availability.
Theresultsofthis article suggestthat food websthat supportbeneficials (i.e.thepolyphagous
epigeicpredators)maynotnecessarily supportconservation-worthy species like insectivorous
birds.Longdurationorganicfarmswithanintensivecropping systemaswellasanimproved
E.I. seemtocombinetogether,toareasonable degree,boththeaimsofecosystem services
andofnatureconservation. However, ifthesesystemsweretobeoptimised, theincreased
employment ofbeneficials mightruncountertonatureconservation aims.Anincreased
efficacy ofweed control inthefuture, might also further diminish the food resourcesinthe
organiccrop areaavailable for thesebirds.
Thepresented modelsofthe farm food web showedthepositive effect ofE.I.onnature
conservation aims.Thiseffect mayoccurrelatively independentlyfromorganicduration.It
must,however,benotedthat shortduration farms arenotthesameasconventional farms,
wherepesticide and fertiliser drift mighthappen (DeSnoo, 1995).Indirect effects ofE.I.on
'ecosystem services'inthecropareacouldbepresumedbutmaybelessevident thanthe
effects ofE.I.onconservation-worthy species atthe farm level.
4.3Recommendationsforresearch
Hypotheses of further researchmightconcentrate ontheeffects ofincreased detritus supplyin
the farm food web(e.g. Wiseetal, 1999),theimportance ofdetritivorous mesofauna for
epigeicpredators(e.g. Holland &Thomas, 1997;Idinger &Kromp, 1996)andtherelation
betweenherbivory andhighertrophic levelsofthe farm food web (e.g. Poulsen etal.,1998;
Tscharntke &Greiler, 1995).Applied researchbased onfood webmanagement, may address
themanagement ofcropresidues andothernon-harvestablecomponents (NHC)(Vandermeer
etal.,1998)aswellasthepossibilities forcontrolledherbivory inlivingmulches,leysetc.
(e.g.Theunissen, 1994, 1997).Itwouldbeworthwhiletolinkthefarm food webmodel,as
proposed inthis article,toafarming system model(e.g. Oomen&Habets, 1998;Wolfert et
al, 1997)whichcanbroadly estimatetheresource availability ofvariousdetritus andplant
tissuequalities,basedon farm managementtraits.
Finally, alsothespatial distribution ofresources for functional groups shouldbe addressed
(e.g. Topping, 1997;Kreuss &Tscharntke, 1994)aswellastheeffect ofphysical disturbance
andshelteronmortality (e.g. DenNijs etal, 1996)orbirdnesting success (e.g.Wilson et al,
1997).However,accordingtoauthorities infood webresearch(Polisetal, 1996),when
referring tothecurrent stateofknowledge,careisneeded sothat thecomplexfieldstudy
scenario isnot entangled withthemethodology usedbytheresearcher.
Acknowledgements
TheauthorswishtoexpresstheirthankstoWouter Joenje andKeesBooij for discussingthe
articleandsuggestingappropriatereferences andArienavanBruggen for commenting onthe
manuscript. Thework attheWageningen University isfunded bytheMinistry ofAgriculture,
NatureManagement andFisheries,Department of Science andKnowledge Dissemination.
99
Chapter 7: Farm-Nature Plan: landscape ecology based farm
planning
F.W. Smeding3&W. Joenjeb
"Department ofPlant Sciences, Biological Farming Systems group, Wageningen University, Wageningen,
TheNetherlands
b
Department ofPlant Sciences, Cropand WeedEcology group, Wageningen University, Wageningen,
TheNetherlands
Abstract
Aprocedure ispresented for restyling the lay-out and management of farms in order to increase the biodiversity
inthe agricultural landscape aswell asthe sustainability farming. Theprotocol for the development ofan onfarm nature management plan uses landscape ecology characteristics, localbiotic and abiotic data andpotential,
aswell asthe farming system data and farmer's personal interests. Itmay also enhance the farmer's interest and
understanding ofagroecological pattern andprocesses and amore conscious approach to elements ofnature on
the farm, whichmaybethe startingpoint inecologising agricultural practice.
1.Introduction
Theintegration ofnatureand farming isanimportant issueinscientific aswell aspolitical
circles ofindustrialized European countries,inthe first place,populations ofmanyplantand
animalspecies associatedwithagriculturallandaredeclining inmany Western European
countries.Changes inagricultural land-use areoften suggested asthemaincauseofthis
decline (e.g. Wilsonetal, 1997;Fuller etal, 1995;Andreasen etal, 1996).These changes
haveconcomitantly had aneffect atthe landscape-level, resulting inalossof landscape
differentiation inEurope (Baldocketal, 1993).
AttheIUCNconference 1992onbiodiversity inRio deJaneiro,most European governments
committedthemselves toimplementing biodiversity conservation measures.InThe
Netherlands,thesecommitments arenowbeingtranslated intodeeds.Agriculture,the landuseaccounting for about 50%ofthecountry'sarea,isnot excluded from theseefforts to
conservebiodiversity, sincetheoccurrence ofmany species andcommunities isrelatedto
farmland and farming practices.
Apart from itsintrinsic value,biodiversity hasafunction inanumber ofecologicalprocesses
highlyrelevant for food production. These'life support functions' ofbiodiversity include for
examplethesoilnutrient cycles(Brussaard, 1997)andregulation ofpestsbymeansof
biological control (Altieri, 1994).Agro-technology hasbroadly increased theindependence of
these functions atthecostofhigh inputsof fossil fuel, artificial fertilizers andpesticides.The
concept of'sustainable' agriculture aimstore-establish anequilibrium: life support functions
andtechnology shouldbe farm attributes ofequalimportance.Here,theintegration of
farming andnaturecomesintoplay.
Frombothperspectives -theintrinsic and functional valueofbiodiversity in agriculturethereisastrongneedtodevelop farming systemsthatincludebiodiversity (Almekinderset
al, 1995;Vandermeeretal, 1998).These ideasareparticularly manifest inthecurrent
practice oforganic farming (EEC, 1994).Thestandards for organic farming guarantee safer
conditions forbiodiversity development bybanningtheapplication ofpesticides and artificial
101
fertilizer application andbyencouraging longcroprotation andmoderate stockingrates.
Nevertheless,organic farms also lack aclearperspective when itcomestointegrating nature
onthe farm.
Inthisarticle,wearguethatthe integration offarming andnatureinthecontext ofa
sustainable agriculture (including themanagement andconservation ofbiodiversity),should
comprisetwolevels:thelandscape level(100-1000ha)andthefarm level(10-100ha)
(Table 1).Asregardsthelandscape level,there shouldbecoherence,between the structureand
distribution ofthenon-productive (green)habitatsonthe farm andinthe surrounding
landscape.Thereason isthatconditions supporting biodiversity onthe farm are strongly
related toprocesses andstructures atthelandscape level.The first question therefore, is:what
aretheimplications ofthis landscape-level focus for farm-nature? Atthe farm level,these
greenhabitatsshouldbeclearly andpurposefully integratedwith farm management. Onlyif
habitat structures anddistribution arecompatible with(orbeneficial to)the agricultural
production, willtheybeabletosurvive and,asaresult,bioticcomplexity beabletoincrease.
Thesecondquestion tobeaddressed is:what doesthisfarm-level focus imply fornatureon
thefarm? Thethirdquestionisanextension oftheprecedingones:howcanthese
implications beworked out forreal farms,e.g. ina'Farm-NaturePlan'?How can farms
actuallybe're-styled' inordertoachieve abetter coherencewith landscapepatternsand
processesand abetter adjustment of farming tonature? Theoutlinesofaprocedure for such
anon-farm implementation willbepresented. Thisprotocol for aFarm-NaturePlanis
currentlybeingtested inDutch agriculturalpractice,mainlyonorganic farms, without
subsidiesonavoluntarybasis.
2.Farm inthe landscape
Thequestionofwhy this'coherence'between thegreenhabitat's structure anddistribution on
the farm and atthe landscape level issoimportant forthebiodiversity canonlybe approached
atlandscape ecology level andhastoinclude agroecosystem functioning.
Atthebeginning ofthiscentury,traditional farming wasbroadly inaccordancewith
landscape ecologycharacteristics andprocesses.Thetechnical and economicconstraintsto
farming weredirectlyrelated tolimiting natural resources andconditions.Crops,livestock,
tillageandmanuringhad aspatial distribution reflecting theprevailing abiotic conditions.
This land-usepatternresulted inagradient inuseintensity andproductivityfromthe farm
settlements onwards.Inadditiontothisspatially differentiated land-use,theuseofeach area
wasconsistently the sameovertheyears,i.e. constancy ofprocesses.Thistraditional land-use
resulted inahighbiodiversity (Westhoff etal, 1970;VanLeeuwen, 1966).However,
increasingly and especially since 1950improved technology andwelfare allowed agricultural
land-usetogain independence from natural resources andtheincreasing inputsof artificial
fertilizer andmechanisation have levelled outthehabitat variation.Nevertheless, modern
agricultural landscapes stillharbour abiotic andbioticdiversity. Thisvariation often refers to
vital ecologicalprocesses,particularly related totheeco-hydrology(Everts &DeVries,
1991).
Thedata from plant andanimal speciesinventories areextremely valuable. Because
vegetation succession and species immigration mostlytakedecadestobe accomplished (Van
Dorp, 1996;Hermy, 1994),itisdifficult toconclude thepotential suitability ofalocation for
certain species.Therefore, structures andprocesses atthesurrounding landscape levelhaveto
beused asreferences andresources forbiodiversity atthe farm level.
102
TableI
Important structures andprocesses (italics) on thelandscapeand thefarm levelsas related to ecosystem
components.
Component:
Landscape level (reference):
Climate
exposure to sun andwind, mesoclimate
Soil
soil type, inclination, soil/height transitions
{soil formation)
managing nutrient and organic matter
status, tillage, disturbance
Water
catchment area (river),water transport:
inundation, seepage, infiltration, leaching
or accumulation minerals, land-use
planning
ditches, drains,ponds, wells,water
management
Physical structures
(man-made)
Farm level(field ofoperation):
roads andbanks,dikes,urban zones,
construction
shade, shelter, erosion, deposition
buildings,tracks,fences, dumps/piles,
transports of matter, construction
Vegetation
present communities (including forest,
nature reserve),succession, population
dynamics, dispersal
pastures,arablecrops,weeds,vegetation of
linear habitats, dispersal, management and
control
Fauna
vertebrates andmigratory invertebrates,
migration,population dynamics
present species, domestic animals,
dispersal,population dynamics
Howcanpattern andprocess atthelandscape level(Table 1)be assessed inordertoachieve
suchcoherencebetween thehabitat infrastructure offarm andlandscape? Ifwe look atthe
landscape levelthere arethree ecological keynotestobe addressed:
- Similarity: thepromotion onthe farm ofplant andanimalpopulations already occurringin
theregion,mosteffectively enhancesthefarmbiodiversity. Semi-natural (green)habitat
types found inthesurrounding landscape couldbepresent orconstructed orreinstatedon
thefarm; afarm inanopen landscape couldhaveasolitarytreeorsomeshrubs,butis
better notplantedwithwoodlotsorhedges;
- Connectivity: ecologically related habitats (wet,wooded,herbaceous) shouldbeconnected
orbelocatedwithin acertaindistanceinordertoguarantee aminimumterritory size
withinthereachofdependent animal species (Opdametal.,1993);theon-farm green
habitats should linkupwiththehabitatnetwork present inthe surrounding landscape;
- Variationpotential: thevariation insoil andhydrological conditions atthe landscape level
aswell astheprocesses atwork onalandscape scale acting asagents for variation {e.g.
causinggroundwater seepagezones,flooding) shouldbeutilizedinplanninghabitat
arrangement andhabitat management atthefarm level.
Ifthesethreekeynotes areaddressed onanumber ofcontiguous farms,theircommon
landscape context will leadtocompatible greeninfrastructures thatwillpositively influence
eachotherandmayalsorestorecharacteristics ofthelandscape.Thissynergyorpositive
feedback mayhavethecharacter ofarestoration,but includes economically feasible farming.
Whenthethree landscape levelkeynotes areappliedtothe ecosystem components atthe farm
level,anumber ofrecommendations canbeidentified (Table2):
- Climate:general exposuretosunandwind,rainfall arethesamefor farm andlandscape;
103
Soil:different soiltypes andtransitionsmay extend intothe farm area,which couldbe
expressed bybotanical composition; thiscanbe enhanced by applying special
management onselected (promising) habitats (e.g. establishing grassy strips,removing
biomass after mowing);
Water:influx ofnutrient-rich orpolluted water from thesurrounding areamay strongly
influence on-farm habitat conditions;this shouldberestricted ifpossible;differences in
groundwater quality extending intothefarm areacouldbe expressed inthe local species
composition (Everts &DeVries, 1991);deepening ofaditch orconstruction ofapond
shouldbe linkedwiththe surface-water network;distancesuptoc.300menable
amphibians todisperse;
Vegetation:woody elements (hedgerows,woodlots,individual shrubsandtrees),canbe
planted toexpandthewoodynetwork orreinforce existingpatternsor isolated woody
elements inthe landscape;management ofwoody,dryorwet herbaceous vegetation
shouldrefer toexamples inthesurrounding areathat demonstrate subsequent
developmental stages and species-rich communities;
Fauna:measures for thepromotion ofcertain speciescould focus onresident (vulnerable)
species;toavoiddisturbance oflargespecies,particularlymeadowbirds,these efforts
couldbestbeatleast200mawayfrom settlements andmainroads.
3. On-farm nature
Theprevious sectionconsidered thecoherence inpattern andprocessbetween the farm and
landscape andrecommendations werederived forthefarm. Now,wewill emphasizepattern
andprocess atthe farm levelproper, including therelated activities andmanagement. The
challenge here istoestablish anexplicit linkbetweenthe farming measures and thedesired
developments infarm nature.
Anumber ofstructures andprocesses atthe farm levelcanbe important. Features atthe farm
levelaresummarized inTable 1.Howcanthesestructures andprocessesbeassessedand
addressed inaFarm-Nature Plan?Herewewill use four farm-ecology keynotes comparable
tothethreekeynotes atthe landscape level:
- Surfacearea: acertainpart ofthe farm areashould comprise green (i.e.semi-natural or
extensively managed)habitatsand serve asarefuge and asourceofvariation. Inanumber
ofcases anareaof5%ofthe farm hasbeenrecommended (Vereijken etal, 1994);
- Connectivity: similarhabitatsonthefarm (wet,woody,herbaceous) shouldbeconnected
orlocatedwithin acertaindistance inordertoensurethat dependent animal specieshave
atleasttheminimum territory sizeandcandisperse acrossthe farm (Opdametal, 1993);
- Variation: avariety ofhabitatsshould occuronthe farm; variation canbe addedwithin
thepredominant habitat typesbyapplying different management forms andthus
accommodating different plant species and animalsthate.g. requirevariation inpreyand
resources;thisholdstruefor generalistpredatorsofpestswhoneed'alternativeprey'when
pestpopulations arelow(Altieri, 1994).Variation alsorelatesdirectlyto biodiversity;
- Habitatquality: extensively managed habitats shouldbeprotected from manuring andsoil
disturbance inordertoallow communities ofoldersuccessional stagestodevelop;to
facilitate vegetation succession and small scaledifferentiation inecological gradients
there shouldbe asmuchcontinuity intheyear-to-year management aspossible, including
theuseofthefields(Westhoff etal, 1970);somevertebrate speciesrequire additional
measures tocompensate for orprotect against threats intheproduction area,e.g.
protection ofmeadowbird nests (Beintema, 1991).
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Table2
Developing aFarm-Nature Plan bytranslating ecological information (aboutstructures andprocesses) to
recommendations.
Component:
Landscape level recommendations:
Climate
utilize differences in microclimate
Soil
utilizerelief, soil-type, transitions
Water
correspond to flow patterns, seepage water
quality (i.e. thegeneral ecohydrology)
Physical structures
Farm level recommendations:
consider vicinity of roads and buildings
(disquiet)
Vegetation
reference communities under consistent
(nature) management; improve spatial
linkages ormaintain separation
Animals
reference communities, including species
with alarge home range
nutrient application inconsistentpatterns in
space and time;no input outside fields
manage water quality, quantity andlinks:
retention, rising water table, creating new
ponds and marshes
enable nesting and hiding of animals
creating and/or linking of similar habitats;
consistent management method ina
consistent distribution pattern; mowing
mainly withbiomass removal
facilities andprotection measures
Whenthe four farm-ecological keynotes areappliedtotheecosystem components atthe farm
level,anumberofrecommendations canbeidentified (Table2):
- Microclimate and climate:establishment ofsheltered and sunnyplaces;inopen
landscapes sheltercanbeprovided by shrubs,reed orevenhighperennial herbs;ditch
banksorpondswith asunny aspect should haveprioritywhen extraefforts aremadein
vegetation management;
- Soil and soil fertility: anymanuringoremission ofnutrients outsidetheproduction area
shouldbeavoided. Themargins ofpastures and,ifpossible,theedges ofarablecrops
could,therefore, receive lessmanure;difference infertility levels of fields shouldbe
emphasized; onmarginalfieldsonarable farms alessintensive croprotation canbe
considered;
- Farmbuildings:access andnesting facilities forbirds (swallow,barnowl) andmammals
(hedgehog, stoat)couldbe offered;
- Water:thepotential for conservingrelatively nutrient-poor groundwater andrainwateron
the farm shouldbeexploited; sometimesthedirection offlow canbechanged andthe
effects ofgoodwaterquality extended;thewaterlevel insomeditches couldberaisedby
damming.Ifthelandscapetypepermits,wet elements ordeeperwater canbe created;
- Vegetation: ifthelandscapepermitsnewlinearwoody elementsofatleast 3mwidthto
be established; theruleofthumbregarding themovement ofbirds,batsandbutterflies the
100meterbetween trees andshrubs;thepatternofwet,woodyandherbaceous elements
aroundfieldsshouldbeasinterconnected aspossible;agap shouldnever exceed200m
(radiusofaction for stoat and songbirds).Plots shouldpreferably benolargerthan 8ha.
There shouldbe arealistic andnottoocomplex annualplanning ofthevegetation
management ofverges andditchbanks,thatprovides for differences ingrowing stage
between orevenwithin linearelements;thereshouldbe aconsistent differentiation in
land-usepatterns,ifstocking ratepermits.
105
4. Protocol for aFarm-Nature Plan
Howcanorganicorotherfarms bemodified inordertoachievecoherence atthe landscape
level andintegrationofnatureatthe farm level?Theaboverecommendations werederived
from bothlevels.TheFarm-NaturePlanprotocol (Smeding, 1995)wasdeveloped forthis
purpose.Itisastepwiseprocedurethatleadstoamapofthe farm including site-specific
recommendations.
TheFarm-NaturePlanprotocol hasfivesteps:
- Theattunement: atalkwiththefarmer abouthisperception ofnatureonthefarm, his
wishes,technicalpossibilities andconstraints;
- Thesurvey: afieldvisitoftwodaystoidentify anddescribe allrelevant features resulting
in(1)a 1:5,000mapofthe farm, (2)a 1:25,000mapofthelandscape, (3) alistofthe
different habitat typesandtheirareasand(4)ashortreport onobservations ofhabitat
structure and composition; onlyconspicuous indicator speciesneedtobe identified;
information isalsocollected about land-useplanningpolicy andnature management
subsidiesrelevant for the farm;
- Theappraisal: anevaluation ofthefarm withregard to: (1)theareaof non-farmed
habitats,(2)theconnectedness ofsimilar (wet,woody ortallherbaceous) habitatsonand
aroundthe farm area,(3)thevariation and(4)qualityof farmed andnon-farmed habitats;
- Thechoiceofobjectives: adecisiononsite-specific andrealistic objectives for the farm;
thedecision isbasedonecological criteria(appraisal),the farmer's preferences and
management possibilities (attunement) and local land-usepolicy and subsidies (survey);
- Thedesign: starting from theobjectives andthe farm mapseveralpointsofattention are
checked;atthis stage,thelistofrecommendations (Table2)isconsulted to establish
landscape coherence andcompatibility with farming practices;theresult isamapofthe
farm areaincluding theexisting andplanned distribution ofgreen infrastructure, with
practicalrecommendations;particularly inthislaststepthe scientific/ecological
judgement istobecombined with creativity whenfindingalternatives for acceptable
solutions.
Bywayofanexample,letusconsider theFarm-NaturePlanmadefor theA.P.Minderhoudhoeveexperimental farm (Lantinga &Oomen, 1998),a89hamixedorganic farm inapolder
dominatedbyarableproduction. Theplan (Fig. 1)involved increasingthetotal areaofnonfarmed biotopes from 2.8to 5.8%.Foursowngrassybanksarecross-linking the herbaceous
network anddividing extended areasofarableland intoplotsof9haorless.
Themanagement intheditches isvaried,with theaimofachieving atallherb structure
(commonreed)and apoorlyproductivevegetation with increased flowering performance.
Thevegetation quality oftheditch slopesisguaranteed bymeansofagrassyfieldmarginand
anoverall mowing regimewithbiomassremoval.Theditchwithtallherbstogetherwith
shrubbycorners andanewlyplanted hedgerowhavetoprovide ashelternetwork for
insectivorous songbirds andsmallmammals likestoat andweasel.Additional measures are
takentoprotect and facilitate nesting ofswallow andblack-tailed Godwit.
Theprotocol wasdeveloped incollaboration withtheDutchNational Extension Service.The
procedurewastested in 1995atthreeorganic farms (Smeding, 1995).In 1996-1997
extensionistsmade27Farm-NaturePlans forDutch organic farms, ranging from dairyand
arabletofruit production, anddistributed overvariousregions intheNetherlands (Van
Almenkerk &VanKoesveld, 1997).In 199870%oftheinvolved farmers responded toa
questionnaire:40%ofthe farmers hadimplemented therecommendations and35%intended
todosointhe future. About 70%oftheinvolved farmers areusingtheFarm-Nature Planin
discussionswiththelocalgovernment,waterboards andnatureconservation authorities.
106
Fig. I. Farm-Nature Planfor theA.P. Minderhoudhoeve-WU experimental organicfarm (89ha), a,arablefield;
p, permanent pasture; s.farm buildings; c,canal; r,road withverge(s).Measures (width): I,grassbanks (3m);
2,ditch/common reed (5m);ditch rich inflowering herbs (5m);4,grassyfield margins (3m); 5,shrub corners
(25 m~);6,hedgerow (3m).
5. Discussion
Thedevelopment of fanning systemsthat includebiodiversity management isacomplex
topic.Theapproach presented inthisarticle emphasizes coherencebetween farm and
landscape features and integration ofnon-production habitat andfarm management. As
explained above,thisapproach issubsequently elaborated intoan advisory instrument
(protocol forFarm-NaturePlan)which assumesthatthe farmer willcollaborate and
participate actively.
Theapproach doesnotpretend tobefinalandcomprehensive;theFarm-NaturePlanprotocol
follows onlyoneparticular lineofreasoning,applying field experience and scientific
evidences mixedwithprofessional judgement. However, thecomplex system ofafarm can
alsobe approached from anotherperspective, for example,historical development, spatial
relationsor from different integration levels(crop,community,region).Certainly, more
scientific researchcouldalwaysbedonebefore givingpractical recommendations atthe farm
level.However, despite such criticism every alternative lineofplanning of farm-nature,
including theimplementation, tendstoposecomparableproblems.
107
Avaluablepointoftheapproachpresented isthewell-structured framework thatenablesopen
discussion and improvements.Theresultsofpractice-oriented scientific research canbe fitted
intothis framework, improving thecriteriaandguidelines. Important research topicsinclude:
the selection ofindicator-parameters atdifferent levels,food webson farms, dispersal
requirements for plantsandanimals,necessity ofplant species introduction, etc.
Afurther advantage isthattheprotocol istransparent andcanbe applied bynon-academics,
becausetheemphasisisonobservation of structures andgeneral characteristics of speciesand
vegetation.Last,butnot least:thefarmer's involvement indesigning aFarm-NaturePlanis
essential.Theresultsarestronglydependent onthe farmer's good intentions, understanding
andaccuracyintiming andpositioning ofactions.Theprotocol and Farm-NaturePlanseem
tobeeffective toolsinrestoring landscape and farming sustainability. Aswell ashavinga
high-tech context,precision farming (Rabbinge, 1997)may alsorefer toakeen understanding
anduseofecologicalpatterns andprocesses and atolerant attitude towardsnature elements
onthe farm: managingbiodiversity asthestartingpoint inecologising agriculture.
108
Chapter 8:General discussion
1.Observations andtheirimplicationsfrom afoodweb perspective
1.1. Empiricaldataonfood webstructures
1.1.1. Initialhypotheses
Itwasexpected thattheduration oforganicmanagement, anextensive croprotation andan
improvedecologicalinfrastructure (E.I.){i.e. enlargedarea,aregimeoflatemowing),would
relatepositively totheabundance ofnon-pest arthropod functional groups,includingprimary
levelsofthedetrital aswell astheherbivore subweb.Thecrop areawasexpected to support
inparticularthedetritivoresinthefarm food web,andtheE.I.wasexpectedto support
particularly the(K-)herbivore functional groupsthatmightbe scarceinthecrop area.An
increaseoftheprimary functional groupswould consequently enhanceinvertebrate predator
andparasitoidnumbersaswellasthenumbersofinsectivorousvertebrates(i.e.birds)that
feed onbothprimary andpredacious groups.Theincreased abundance ofthepredator
complex wasexpected toinhibit outbreaks ofpestherbivores.
1.1.2. Observations inthecroparea
Field studiesonorganic arable farms inFlevoland indicatedthat allthe factors included inthe
abovehypothesis, affected abundance and functional group composition ofboth arthropods
andbirds.However the effects differed from whatwas expected.
Inthecroparea(i.e.wheat crops),K-herbivore abundancewas associated with farms thathad
beenrecentlyconverted, whiler-herbivore abundancewasassociated with farms ofalonger
organicdurationwith anintensive croprotation.Bothobserved herbivore increasesmightbe
explained byacombination ofcrop susceptibility totheherbivoregroup and limitedpredation
pressure (Smeding etal, 2001b).Therewas,accordingtothehypothesis, some evidence
found for detritivore increase related totheextensive croprotations onlongduration farms
(Smeding etal, 2001b),andfor predator increases associated with detrital subwebonthe
moreextensive farms (Smeding etal, 2001a).Inthis lattercase,abroader definition of
'extensive'was applied, involvingboth croprotation and farming practices.Predator
abundance inthecropcanopywasparticularly relatedtohighK-herbivore numberson
recently converted farms; however thehighest speciesdiversitywasfound onlong duration
farms whichhad anintensivecroprotation(Smeding etal, 2001b).Thefarms whichhadan
extensive croprotation compared withtheother farms had alowpredatornumberinthecrop
canopy,whereastheparasitoidshad intermediate numbers.Thedensityofbirds' territories
seemedtobeenhanced bythecrop areasoflongduration organic farms with an intensive
croprotation. Thiswaspossibly relatedtoincreased herbivory (Smeding &Booij, 2001).
1.1.3.Observations intheecological infrastructure
Increased arthropod abundancewas found inthevegetation ofthe improved E.I. (Smedinget
al, 2001b).Theincreased functional groups includedbothpredators anddetritivores.
However K-herbivore numbersdidnotincreaseintheimproved E.I.whentheywere
compared tothetraditionally managed E.I.;perhapsbecausetheprolonged vegetative
development offrequently mownvegetation mightextendthe availability ofnutritive grass
tissue.Also,theabundance ofepigeicpredators,inparticular ofthequantitatively important
group ofpredacious beetles,wasnotrelatedtoanimproved E.I.(Smeding &Booij, 2001).
Observations suggestedthattheirnumberswererelatedtothecropareaconditions.Open,
frequently mown E.I.vegetation enhanced themore specific grounddwelling functional
109
groupscompared toimproved E.I.Theterritorial density ofinsectivorousbirdswaspositively
related tothehigh arthropod abundance intheE.I.(Smeding &Booij, 2001).
1.1.4. Observations ontheinteractions between theE.I. andthecroparea
Field studiesprovided noconvincing evidence for thedispersal of functional groups,
abundant intheE.I.,intothecrop area.Theeffects ofcropconditions onthe arthropod
functional groupabundance inthecropareaseemedtooffset theinfluence oftheE.I.
(Smeding etai, 2001b).Contrarytoexpectations,observations suggested theeffects were
reversed regardingepigeicpredaciousbeetles (Smedingetai, 2001a),and flying insectsthat
werepossibly transported intotheE.I.(Smeding etal, 2001b;Smeding &Booij, 2001).
Bird studiesrevealedpositivecorrelationbetweenbird functional groups and acombination
ofcropareaandE.I.characteristics (Smeding &Booij, 2001).Thismay suggestthatboththe
croparea andtheE.I.habitats areimportant tothesebirds.Thismay alsoholdtruefor birds
thattypically liveintheE.I.,becauseacertainproportion oftheirpreycould originate inthe
croparea.
1.2.Observations relatedtothefood web theory
1.2.1.Top downandbottomupdetermination ofabundance
Theinitial setofhypotheses wasbased onthegeneralisation that anincreased food webbase,
duetoanenlargedresource supply,relatestothe subsequently increased trophic layers
('bottom upcontrol',cf Oksanenetai, 1996).Ourfindings largelyconfirm theimportanceof
"bottomup'determination ondetritivores,K-herbivores,r-herbivores, invertebratepredators
andinsectivorousbirds.However,theplaceoftheresourceswasdifferent thanexpected: long
duration organic farms didnotprovide alarge food resourcetoK-herbivores and incaseofan
intensivecroprotation alsonottodetritivores.IntheE.I.,contrary to expectation
detritivorous arthropod numberswereenhanced bylatemowing andnotparticularly Kherbivorenumbers.
Additionaltoindications for 'bottom up'determination, indicationswere found for 'topdown'
effects {cf Wiseetai, 1999;Tscharntke, 1997;Poweretal, 1996).Observations ofboththe
K-andr-herbivore abundance suggested thattheexplanation ofherbivore abundancemight,
next totheherbivore susceptibility ofthecrop,also involveherbivore controlbypredators.
Anincreaseofpredationpressureonfarms, alonganintensity-gradient beginningwith
recently converted farms,may first depressK-herbivore numbers(onintensive farms oflong
duration)andthen alsothemorevigorousr-herbivores (onextensive farms oflongduration).
Thispresumedpredation pressure couldbeduetoepigeicpredators that are supported by
subsidised detrital food chains (Wiseetal, 1999;Polis&Hurd, 1996).Thepotential strength
ofsuchpressure issuggested byseveralreports onfood shortages for epigeicpredators
(Sunderland etai, 1996;Booij etal., 1996;Wiseetal, 1999).These'topdown' effects may
modify toacertain extentthegenerally 'bottom up'determined farm food web structure.
However,muchmoreresearchisrequired tofind conclusiveanswers.
Thepredominance ofaparticularpredator functional groupmay affect otherpredator groups
bymeansofpredation aswell ascompetition (e.g. Tscharntke, 1997).For example,an
abundance ofcarabidsorlinyphiid spidersmight affect syrphid fly larvae (oligophagous
predator) andparasitoids,which alsointeractwith eachother. Consequently parasitoid
distributionmighttoacertain extent,bedetermined bytheoccurrence ofpredators competing
with orpreying onparasitoids.Theseinteractions (i.e.'topdown'and 'horizontal effects' inthe
food web)defined as'predator interference' or'intraguild predation'may influence arthropod
110
functional group compositions.
Theabundanceofinsectivorousbirdsmightbenegatively affected bythe 'multi-channel'
omnivoryofepigeicpredators,sinceherbivores, especially K-herbivores arethe preferred
food items for insectivorousbirds(Poulsenetal, 1998).Thebirds feed, toacertainextent,on
ahigher trophic levelthan arthropodpredators;areduction ofbirddensitytherefore impliesa
shortening ofthe functional chainlength ofthe farm food web.Accordingly,Poweretal.
(1996)arguedthat food chain lengthwillget shorter inasuccession from thepioneer stageto
thesecondary stagebecausethegrazersorsecondary consumers possess armouredtraits
protectingagainstpredation. Thisviewpointwouldbethereverseofthecommonlyheldview
byecologiststhatthereisasuccession towards anincreased complexity.
Thehighestbirddensitieswereobserved on farms that combined intensive crop production
withimproved E.I.Thisobservation suggested, accordingtothehypothesis,thatthe
broadening ofthe food webbasemay facilitate ('bottom up1)highertrophic levels.The
negative indirect ('top down') effect ofdetrital subsidyonthe food availability tobirdsatthe
farm level,mightbecompensatedby food availability tobirds inotherhabitatsonthe farm
(e.g.inE.I.) and aroundthe farm.
1.3. ExtrapolationofFlevolandobservationstootherlandscapes
Thecomparative studyofarthropod communities andbirdsonfour organic arablefarms in
Flevoland andtheriverregion (Smeding &Booij, 1999;DenNijs etal., 1998)demonstrated
mainlycontrastsbetweenthelandscapes.Therelationofmost invertebrate functional groups
toE.I. seemedtobe ambiguous.However, the farm typewith increased E.I. ineach landscape
wasassociated withhighdensitiesofspecialist insectivorousbirds.
Observations suggested thatwheat crops intheriverregion compared towheatcropsin
Flevolandincluded amuchhigher speciesdiversity, involving for exampleanapparent
abundance anddiversity ofweeds.Abundant flowering weeds likecamomile, attracted large
numbersofanthophiles and also for example large-sizedpredacious Diptera(asilid flies) that
didnot occur inFlevoland; theterritoryofastonechat (Saxicola torquata) onfarm 'O-',an
insectivorousbird,andtheweed Venus'looking-glass (Legousiaspeculum-veneris) on farm
'O+'representedhighnatureconservation values (Smeding,unpublished data).Theobserved
increaseinspeciesrichness and associated complexity offarmland communities onorganic
farms inoldculture landscapemayrequireamoredetailed assessmentoffunctional group
assemblages inthe farm food web.
Theincreased food availability tobirds intheriverregionwas suggested bythetotal songbird
territory density: 10-12territories/10ha,whichwastwotosixtimesmorethanonten selected
Flevoland farms inthe 1997-1999observations.Inoneofbothriverregion farms, skylarks
had adensity of2.7territories/10ha,whichwashigherthanthehighest observed density (2.4
territories/10ha)inFlevoland. Infarm food webs inoldculture landscape comparedto
polders,resources suppliedbyweeds,bothdirectly (seeds) andindirectly (herbivores),might
haveparticularimportance.AlsocontributionsoftheE.I.tothe farm food webinoldculture
landscape,maynot onlyincludeorganisms from herbaceous vegetation but also from habitats
(e.g.woody,aquatic)thataremorecontrastingtofarmland communities.
Itcanbe arguedthat itwouldbemoredifficult toassess(i.e.isolate)the effects of farm
management (e.g.involving detritis input inthecroparea)inoldculture landscapethanin
polders.Morecomplex systemsmayinvolvemore extensive ecosystem services andnature
conservation contributions thatdonot (yet)occur insimpler agroecosystems (Brown, 1999a;
111
Altieri, 1994).Studies should,therefore, soonerorlater,also addressthemore complex
farmland communities inmorebiodiverse landscapes (Stobbelaar &VanMansvelt,2000;
Edwardsetal., 1999;Vandermeeretal.,1998).
1.4. Implications
1.4.1. Implicationsfor improvementofecosystemserviceandnatureconservation aims
Withregardtoimprovingtheutilisation ofecosystem services(Altieri, 1999),ourresults
implythatenhancing theprey availability for epigeicpredators,bysubsidising thedetrital
subweb,mightcontributetopestcontrolonorganic arable farms. Thismechanism may
alreadybeaninfluence onlongduration organic farms with extensive croprotation (including
aleypasture).However, further researchonthistopicisnecessary andpromising.
Increasingtheabundance ofvegetation dwelling (oligophagous) predators inthecropcanopy,
mightnotbeanappropriate aim,becausethegreat abundanceofcropherbivoreswouldbe
needed toincreasethesepredators.Thisisinagreementwithreportsonthelimited predation
capacityofoligophagouspredators (e.g. CoccinellidaeinHemptinne&Dixon, 1997).
Withreference tothenatureconservation goals,results suggestthatimprovement ofE.I.
enhancesthedensityofinsectivorousbirds,whicharethemainconservation-worthyspecies
onarable farms. Thecrop areasofintensiveorganicarablefarms supported relatively high
densitiesofinsectivorousbirds(when compared withrecently converted farms), possibly
related totheoccurrence ofr-herbivores.
However, ifthesesystemsweretobeoptimised, inaccordancewiththeprinciples outlined
above,theincreased employment ofepigeicbeneficials mightruncountertohighbird
densitiesi.e. natureconservation values.Anincreased efficacy ofweedcontrol inthe future,
might further diminishthefood resourcesinthecropareaavailable for thesebirds.Itmight
appearcuriousthatcurrent organic farming systemsinFlevoland withanintensivecropping
system (andparticularly whenthereisalsoanimproved E.I.)combinetogether,toa
reasonabledegree,both aimsofproviding ecosystem services andnatureconservation,but
that further improvement oforganic farming systemsmightreducethis integration.
1.4.2. Furtheragroecologicalimplications offood webmanagement
TheimportanceofK-herbivores aspreyfor insectivorousbirds aswell astheimportanceof
herbivorousvertebrates for toppredators suggeststherelevance, from anenergypointof
view,ofrelativelysmallfood chains('flows') inthefarm food web.Probablymost
consumptionbyherbivores iscarried outbysmallorganisms liker-herbivores (i.e.aphids)
(Smeding &DeSnoo,2001).Because90%ofenergyislost ineachtransfer inthe food chain
(Polis&Winemiller, 1996),food chainsthat start from smallprimary organisms, dissipate
moreenergy,before tissuesareassimilated intothelargerorganism-'meat';primary
consumptionby largeherbivores (e.g. leatherjackets,chafers, grasshoppers,sawfly larvae,
caterpillars,mice)mightbemoreeffective for thehighertrophic levelsofthefarm foodweb.
Inthedetrital food web asimilar arbitrary divisionbetweenthesmallprimary organism
chainsand largeprimaryorganism chainscouldbemade:micro-organism based chains(De
Ruiteretal.,1995)versussaprovorous arthropods (e.g. flies, large springtails) and
earthwormsbasedchains,which connect tovertebrates,for example, lapwingand
insectivorousmammals.
Foodwebmanagement,whichisaimedatnatureconservation goals,mayaddress,in
particular, thelargeorganismchains.Thiscouldbedonebyincreasingtheamount ofless
nutritive andmorecomplexplanttissues,aswellasthedetritusthat doesnot decompose
112
easily inboth thecrop areaandtheE.I.;theseresourcesrequiretheemployment ofthelarger
organismsmentioned above.Accordingly,Ryszkowski etal.(1993)found morelargespecies
inarablecrops inmosaic landscapes {i.e. including ahighamountof'E.I.')than inarable
cropsinuniform landscapes.
Cousins(1996),whowasasourceofinspiration for thechapter on food webstructure,
stressedtheimportanceofweighting thefood 'value'inafood web.Fromthisviewpoint, for
example seedsand flower products, althoughprincipally belongingtoprimary production,
maybeput onthe sametrophic level asaphids.Accordingly, detrituswith ahigher fibre
content,mayhaveahigher 'value'than easily decomposablematerial whichisimmediately
decomposedbythemicropredator system.However,theseprinciples shouldnotbeapplied
toorigorously; for example,Steffan-Dewenter &Tscharntke (1997)found morelargesized
catterpillars inpioneer successional fields than inlatesuccessional fields. Another aspectis
that largerorganisms often have longerlife cycles;therefore alsophysical disturbance and
shelterpossiblities,onbothfieldandfarm level,shouldbeconsidered {e.g. Ryszkowski etal.,
1993;Brown, 1999b).
Themanagement ofcomponentsthatarenotharvested (NHC)(Vandermeeretal, 1998),
included intheconcept ofmulti-species farms,providesaconceptualbasis for afood web
management that specifically addressesthe'largeprimaryorganism chains'.Centraltothe
management ofNHC istherecognition oftheimportance ofcropresidues,hay from thecanal
banks, andothernon-harvestedmaterials(includingthestandingcropofwildvegetationand
trees)for thefarming system and itsfood web.Primaryproduction capacity,whichdoesnot
feature intheeconomicreturnsofthe farm {e.g. greenmanure,E.I.vegetation) mightbeused
asalife support for thenon-pest herbivore subweb andsubsequently support the detritivore
subwebmacrofauna. Betterhabitatconditions fortheseherbivoresmaycompensatetosome
extent forthepredationpressurebyepigeicpredators,duetodetrital subsidy. Insuchan
extended food web structure, ecosystem services andnatureconservationmight againbe
integrated. However,thequestionwhethercomplex food websarebetter i.e. morestablethan
simplefoodwebsisaperennialtopic fordiscussion amongecologists (Polis&Winemiller,
1996),andmightbemoredifficult toapproachthanotherquestionsraisedbythisparagraph.
Swift &Anderson (1993)aswellasWardle(1999)arguedthatthedetrital subwebonarable
farms ismoredeveloped andlessdepletedthantheherbivore subweb.Ourstudies,however,
suggest,inreference totheabovegroundcommunity,thatthereisanequalsignificance for
boththeherbivore subwebandthedetrital subweb(Smeding &DeSnoo,2001):
agroecosystemsinwhich alltheNHC enterthedetritivorous food chainsmaynot support
highdensitiesofvertebrates.From afood webperspective itmight therefore be achallengeto
incorporate controlled herbivory inmulti-species farming systems(e.g.Theunissen, 1994,
1997;Andow, 1988;Altieri, 1994;Holland &Fahrig,2000).
2. Recommendations
2.1Improvementoftopologicalweb
Theassemblage offunctional groupsandtheidentification ofinteractionsbetweenthese
functional groups aretheempirical foundation offood web studies (Winemiller &Polis,
1996).Peculiarities of speciesmay,insomecases,determine food web structure.Therefore it
isimportant to elaborateonthis foundation byextracting information ondiet,habitat
preferences and life history shifts from thevast amountofavailable literature {e.g. Paoletti,
1999).This information iscurrentlybeingcollected inadatabaseAURYN (Booij,Lockand
113
Smeding,unpublished data),andwillbeused toupdatethetopological food webspresented
inthisthesis.
2.2. Linkingfood Miebs tofarm models
Thechangesoffarm food web structurerelated to farm andE.I.characteristics (Smeding&
DeSnoo,2001)couldbedescribed byamathematical model.Intheexploratoryphaseof food
webmanagement, simplemodelsmayhelptoexplorethehypotheses andtodetect theoretical
inconsistency.Apreliminarymodel isbeingdeveloped usingFuzzyCognitive Mapping
(Wolfert, inprep),which cancalculate,basedoncertain farm and E.I.traits,relative sizesof
thefunctional groupsinthefarm foodweb.
Foodweb analysismayinthefuture profit from extensive farm modelsthatcalculatethe
availabilityofresources fortheprimary functional groupsinthefarm food web(e.g. Oomen
&Habets, 1998;Wolfert, 1998;Wolfert etal.,1997).Thesemodelscould estimate,basedon
dataofthecroprotation andmanurestrategy,theamountsofvarioustypesofprimary
production andcropresidues (NHC)that areneeded tosupport theprimary consumption in
thefoodweb.Suchmodelscouldbeusedtodesignrealistic experimental and commercial
farms, withfor exampleoptimised detrital subsidy.
Thesubject ofthisthesiswasexplorative research describing arthropod andbird communities
that gaveanindication offood webstructure.However, inthefuture morequantitative data
setsandbetterunderstanding ofprocesses infarm food webs areexpected todeliver useful
simulationmodels.
2.3Spatialapproaches
Thespatialapproach(e.g. Opdam, 1986;Wratten&Thomas, 1990;DenBelderetal., in
prep.) andthefood web approach arebothuseful asaconceptual framework for
agroecological studiesatthecommunity level(VanWingerden &Booij, 1999).Authoritiesof
the food web approach (Polisetal, 1996;Winemiller&Polis, 1996)arguethatboth
approachesshouldbecombined,butalsonotethattheresultingcomplexitycouldbeaserious
constraint. Accordingly, connecting spatialmodelstoimportant functional groupsinthe food
webmodelwillposegreatproblems,bothintechnical andmethodological respect. However,
itmightbeachallenge forboth food web andspatialapproaches toexperiment withrather
simplecomprehensive models(e.g. Kreuss &Tscharntke, 1994).Theeffect onthe farm food
webstructureoftheE.I.arthropod community, and alsoofcropmosaics, exemplify spatial
heterogeneity. Accounting for themobilityof functional groups isnecessary for the
successful application of food web management.
Thespatial approach,based onthedispersal ofindividuals andpopulations (e.g. Topping,
1997)isessentially a'bottomup'approach. However, characteristics onahigher integration
levelshouldalsobeapproached withtheappropriatemethodsforthishigherlevel
(Almekinders etal., 1995;Cousins, 1996).Examples ofaspatial approach that addresses
higherintegration levelsareprovidedbytheworkofOldeman(1990),analysing spatial
patternsbasedonthedistinction of'eco-units'.
114
2.4.Fieldexperiments
Fieldresearch and experimentation arerequired toinvestigate thepreliminary conclusions
providedbythisthesis.Astudyareamight includebothcommercial farms aswellas
experimental farms. Theexperimental farms couldrepresent extremeregimesofmanagement
which arenotyet acceptable for farming practice.Careshouldbetakenwithexperimentsthat
involveplotswheretherearemany smallfields,whichmayrepresent amosaic from afarm
levelperspective.Thecontext and scaleofa(farming) systemmayinsomecasesbea
precondition fortheoccurrenceofparticulareffects (e.g. Pimm, 1991;Brown, 1999a).
Comprehensive field studieswith indiscriminate assessment ofmanytaxa, asdonebyPotts&
Vickerman(1974),maymodelfieldresearchthatcouldoptimally support food webstudies.
2.5.Practicalrecommendations
Procedures for farm-nature planswererecently elaboratedbyVanAlmenkerk &Van
Koesveld (1997),Visser (2000) andDaemen(2000).Protocols orprocedures for such
combined agricultural andecologicalplansmightbesupportedbyarestricted food web
assessmentbasedonsimpleassumptions.Forexample,asimplemodelthat appliesdatafrom
the farm map(areasofcropsandhabitats),coarsemanuring strategy, andE.I. management,
mayprovideestimatesofresource availability for several functional groupsonthe farm.
Theseoutcomesmayhelpthe farmer oradvisertosetpriorities,withregard tohabitatsor
speciesgroupsthat couldbe andaretobe enhanced.
115
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129
Summary
Species diversityofindigenousplantsandanimalsonfarmland isdeclining dramatically due
toagricultural intensification. Biodiversity lossinagriculture affects both economicand
natureconservation values.Oneimportant solution forthereversal ofbiodiversity lossinthe
agriculture ofindustrialised countriescouldbethedevelopment offarming systemsthatare
economicallybasedonutilisation ofbiodiversity andthat alsoharbourconservation worthy
species.This ideaiscompatiblewiththeconcept ofmulti-species agroecosystems.
Development oforganic farming systemsisapossible implementation ofthisconcept;crop
areasmanaged accordingtothisconceptmaybecomplementedby anadjacent ecological
infrastructure (E.I.)-Afood web approachisanappropriatemethod for investigations intothe
higher integration levelsofecosystems andmaytherefore contributetoresearch onmultispecies farming systems.Progressinscientific understanding of food webs iscurrently
expanding into agroecology.Afood web approach alsoprovides aframework for orderingthe
scattered information onfarmland speciesandhabitats.
Asimplified setofhypotheses withregardto food web structure onorganic farms servedas
thestartingpoint forthethesis:itwasexpectedthattheduration oforganic management,
extensive croprotation aswellasanimproved E.I.(i.e.enlarged areaand latemowed),would
relatepositivelytothe abundance ofarthropods inbothnon-pest herbivorous and
detritivorousprimary subsystems.Thevariedplanttissuesinimproved E.I.would particularly
boostthenon-pest herbivorous functional groups.Consequentlypredator andparasitoid
numbersonthe farm wouldbe supported. Anaccumulated highinvertebrate densityonthe
farm would support insectivorous vertebrates,particularly birds.Theobjectives ofthethesis
were:totake acomprehensive food web approachinrelationtothe farm andE.I.
management; tolinkcomponentknowledge onspecies and farm operationstofoodweb
theories;andtopoint outimplications formulti-species farm development. The studyarea
involved farms thatweremainly situatedintherelatively uniform landscape ofFlevoland.
Thispolderhas aconcentration oforganicarable farms, including farms with improved E.I.
Empirical investigationswereconcentrated onparticular sectionsofthefarmland community,
namelyground dwelling arthropods,vegetation dwelling arthropods and insectivorousbirds.
Functional group compositions (e.g. detritivores,herbivores andpredators)within these
sectionswere assessed.Field studies indicated that allthe factors included inthe above
hypothesis affected abundance and functional groupcomposition ofboth arthropods and
birds.However,theeffects differed from whatwas expected.
Inthecroparea(i.e.wheatcrops),K-herbivore abundancewasrelated tofarms thathadbeen
recently converted andr-herbivore abundancewasrelated to farms ofalonger duration with
anintensive croprotation.Boththeobserved herbivore increasesmightbe explainedbya
combination ofcrop susceptibility totheherbivore group,andlimitedpredation pressure
(Chapter2).Therewas,accordingtothehypothesis, someevidence for detritivoreincrease
related toextensive croprotation onlongduration farms and for detrital subweb-connected
predator increase inrelationtomore extensive farms (Chapters 2and 3).Predator abundance
inthecropcanopywasparticularly related tohighK-herbivore numbersonrecently
converted farms. Thehighest speciesdiversitywasfound onlongduration farms whichhad
anintensivecroprotation (Chapter 2).The farmswhichhad anextensive croprotation,
compared with theother farms, had alowpredatornumber inthecropcanopy,whereasthe
parasitoids had intermediatenumbers.Thedensity ofbirds' territories seemed tobeenhanced
bythecropareasofthoselong duration organic farms thathad anintensive croprotation,this
beingpossibly related toan increased herbivory (Chapter4).
131
Anincreased arthropod abundancewas found inthevegetation oftheimproved E.I.The
increased functional groupsincludedbothpredators anddetritivores (Chapter 2).However,
K-herbivore numbersdidnotincreaseintheimproved E.I.whentheywerecompared tothe
traditionallymanaged E.I.(Chapter 2and3);perhapsbecausetheprolonged vegetative
development offrequently mownvegetationmight extendtheavailability ofnutritive grass
tissue.Also,theabundance oftheepigeicpredators,inparticularofthe quantitatively
importantgroupofpredaciousbeetles,wasnotrelated toanimproved E.I.(Chapter3).
Observations suggested thattheirnumberswererelated tothecrop areaconditions.Open,
frequently mownE.I.vegetation enhanced themorespecific ground dwelling functional
groups,whencompared toimproved E.I.Theterritorial densityofinsectivorousbirdswas
showntobepositively relatedtothehigh arthropod abundance intheE.I.(Chapter4).
Field studiesprovided someevidencefor thedispersal offunctional groups,abundantinthe
E.I.intothecrop area.However,theeffects ofcropconditions onthearthropod abundancein
thecropareawereobserved tooffset theinfluence oftheE.I. for somegroups.Contraryto
expectations,observations suggested theoppositeeffects regarding flying arthropods,which
werepossiblytransported intotheE.I.,andepigeicpredaciousbeetles(Chapters 2and3).
Bird studies(Chapter4)revealedpositive correlationsbetweenbirdfunctional groupsanda
combination ofcrop areaandE.I.characteristics.Thismay suggestthatboththecropareaand
theE.I.habitatsareimportant tothesebirds.Thismay alsoholdtrue for birdsthattypically
liveintheE.I.,because acertainproportion oftheirpreycouldoriginate inthecroparea.
Inthediscussion sectionofeach empirical studyobservationswere linkedtotheoryin food
webliterature.Fieldobservationsprovided someindications for indirect effects ofsubsidised
detrital food chainsonherbivore abundance andconsequentlyonbird abundance,aswellas
possible effects ofintraguildpredation onarthropod functional groupcomposition. However
extrapolation oftheresultsobtained inFlevoland toothergeographical regionsmayrequirea
further examination offunctional group assemblages,andofprimaryresources relatedto
weedsortosemi-natural habitatsotherthanherbaceoushabitat (Chapters 5and8).
Aproposal for adescriptiveortopological farm food webisdrawn from field observations as
wellasfrom references inliterature (Chapter 6).Important themesinthe food webtheory
weretentatively applied tothispreliminary model inexplaining differences between localised
farm foodwebstructures andhowtheyarerelatedtothefarm and/orecological infrastructure
management. Predictions aremadefor four different farm food webstructuresthat express
four extremesoftwoenvironmental gradientswhichcorrespond tothelength oforganic
duration andtheamount/qualityoftheE.I.Empirical observations areusedtoillustratethe
different food web structures.However, further investigation isnecessary toconfirm the
hypothesesput forward.
Theimplications ofbothempirical aswell asconceptual studies arethattheorganic duration
andtheamount/qualityoftheecological infrastructure maybothpositivelycontributeto
improvingecosystem services andtoaimsbasedonnatureconservation.However,an
optimisation ofthefarm food webwithregardtoecosystem servicesmayrun counterto
natureconservationvalues,asinthecaseofenhanced epigeicpredators whichwoulddepress
herbivorous food items forbirds.Nevertheless anincreased understanding ofthefarm food
webanditsmanagement islikelytoshowmoreclearlythepossibilities for the development
ofmulti-species agroecosystemsthat integrate ecosystem services andnature conservation
goals.Theoutcome ofthiskind ofapplied ecological research islikely toimprovethebasisof
pragmatic protocols for farm-nature planning exemplified inChapter 7.
132
Samenvatting
Desoortsdiversiteit endeaantallenvanwildedieren enplanten inlandbouwgebieden gaan
achteruit tengevolgevanintensivering vandelandbouw. Ditverliesaanbiodiversiteit heeft
nadelen voorzoweleconomiealsnatuurbescherming. Aanwending vanecosystem servicesin
verbandmetbiodiversiteit, zoukunnenbijdragen aaneenverminderdeinzetvanbestrijdingsmiddelen,meststoffen enfossiele brandstoffen. Dezeecosystemservicesworden mogelijk
dooreenkleinegroepvanessentielesoortenverzorgd.Echtervanuithetoogpuntvannatuurbescherming isbrede stimuleringvanbiodiversiteit gewenstomdatlandbouw veelruimte
gebruikt enspecifieke leefgemeenschappen omvat.Eenmogelijke oplossingvoorhet
geschetsteprobleem ishet ontwikkelen vanlandbouwsystemen diebiodiversiteit benutten en
instandhouden enduslandbouw ennatuurbescherming ophetniveauvan een landbouwbedrijf verenigen.Verschillende agroecologen hebbenditthemauitgewerkt. De Amerikaanse
onderzoeker Vandermeer noemtdergelijke landbouwsystemen 'multi-speciesagroecosystems'
(Vandermeer etal., 1998);ditbegripvatdedoelstellingvandezethesissamen.
Onderzoekdienstigaanhetontwikkelenvanmulti-speciesagroecosystemsinde praktijk
verlangt eenspecifieke opzet.Watbetreft hetobject ishetbelangrijk dathet onderzochte
systeem degewenste specifieke complexiteitbezitomdatdegezochteprocessen mogelijk
alleen ineendergelijke context optreden.Vanuit dezeoverwegingisgekozenomop
biologische landbouwbedrijven onderzoek tedoenenmetnameopbiologischebedrijven met
randomdepercelen eenecologische infrastructuur (E.I.)dieverbeterd is,d.w.z.vergroot qua
oppervlak enecologischbeheerd. Watbetreft demethodeishetbelangrijk dathet onderzoek
kenmerkenmeetophetsysteemniveau.Vanuit dezeoverwegingisgekozenvooreen
voedselwebbenadering, overeenkomstigdeaanbevelingen van Gezondheidsraad (1997)met
hetoogopecosysteemanalyse.Uitgangspunten enuitwerkingenvandebenaderingzijn te
vindeninhet gezaghebbende werkvanPolis&Winemiller(1996).Inagroecosystemen (inde
gematigde streken)verkeert voedselwebonderzoek nogineenoverwegend exploratieve fase
metbijvoorbeeld fundamentele studies aanhetdetrituswebvanDeRuiter etal.(1993,1995)
enhypothese-ontwikkelende artikelenvanWiseetal.(1999),Brussaard (1998) enTscharntke
(1997).
Hetonderzoeksdoelvoorditproefschrift wasdrieledig:
-het opstellenvan eendescriptief ('topologisch')voedselweb voor eenbiologisch
akkerbouwbedrijf, datzowelhetonder-alsbovengrondse systeemomvatendatgeschiktis
voorhet leggenvanrelatiesmethandelingen vandeboer;
-het leggenvanverbanden tussen componentkennis (diersoorten, teeltmaatregelen en
biotoopbeheer), enecologische theorievanuitdevoedselwebbenadering, om zodoende
aanwijzingen tevindenvooreffecten opbedrijfsniveau van voedselwebinteracties;
-zoekrichtingen aangevenvoorhet ontwikkelen vanbedrijfssystemen diehetbenutten van
'ecosystem services'ennatuurbescherming combineren.
Dehypothese vanhetonderzoekbestaatuit eenserie,vanuit deliteratuur onderbouwde,deelhypothesentenaanzienvandevoedselwebstructuur.Dezehypothesewasdateroplang
(geleden)omgeschakeldebedrijven meteenverbeterde E.I.eenrelatief grotedichtheid isvan
mesofauna enmacrofauna vandeprimairefunctionele groepen. Dedetritivoren worden
bevorderd dooreenextensievevruchtwisseling metgranen enkunstweiden dieveel
organische stofachterlaten,enookdoororganische mest.Deherbivoren, enmetnamenietplaagsoorten, hebbenrelatiefhogedichtheden doordeaanwezigheid vanveelverschillende
gewassen enwat talrijkere onkruiden. DeE.I.bevordert vooral deaantallen herbivoren
vanwegehaargroterevariatieaanplantenweefsels, inclusiefbijvoorbeeld bloemen enzaden.
133
Bij detoenamevandeprimaire functionele groepen enhunvoedselbronnen spelen
cumulatieveeffecten overdejarenmee.Detoegenomen dichtheid vanbeideprimaire
subsystemendraagthethogeretrofische niveauvandeongewerveldepredatoren en
parasitoiden.Deverhoogde dichtheden vandezegroepenwerken deexponentiele toename
vanplaagherbivoren tegen.Vervolgens isdetotaledichtheid vanzoweldepredatoren alsde
primaire groepenvanbelang alsvoedsel voorinsectenetende vogelsophetbedrijf. De
dichtheid vanpredatoren,parasitoiden envogelswordtdusverondersteld toetenemenin
verband metomschakelingsduur enE.I.-kwaliteit.
Hetonderzoekbestond uitveldonderzoek enliteratuurstudie.Hetveldonderzoek was vrijwel
beperkt totFlevoland omdatlandbouwbedrijven daareenovereenkomstigetopografie en
historiehebben. Ookbevindt zichinFlevoland eenconcentratie vanongeveer 75biologische
akkerbouw- envollegrondsgroenteteeltbedrijven, waaronderbedrijven met een verbeterde
ecologische infrastructuur.
Inhetveldonderzoek werdenwaarnemingenverricht aanepigeische geleedpotigen door
middelvanvangbekers,vegetatiebewonende insecten doormiddelvan eenzuigapparaat,en
insectenetende vogelsdoormiddelvanterritoriumkarteringen.Ongewervelden werden
verzameld intarwevelden enindeernaast gelegen slootkanten.Vogels en
omgevingsvariabelenwerdengemetenop bedrijfsniveau.
Deresultaten vandeveldonderzoeken lieten,overeenkomstigdehypothese,effecten zienop
dehoeveelheden van functionele groepen,vandeduurvandebiologische bedrijfsvoering,
intensiteitvandevruchtwisseling endeomvangenhetmaaibeheer vandeE.I.
Indegewassenblekenherbivoren echterhettalrijkst tezijn oppasomgeschakelde bedrijven
meteenweelderiggewas;typischeplaagherbivoren (bladluizen) hadden dehoogste
dichtheden oplangomgeschakelde bedrijven meteenintensievevruchtwisseling (Hoofdstuk
2).Waarnemingen aandetritivoren wezenwelmeerinderichtingvandehypothese.
Detritivoren (vliegjes enmugjes)warenoplangomgeschakeldebedrijven meteenextensieve
vruchtwisseling relatieftalrijk (Hoofdstuk 2). Ookepigeischepredatoren (o.a.loopkeversen
spinnen),diewaarschijnlijk vooral verbonden zijn metdetritivoreketens,lekentalrijker te
zijn insystemenmeteenextensievere teeltwijze (Hoofdstuk 3).Predatoren inhet bladerdek
vanhetgewasblekengeassocieerd tezijnmetherbivoren; dezewarentalrijk inweelderige
gewassenvanpasomgeschakeldebedrijven enwarendiversqua soortenoplang
omgeschakeldebedrijven meteenintensievevruchtwisseling (Hoofdstuk 2).
HetverbeterdebeheerindeE.I.had,overeenkomstig dehypothese eensterkpositiefeffect op
dedichtheid vanarthropoden enmetnamepredatoren indevegetatie(Hoofdstuk 2).
Detritivoren waren echterdetalrijkste primairegroep;herbivorenwarenweliswaar talrijk
maarhadden eenovereenkomstige dichtheid inE.I.methettraditioneleklepelbeheer. De
talrijkste epigeischegroepenvanpredatorekeversenbaldakijnspinnen vertoonden eengewasaffiniteit (Hoofdstuk 3).Andere,mindertalrijke groepen,zoalswolfspinnen warenmeer
geassocieerd metklepelbeheer danmethetverbeterdebeheer.Verbeterde E.I.haddus(inde
zomer)voorepigeische soortenweinigbetekenis.Waarnemingen indegewas-E.I.gradient,
lietenziendathogedichtheden indeE.I.kunnenuitstralen inderichtingvanhetgewas.De
omstandighedeninhet gewaswaren echteroverheersend enkondenzulkeeffecten tenietdoen
ofaanhetzichtonttrekken,bijvoorbeeld ingevalvandetoenamevanherbivoren en
predatoren ineenweelderiggewas.
Dedichtheid vaninsectivorebroedvogelsbleekgeassocieerd tezijn metzowel
bedrijfs/gewaskenmerken, alsmetE.I.kenmerken (Hoofdstuk 4).Watbetreft het bedrijf,
134
suggereren deresultaten dat langomgeschakelde biologischebedrijven met eenintensieve
vruchtwisseling,dehoogstevogeldichtheid hadden.Mogelijkbevordert deperiodieke
toenamevanplaagherbivoren devoedselbeschikbaarheid. Watbetreft deE.I.werden
duidelijke verbanden gevonden tussenvogeldichtheid enverhoogdedichtheid van
arthropodengroepen indevegetatievandeE.I.
Indediscussiesvaniederempirischonderzoek (hoofdstukken 2,3en4)zijn deresultatenin
verband gebrachtmetvoedselwebtheorieen. Develdwaarnemingen gaven indicaties voorhet
optredenvaneenindirectnegatief effect vantoegenomen detritivorevoedselketens,via
bevordering vanpolyphagepredatoren, opdedichtheid vanherbivoren. Enook indicaties
voormogelijke interacties tussenpredatorengroepen.Verderonderzoek isechter
noodzakelijk.
Inhoofdstuk 6isopbasisvanliteratuur enveldonderzoek eentopologisch voedselweb
opgesteld.Devariatieindestructuurvanditvoedselweb isvoorspeld aandehandvanvier
extremebedrijfstypen dietweegradientenrepresenteren watbetreft deduurvanbiologische
bedrijfsvoering enE.I.kwaliteit. Aanvullend isnogonderscheid gemaakt tussen lang
omgeschakeldebedrijven metverbeterdeE.I.,watbetreft dematevanherbivorie inhun
gewassen. Thema'sdienaarvorenkwamenindediscussiesvandeempirischeonderzoeken
(hoofdstukken 2,3en4)werdenondergebracht inhetgrotereverband vanhetvoedselweb op
bedrijfsniveau. Overeenkomstigdeoorspronkelijke hypothese,isdeaanvoervan
voedselbronnen vanonderafinhetvoedselweb alsbepalend aangewezen ('bottomup'
processen).Mogelijk zijn echterookterugkoppelingen vanbovennaarbeneden inhet
voedselwebbelangrijk ('top down'effecten). Zulkeeffecten tredenopalsepigei'sche
predatoren,bevorderd doordetritivoreprooien,herbivoreprooisoorten onderdrukken. Een
complete onderdrukking vanplagen enookvanandereherbivoren kanechter ongunstig zijn
voordichtheden vaninsectenetende vogelsomdatdezegroep inbelangrijke mategevoed
wordtviaherbivorevoedselketens ophetlandbouwbedrijf. Ecosystemservicesen
natuurbelang zijn dan tegenstrijdig.
Destudie laatziendat eenvoedselwebbenadering veelbelovend is;hiermeeisonderzoek
mogelijk aandeeffecten vaninteracties inhet voedselweb,inclusief gevolgen voor landbouw
ennatuurdoelen. Eventuele tegenstrijdigheid kandeaanleiding zijn tezoekennaar
alternatieventeroptimalisatievanbeidedoelen.Verderonderzoek isechter zeer
noodzakelijk.
Naastdedriehoofdstukken overveldonderzoek inFlevoland enhethoofdstuk methet
conceptuelemodel,isereenempirischhoofdstuk 5dat eenstudietoontvandiergroepenop
tweebiologischebedrijven inFlevoland entweeinhetrivierengebied. Inbeide landschappen
waseenbedrijf met veeleneenbedrijf metweinig E.I.Dezewaarnemingen tonen echter
vooral het contrast tussendelandschappen. Extrapolatie vandeFlevolandse gegevensnaar
andere landschappen ismogelijk maarverlangt mogelijk uitbreiding vande functionele
groepen eneenbeter zicht opdebijdragen aandeze functionele groepen (inclusiefprooienen
predatoren) vanbijvoorbeeld houtigebiotopen enonkruiden.
Hoofdstuk 7beschrijft eenprocedure voorhetopstellenvanbedrijfsnatuurplannen. Dit
instrument ispragmatisch enstreeft naarzogoedmogelijke ontwerpen opbasisvan
ecologischekennis,veldbiologie enpraktischemogelijkheden. Doorhet expliciet makenvan
doelen encriteriaisgetracht omdestappenvanwaarneming,viawaardering naar beslissing
teverhelderen enookteversnellen. Devraaginhoeverre eenbedrijfsnatuurplan effectief is
voorhetbevorderen vanpredatoren ofbijzondere dieren,waseenaanleiding totde
voedselwebstudies. Verderonderzoek opbasisvanditproefschrift kanindetoekomst
bijdragen aanadviesinstrumenten tenbehoevevanmultispeciesfarming systems.
135
Curriculum Vitae
FransWouter Smeding wasborn onthe4thSeptember 1962inMeppel,TheNetherlands.He
graduated from theAthenaeum oftheStedelijk Lyceum inZutphen, in 1981,and
subsequently studiedBiology attheWageningen Agricultural University.Hespecialisedin
vegetation science,plant ecology andweed scienceaswell asalternative methodsin
agriculture andhorticulture.Heachieved hisMScinMarch 1989,including a qualification
forfirstdegree education. In 1989-1990hecontributed tothesettingupofunsprayedfield
marginresearch atthedepartment ofVegetation science,Plant ecologyand Weed science.In
November 1990hestartedtowork atthedepartment ofEcological Agriculturewherehe
participated inongoingresearch andinternational educationprograms withreference to
holisticapproaches.Hehasspecialised there,since 1992,ontheintegration ofagriculture and
nature.Incollaboration withtheDutch agricultural extension service,hedeveloped in
1994-1995aprotocol for farm-nature plans.Thisworkwas followed byexplorative research
on farm food webs inrelationtothemanagement ofcropandfieldmargins (1996-2001).He
iscurrently employed aslecturerbytheWageningenUniversity andResearch Centre,atthe
BiologicalFarming Systemsgroup,DepartmentofPlant Sciences.
137

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