Chapter18Community
Dynamics
BY470/570
CommunityStructureChangesthroughTime
Succession
•  Temporalchangeincommunitystructureata
givenloca@on
•  Whatchangestakeplaceinacommunityasit
changesthrough@me?
•  Whatdowecallthisprocessoftemporal
change?
CommunityStructureChangesthroughTime
CommunityStructureChangesthroughTime
Marine/Aqua@csuccession
CommunityStructureChangesthroughTime
Successionover@me
•  Asereisthesequenceofcommuni@esseenin
succession,fromgrasstoshrubtoforest
•  Eachofthechangesisaseralstage,apointon
thecon@nuumofvegeta@onthrough@me
CommunityStructureChangesthroughTime
Twomajortypesofsuccession
1)  Primary/earlySuccession—nopreviouscommunity
•  norealorganicmaQeratstart;slow
2)  Secondary/lateSuccession—previouscommunitythere
andremovedordisturbed
•  organicmaQer;fast
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PrimarySuccessionOccursonNewlyExposedSubstrates
PrimarySuccession
•  Asandduneisaninhospitablesitethatcan
undergoprimarysuccession
•  Plantcoverstabilizesthedunes
PrimarySuccessionOccursonNewlyExposedSubstrates
PrimarySuccessionOccursonNewlyExposedSubstrates
PrimarySuccessionOccursonNewlyExposedSubstrates
PrimarySuccessionOccursonNewlyExposedSubstrates
polartrec.com
SecondarySuccessionOccursaaerDisturbances
Secondarysuccession
•  Takesplaceatasitethatwaspreviously
occupiedbyacommunity
•  Physical&biologicaldisturbances:
e.g.agriculture,waves,preda@on,compe@@on,
etc
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SecondarySuccessionOccursaaerDisturbances
SecondarySuccessionOccursaaerDisturbances
SecondarySuccessionOccursaaerDisturbances
TheStudyofSuccessionHasaRichHistory
HistoryofSuccession
•  Ecologistshavebeenstudyingsuccessionfor
morethanacentury
•  Clements(1916,1936)-Monoclimax
hypothesisviewsthecommunityasahighly
integratedsuperorganism
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TheStudyofSuccessionHasaRichHistory
Ini@alfloris@ccomposi@on
•  Egler(1954)hypothesisproposedthatthe
processofsuccessionatanysitedependson
whichspeciesarrivefirst
•  Successionnotorderly,somefacilita@on&
someinhibi@on-individualis@c
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TheStudyofSuccessionHasaRichHistory
Connell&Slatyer(1977)–3models
–  Facilita3onmodel–earlysuccessionalspecieschange
theenvironment,makingitmoresuitableforlater
successionalspeciestoinvadeandgrow
–  Inhibi3onmodel–involvesstrongcompe@@ve
interac@ons
–  Tolerancemodel–speciesinearliersuccessional
stagesneitheraidnorinhibitlatersuccessional
species
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TheStudyofSuccessionHasaRichHistory
Grimestriangle(UAST)
•  R(ruderal)–speciesthatcanrapidlycolonize
disturbedsites
•  C(compe@@ve)–speciesthatlivein
predictablehabitatswithabundantresources
•  S(stress)–speciesthatarestress-tolerant
TheStudyofSuccessionHasaRichHistory
TheStudyofSuccessionHasaRichHistory
TheStudyofSuccessionHasaRichHistory
Successiondominance
•  PaQernofdominanceshiasduringsuccession
– early–fast-growing,shade-intolerantspecies
– later–slower-growing,shade-tolerantspecies
•  Resourcera@ohypothesis–successionisbased
onatrade-offincharacteris@csthatenable
plantstocompleteforlightandnitrogen
(essen@alresources)
SuccessionIsAssociatedwithAutogenicChangesinEnvironmentalCondi@ons
Autogenicvs.Allogenicchanges
•  Autogenicenvironmentalchangeistheresult
ofthepresenceandac@vi@esoforganisms
withinthecommunity
•  Allogenicenvironmentalchangeisaresultof
afeatureofthephysicalenvironment,sois
governedbyphysicalratherthanbiological
processes
PrimarySuccessionOccursonNewlyExposedSubstrates
SuccessionIsAssociatedwithAutogenicChangesinEnvironmentalCondi@ons
SuccessionIsAssociatedwithAutogenicChangesinEnvironmentalCondi@ons
Japaneseknotweed
•  Herbaceous,perennialplantna@vetoEastAsia,
Japan,China,&Korea
•  Lookslikebamboo
•  Stemsmaxheight3-4m(~10-13a)
•  Canbefoundintemperateriparianecosystems,
roadsides,dumps
•  Invasivespecies
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SuccessionIsAssociatedwithAutogenicChangesinEnvironmentalCondi@ons
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=0&p=0
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SpeciesDiversityChangesduringSuccession
Speciesdiversitychanges
SpeciesDiversityChangesduringSuccession
Intermediatedisturbancehypothesis
SuccessionInvolvesHeterotrophicSpecies
Heterotrophicspeciessuccession
•  Differentspeciesareseeninearlystagesof
successionthaninthelaterstages
–  Grasslandspeciesdisappear
–  Shrublandspeciescolonize
–  Eventuallytheshrublandspeciesdisappearand
arereplacedbyforestanimals
SuccessionInvolvesHeterotrophicSpecies
SuccessionInvolvesHeterotrophicSpecies
Systema@cChangesinCommunityStructureAreaResultofAllogenicEnvironmentalChangeataVarietyofTimescales
Allogenicenvironmentalchanges
•  Strictlyabio@cenvironmentalchangescanaffect
successionover@mescalesrangingfromdaysto
thousandsofyears,orlonger
•  Environmentalfluctua@onsthatoccurmany@mes
duringanorganism’slifespanareunlikelytoinfluence
successionalpaQernsamongspecieswithasimilarlife
span
•  Thesefluctua@onsareunlikelytoinfluencepaQernsof
secondarysuccessioninthosecommuni@es
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Systema@cChangesinCommunityStructureAreaResultofAllogenicEnvironmentalChangeataVarietyofTimescales
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CommunityStructureChangesthroughTime
Succession
•  Temporalchangeincommunitystructureata
givenloca@on
–  Facilita@on,inhibi@on,tolerance
–  RCSspecies
–  Autogenic&allogenic
–  Disturbancefrequency
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