GeneralEcology(BIO160)
Worksheet#8
Dept.ofBiologicalSciences
SacramentoStateUniversity
Worksheet8:Theecologicalniche
1. Whatisthedefinitionofahabitat?Anyplacewhereanorganismlivesthatmeetstherequirements
foritssurvivalandreproduction.
2. Whatisthedifferencebetweenanenvironmentalfactorandaresource?Anenvironmentalfactor
influencestheabilityoforganismstosurvive,growandreproducebutisnotactuallyusedbythe
organism.Acrosstherangeofconditionsthatanyspeciesexperiences,therewillbeanoptimal
rangeofconditions(i.e.,factors)overwhichitcanthrive(i.e.,achieveadequategrowthand
reproduction).Bycontrast,aresourceisacomponentoftheenvironmentthatanorganismuses
andthatisnecessaryforitssurvival,growthand/orreproduction.Forexample,plantstakeup
nitrogeninthesoilandcarnivoresconsumetheirprey.Therefore,bothnitrogenandpreyare
consideredresourcesbecausetheorganismuseseach.However,soilpHinthecaseofplantsand
temperatureforcarnivoreswouldbeenvironmentalfactorsbecausetheyinfluencethesurvival,
growth,and/orreproductionbutarenotusedbytheorganism.
3. Abioticfactorsintheenvironmentcontinuallychangefromonelocationtoanother.Weseethis
everyplacewelook.Forinstance,meanannualtemperaturedecreaseswithincreasingaltitude;the
intensityofphotosyntheticradiationdeclineswithincreasingwaterdepth;soilmoisturecontent
tendstodiminishwithincreasingdistancefromawaterbody;andsoon.Ifyouweretomeasure
theperformanceofaspeciesacrosstherangeofvariationinanyoftheseconditionsyouwouldtend
toobserveacharacteristicunimodalresponsecurveofthatspeciestothatcondition.Thisiscalled
theecologicalresponsecurve.
a. Usinganabioticfactor/conditionofyourchoice,drawtheecologicalresponsecurveyoumight
expectforaspeciesacrosstherangeofthatcondition.This
exampleplotselevationvs.performanceforaplantspecies.It ce
n
a
assumesthatperformancewilldropoffrapidlyatthehighest
m
r
Reprod.
elevations.Reproductionwouldlikelyoccuratthenarrowest
fo
re
P
Growth
andmostoptimalrangethangrowthandsurvival.
Survival
Treenestingheight
Elevation
b. Indicateonyourresponsecurvetherangeofthatconditionoverwhich
youmightexpectthehighestperformancetooccurintermsofsurvival,growth,and
reproduction.Whichoftheserequiresthemostoptimalconditions?Seeabove.
4. Thenicheconceptisacentralconceptinecology.Answerthefollowingquestionsregardingthe
ecologicalniche.
a. Howdoestheconceptofthenichedifferfromthatofahabitat?Whereasahabitatisaphysical
placewhereaspecieslives,thenicheisanabstract“space”(oftendepictedgraphically)thatis
definedbytheconditionsitrequiresandtheresourcesituses.
b. Namesomecharacteristicsofaspeciesthatcanbeusedtodefineitsecologicalniche.Foraging
location,foodsize,nestinglocation,seasonality,vegetationtype,etc.
GeneralEcology(BIO160)
Worksheet#8
Dept.ofBiologicalSciences
SacramentoStateUniversity
c. Therealizednicheofaspeciescandiffersubstantiallyfromthatofitsfundamentalniche.What
isthedifferencebetweenthesenichespacesandhowiseachdetermined?Thefundamental
nicheofanorganismisdefinedbythefullrangeofresourcesitcanusetosurviveandreproduce
withoutinterferencefromotherspecies.Therealizednicheistheactualobservednichea
speciesoccupiesinthefaceofinteractionswithotherspeciesthatlimititsuseofresourcesit
mightotherwisebeabletouse.Thefundamentalnichecanonlybemeasuredbyremoving
otherspeciesthatarepresumedtointerferewiththefocalspecies’useofresourcesandthen
quantifytherangesofresourcesituseswithoutthoseinteractions.Therealizednichecanbe
measuredbyquantifyingtherangesofresourcesthespeciesusesinthepresenceof
interactionswithotherspecies.
d. Drawadiagramillustratingthefollowingterms:nicheoverlap,nichebreadth,andniche
separation.SeeFigure11.10inyourtextforagoodillustration.
e. Whatistheconsequenceofhighnicheoverlapfortwospeciesusingasingleresource?What
effectcanhighnicheoverlaphaveontheevolutionoftraitsintwosuchspecies?Highniche
overlapresultsinahighintensityofcompetitionbetweenthespeciesforthoselimiting
nutrientswherethenichesofthespeciesoverlap.Inevolutionaryterms,whenintense
competitionoccursbetweentwospecieswheretheirnichesoverlapitcancreatestrong
directionalselectionthatreducesnicheoverlapandthereforecompetitionbetweenthespecies.
5. ThreespeciesofAnolislizardsperchandfeedintreesofaforest.
Eachspeciesdiffersinitsperchpreferences,foodsource,and
aggressivebehaviors.Thearrows(A-E)inthediagramatright
illustratefivepossiblehabitatniches(eitherfundamentalor
realized)oftheselizardspeciesinthetreesinwhichtheylive.The
behavioraltraitsofeachlizardspeciesareprovidedbelow.
Anolisopalinus:canperchandfeedinthelowertwothirdsofthetreebutisrestrictedtothevery
bottomofthetreebyaggressivebehaviorofAnolisgrahamifromabove.
Anolisvalencienni:canperchandfeedintheentiretophalfofthetreebutisrestrictedtothevery
upperbranchesbyaggressivebehaviorofA.grahamibelow.
Anolisgrahami:canperchandfeedacrosstheentireheightofthetreebutisrestrictedtothemiddle
branchesbyaggressivebehavioroftheothertwoAnolisspeciesaboveandbelow.
a. Whicharrow(A-E)abovebestrepresentstherealizednicheofA.grahami?A
b. Whicharrow(A-E)abovebestrepresentsthefundamentalnicheofA.opalinus?E
c. Whicharrow(A-E)abovebestrepresentstherealizednicheofA.valencienni?D