Chapter 06 INTERSPECIFIC COMPETITION.docx

Chapter 06 INTERSPECIFIC COMPETITION.docx

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Chapter06INTERSPECIFICCOMPETITION

Chapter06INTERSPECIFICCOMPETITION（种间竞争）

Individualsofonespeciesinteractwithindividualsofanotherspecies.

Theeffectsofthoseinteractionsonpopulationgrowthcanbeneutral,positiveornegative.

1.Neutralinteractionshavenoeffectonthegrowthofthepopulation.Thisiscalledneutralism.

2.Positiveinteractionsbenefitbothorganisms.Theyarecalledmutualism.

3.Commensalismoccurswhenonspeciesbenefitsandtheotherisnotaffectedinanyway.

4.Amensalismisthecoactioninwhichonespeciesisadverselyaffectedbyotherspecies,whichremainsunaffected.

5.Predationisthekillingandconsumptionofaprey.

6.Parasitismisinaninteractioninwhichoneorganism,usuallysmall,livesinoronanotherfromwhichitobtainsfood.

Thereisadverseeffectonthetwospeciesorindividualsthatcompeteforaresourcethatisinlimitedsupply.Thisinteractionbetweenspeciesisinterspecificcompetition.

Interspecificcompetitionmaybeexploitativeorinterference.

Exploitationmeansthattheindividualtakesasmuchoftheresourceasitcanbutdoesnotinteractwithothermembersofthepopulation,e.g.eachpigatatroughhasaplaceandeatsasmuchasitcould.

∙Thefocusofcompetitionisthefood.

Interferenceisthetypeofintraspecificcompetitionthatinvolvesinteractionbetweenindividuals,e.g.lionseatingazebrainwhichthenon-dominantlionscannotgetaplacetofeedandhavetowaituntilthemoredominantanimalshavefinished.

Placebecomesthefocusofcompetitionratherthanthefood.

CLASSICCOMPETITIONTHEORY

THELOTKA-VOLTERRAMODEL.

TheLotka-Volterrapredatorymodelassumesthatthenumberofpredatorsdependonthepreypopulation.

LotkaandVolterraarrivedindependentlytomathematicalexpressionsthatdescribetheinteractionbetweentwospeciesusingthesameresource.

Bothbeganwiththelogisticequationforpopulationgrowth:

∙forspecies1andspecies2

dN1=r1N1（K1–N1）

dtK1

dN=instantaneousrateofchange

dt

N=numberofindividuals;

r=bioticpotential

t=time

K=carryingcapacity

（K-N）itisameasureoftheenvironmentalresistanceortheeffectof

Kcrowding.Thisrepresentstheopportunityforfurtherpopulation

growth.

dN2=r2N2（K2–N2）

dtK2

theythenaddedtothelogisticequationforeachspeciesacoefficienttoaccountforthecompetitiveeffectofonespeciesonthepopulationgrowthofanother.

Forspecies1,αN2isthecoefficientthatgivesthecompetitiveeffectofspecies2.N2isthenumberofspecies2individualsandαisthecompetitiveimpactperindividualofspecies2onspecies1.

Thisconstantconvertsthenumberofmembersofonespeciespopulation,2,intoanequivalentnumberofmembersoftheother,1.

Forspecies2,thecoefficientisβN1.

Thepairedequations,whichnowconsiderbothintraspecificandinterspecificcompetitionare…

dN1=r1N1（K1–N1–αN2）

dtK1

dN2=r2N2（K2–N2–βN1）

dtK2

Inthelogisticequation,asthenumberofindividualsineachpopulation（N）increasestowarditscarryingcapacity（K）,thegrowthofthepopulation（dN/dt）approacheszero.

Theadditionofeachnewindividualhasaninhibitoryeffectonitsfurtherpopulationgrowth:

intraspecificcompetition.Thisinhibitoryeffectofspecies1onitselfis1/K1,anofspecie2onitselfis1/K2.

Theinhibitoryofeffectofeachnewindividualofspecies2onspecies1isα/K1,andeachnewindividualofspecies1onspecies2isβ/K2.

Anyonespecieswillstopgrowingwhenitscarryingcapacityhasbeenreachedbythecombinationofitsownnumbersplustheindividualsoftheotherspeciesmultipliedbytheappropriatecompetitioncoefficient

Species1willstopgrowingwhenN1+αN2=K1

Species2willstopgrowingwhenN2+βN1=K2

WhenN2is0,thenN1=K1;whenN1is0,thenN2=K1/α.

WhenN1is0,thenN2=K2;whenN2is0,thenN1=K2/β

Thepresenceofspecies1decreasesthecarryingcapacityofspecies2,andviceversa.

ThetwospecieswillreachequilibriumwhendN1=dN2=0

dtdt

SEEGRAPHSONPAGE245.MAKESUREYOUUNDERSTANDTHESEGRAPHSANDCANINTERPRETTHEM.

TheLotka-Volterramodelproducesacyclicpopulationcurveshowingthepopulationfluctuationofpreyandpredator.

Itistoosimpletofitanyrealinteractingpopulationsofpreyandpredator.

COMPETITIVEEXCLUSION

Gause'sruleorthecompetitiveexclusionprinciple

Twospecieswithidenticalecologicalrequirementscannotoccupythesameenvironment.

∙Twospeciescannotoccupythesameecologicalniche.

∙Completecompetitorscannotcoexist.

Conditionsfornecessaryforcompetitiveexclusiontotakeplace:

1.Resourcesareshortsupplyforcompetitiontotakeplace.

2.Competitorsmustremaingeneticallyunchangedforasufficientlylongperiodtotimeforonespeciest