Chapter 05 INTRASPECIFIC COMPETITION.docx
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Chapter 05 INTRASPECIFIC COMPETITION.docx
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Chapter05INTRASPECIFICCOMPETITION
Chapter05INTRASPECIFICCOMPETITION:
POPULATIONREGULATION(种内竞争:
种群调控)
Densitydependenteffectsinfluenceapopulationinproportiontoissize.
∙Atlowdensity,nointeractionoccurs;asthepopulationgrowsbeyondcertainpoint,thegreaterthenumberofindividualsaffected.
Density-dependentmechanismsactlargelythroughshortagesandcompetitionforresources.
INTRASPECIFICCOMPETITION
Competitionisthesimultaneousdemandbytwospeciesortwoindividualsforanessentialcommonresourcethatisactuallyorpotentiallyinlimitedsupply.
Aresourceisacomponentoftheenvironmentthatcanbeutilizedbytheorganismforhelporsupport.
Iftheresourceisenoughsupplythereisnocompetition.
Theformofcompetitioninwhichthecompetingindividualsdonotinteractwitheachotherwhenexploitingtheresourceiscalledexploitativecompetition.Theindividualsdonotreacttoeachotherbuttothelevelofresource.
Wheneachindividualcompetingfortheresourceobtainssuchasmallsupplyoftheresourcethatnonecansurvive,itcalledacompetitionscramble.
Contestcompetitionistheformofintraspecificcompetitioninwhichmortalitycompensatesexactlyforincreasesindensity,sothatthereisaconstant(orapproximatelyconstant)numberofsurvivorsirrespectiveofinitialdensity.
∙Contestcompetitioncanbecalledinterferencecompetition.
∙Ifthememberofthepopulationinteractdirectlyseekingaresourcethatisnotlimiting,e.g.fight,theinteractioniscalledcontestorinterferencecompetition.
∙Someindividualsgetalltheresourcesandtheothersdonotreproduce,migrateordie.
EFFECTSONGROWTHANDFECUNDITY
Populationscharacterizedbyscrambleorexploitativecompetition,individualsrespondtoloweredleveloffoodbyreducinggrowth.Theanimalsdonotgrowlargesothebiomassremainsthesame,e.g.manysmallindividuals=fewerlargeindividuals.
Densityalsoaffectsfecundity.
Insomepopulations,competitioncausestheanimalstogrowataslowerpaceandreachmaturityatalatertime.
Insomelargemammalpopulations,competitiondoesnotaffectthefecundityofthepopulationuntilthepopulationdensityreachesanumberclosetoK,thecarryingcapacity,andthenfecundityisreducedandthebirthratedeclineswithincreasingdensity.
Inotherlargemammalpopulation,thebirthdeclineislinearwithpopulationgrowthandincreasedensity.
EFFECTSONPLANTBIOMASS
Inplants,ahighdensityofseedlingsinanareawillnothaveaninitialeffectontheindividuals.Eventually,however,competitionforcanopyspace,rootspace,nutrients,water,andlightintensifies.
Asindividualsinacompetingpopulationofeven-agedplantsgrow,theirmeanbiomassalsoincreasesandtheirnumberdecreases.
Afewindividualsout-competetheothersandgrowfaster.Otherslacktheabilitytocompeteanddie.
Theresultisathinningofthestandandadevelopinghierarchyofsizewithafewlargeandmanysmallindividuals.Thisiscalledself-thinning.
Howsoonthepopulationwillfeeltheeffectsontheincreasingweightandsizeoftheplantsdependsontheinitialdensity.Iftheinitialdensityishigh,theeffectslikemortalityandreducedgrowthwillbefeltsooner.
Regardlessoftheinitialdensity,populationseventuallyconvergeonacommondensitythatwilldecreasethroughtime.
∙Thefinalresultisthesameregardlessofthenumberofindividualsintheoriginalpopulation.
Theaverageplantvolumeorweightincreasesabout1.5unitsforeachunitdecreaseindensity.
o-3/2powerlawofselfthinning.
oThelogarithmmeanweightorvolumeplottedagainstthelogarithmofplantdensity,theslopeofthelineaveragesaround-3/2or-1.5.
oAllpopulationseventuallyreachthesamepointwherepopulationdeclinesasplantvolumeincreases.
Anotherwayofsayingtheself-thinninglaw:
oincrowdedpurestands,themeanplantbiomassshouldbeproportionaltoa-3/2poweroftheirdensities
Thethinninglawappliestoeven-aged,single-speciesstands.
oTheplantsareofsimilarshaperegardlessofsize.
oThecanopyis100%closed.
Inmixedstandsofmanyspecies,thelawseemstoapplyinabroadsense.
DENSITYANDSTRESS
Stresscausesphysiologicalchangesinvertebratesinvolvingtheendocrinesystem.
Thepituitaryandadrenalglandsareaffectedbystress.
Stressfulenvironmentalstimulus
↓
Hypothalamusreleasescorticotrophinreleasingfactor(CRF)
↓
Anteriorpituitaryreleasesadrenocoticotropichormone(ACTH)
↓
Adrenalglandsreleasecortisol
↓
Cortisolcausesareactioninthebody,e.g.increaseinbloodsugar
Stresstriggershyperactivationofthehypothalamus-pituitary-adrenocorticularsystem,whichinturnaltersthesecretionofgrowthandsexhormones.
Thehyperactivationoftheendocrinesystemsuppressesgrowth,slowsdownreproductivefunction,anddelayssexualactivity.
Hormonalchangesmaycausethebreakdownofinwhitebloodcellsincreasingthevulnerabilitytodiseases.
Socialstressinpregnantfemalesmaycausespontaneousabortionandinadequatelactationthatwillproducestuntednurslings.
Stresscanresultindecreasedbirths,andincreasedmortality.
∙Stressreactionvarieswiththeindividual.
∙Itprobablyhasageneticcomponent.
∙Prolongedexposuretoastressfulstimulusaffectsthereaction.
∙Knowledgeandearlierexperiencesinfluencethereactionsysteminhumansandanimals.
Pheromonesarechemicalsreleasedbyanimalsthatserveascommunicationbetweenindividualsofthesamespecies.
Pheromonesintheurinemaydelaypubertyofyoungfemalesinhighdensitypopulations.
Therearedifferentkindsofpheromonesthatproducedifferenteffectsonothermembersofthepopulation,e.g.aggregation,attack,flight,changesindevelopment,territoriality,etc.
Plantsrespondtohighdensityinavarietyofways:
reducingthenumberofnodes,thelengthoftheinternodes,numberofflowersandseeds,leavesperstem,andbranches.
Genetsmayproducefewerrametsincrowdedconditions.
Someruderalplantsreducetheirvegetativepartsincrowdedconditionsbutproducealargenumberofseedsthatwillstaydormantuntildisturbanceexposestheseedstolightandfluctuatingdailytemperatures.
Somebiennialsundercompetitivestressdelayreproductionforthreetofiveyears.
Ingeneral,lowerproportionofplantssurvivestomaturityundercrowdedconditions.
MECHANISMSOFPOPULATIONREGULATION
Dispersal
Severalhypotheseshavebeenproposedtoexplaindispersalasawayofcontrollingpopulationdensity.
Thereisevidencethatdispersaloccursbeforethepopulationreachesitspeakandbecomesovercrowded,andalso,thereisevidencethatdispersaloccurswhenthepopulationreachesitssaturationpoint.
Presaturationdispersal:
∙Thepopulationisincreasing.
∙Beforereachingthecarryingcapacityandresourcesaredepleted.
∙Dispersersareingoodphysicalcondition.
∙Dispersersareofanyageandsexgroup.
∙Haveachanceofsurvival.
∙Haveahighprobabilityofsettlinginanewarea.
Saturationdispersal:
∙Itoccurswhencarryingcapacityhasbeenexceeded.
∙Dispersersaremostlyjuvenilesandsubdominants
∙Havetwooptionstostayandeitherperishornotbreed,ortoleavethearea.
Dispersalrequiresanunfilledhabitat,suitableornot,wherethedispersercansurviveforatime.
Somehypotheses:
∙Aggressivenessofdominantadultscausesdispersal.
∙Somegenotypesaremorepronetodispersethanothersandwilldisperseregardlessofdensityconditions.
∙Asocialindividuals,eitherdominantorsubdominant,failtodevelopsocialtiesandaremorelikelytodisperse.
Therecostsandbenefitsrelatedtodispersalorwithstayingathome.
Doesdispersalregulatepopulations?
Dispersalmayfunctioninpopulationregulationbyencouragingmostlysubadultsandpossiblysomesubdominantindividualstoleavetheirnatalareaandoccupyvacanthabitats.
Successfullydispersingindividualsimprovetheirfitnessbydoingso.
SOCIALINTERACTIONS
Socialbehaviorappearstobeamechanismthatlimitsthenumberofanimalsthatcanliveinaparticularhabitat,haveaccesstofoodsupply,andengageinreproductiveactivities.
Socialbehaviorinvolvesaggressiveandsubmissivebehaviorexpressedassocialdominanceandterritoriality.
SOCIALDOMINANCE
Socialdominanceisbasedonintraspecificaggressivenessandintoleranceandonthedominanceofoneindividualoveranother.
Eachindividualoccupiesappositioninthegrouporlocalpopulationbasedondominanceandsubmissiveness.
Thepositioninthesocialhierarchymaydependonanumberoffactors:
levelofhormones,size,maturity,injury,fatigue,experienceinfighting,etc.
Peckingordermaytakeseveralforms:
∙Linearinwhichthedominantindividualpecksonanotheroflowerrank;thelastinthepeckingsequenceissubservienttoallothermembersofthegroup.
∙Triangular:
onepecksonnumbertwo,whointurnspeckofnumberthree;andnumberthreepecksonnumberone.
∙Complexpeckingoccurwhenindividualspeckoneachother,andthedominantpecksthemosttimes.
Malesandfemalesmayhaveseparatehierarchyinmixedgroupswithmalesdominantoverfemales;orfemalesequaltomales;ormalessubservienttofemales.
Strangercomingintoagroupareeitherrejectedorarerelegatedtothebottomofthesocialorder.
Often,malesandfemalesthatcomeintobreedingearlyriseinthesocialorderdueincreaseaggressiveness.
Dominantindividualshavethefirstchoiceoffood,shelterandspace,andsecuremostmates.Subdominantindividualsoftenhavetowaittoeat.
TERRITORIALITY
Thesocialorganizationinvolvingthedivisionandexclusiveoccu
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