关于海豹的生态学论文讲解

LoadingPopulationGrowthofAntarcticFurSeals:LimitationbyaTopPredator,theLeopardSeal?Ecology,79(8),1998,pp.2863–28771998bytheEcologicalSocietyofAmericaByRONGHuaAntarcticfursealsfeedsmainlyonkrillandvariousfishspeciesandispreyeduponbyotherspeciesofseals,killerwhales,orsharks.Thus,despitetheusualfocusonbottom-upforcescon-trollingsealsandseabirds,thereisconsiderablescopefortop-downforcestoplayimportantroles.InthispaperweexamineevidenceforcontrolofanAntarcticfursealpopulationbyleopardseals.TheAntarcticfursealpopulationintheSouthShetlandIslandsispresentlyrecoveringfromearly19th-centurycommercialexploitationandnearextinction.Thisrecoveryprovidesanopportunitytoinvestigatetheforcesresponsibleforchangesinvitalrates(reproduction,mortality,immigration,andemigration)thatultimatelydeterminetherelativesuccessofbreedingcoloniesandthefursealpopulationasawhole.MODELASSUMPTIONS:(1)theproportionofthepupcohortborneachdayisequaltothecorrespondingprobabilityfromanormaldistributionofbirthdates;(2)therewasnoleopardsealpredationatNA;(3)aconstantfractionofthelivepupsdieseachdayfromcausesotherthanleopardsealpredation(e.g.,starvation,storms,orcrushingbyadultmales).Conceptualmodelsofthepredator–preyrelationshipbetweenleopardsealsandAntarcticfurseals.Stronglydensity-dependentpredationmortalitywouldbecapableofmaintainingthefursealpopulationina‘‘predatorpit’’atlowdensities.Leopardsealshavemanyalternativestofursealsasprey,includingothersealspecies,seabirds,fish,andkrillTherefore,therateofpredationonfursealsbyleopardsealsmaybelessstronglydependentonpreydensitythantherateofpredationonmoosebywolves.Long-term,steadygrowthrulesoutcertainconceptualmodelsforthepredator–preyrelationshipbetweenleopardsealsandfurseals.Thepredationratemayevenbeinverselydependentondensity;thepercapitarateofpredationmaydeclinewithincreasingfursealdensity(Fig.5b).leopardsealpredatorsconsumeasubstantialfractionofthenetproduction,allowingfursealstoslowlyincreasetoalevelatwhichtheyareessentiallylimitedbysomeresourcesuchasfoodorspace(equilibriumdensityEF).AnexampleofasimplemodelwithunstabledynamicsatlowfursealdensityisshowninFig.5c.IfthefursealpopulationwasperturbedtoadensitybelowtheunstableequilibriumU,orifpredationmortalityincreasedsothatUbecamegreaterthanthefursealdensity,anacceleratingdeclinetoextinctionwouldensue.LeopardsealabundanceatseveralAntarcticislandsvariesdramaticallyfromyeartoyear,possiblyeveninacyclicfashion.ThisvariationalonecouldcauseshiftsinthepredationcurvesothatsomeyearsreflecttheconditionsofFig.5c,whileinotheryearspredationislower(asinFig.5b)orevenabsent.THANKSFORYOURATANTION