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Competition

Whenseveralindividualsofthesamespeciesorofseveraldifferentspecies
dependonthesamelimitedresource,asituationmayarisethatisreferredtoas
competition.Theexistenceofcompetitionhasbeenlongknowntonaturalists;its
effectsweredescribedbyDarwininconsiderabledetail.Competitionamong
individualsofthesamespecies(intraspeciescompetition),oneofthemajor
mechanismsofnaturalselection,istheconcernofevolutionarybiology.Competition
amongtheindividualsofdifferentspecies(interspeciescompetition)isamajor
concernofecology.Itisoneofthefactorscontrollingthesizeofcompeting
populations,andextremecasesitmayleadtotheextinctionofoneofthecompeting
species.ThiswasdescribedbyDarwinforindigenousNewZealandspeciesofanimals
andplants,whichdiedoutwhencompetingspeciesfromEuropewereintroduced.

当同一物种的不同个体或不同的物种都依靠同一有限资源时，这种情况往往会引发成所
谓的竞争。竞争的存在已为生物学家们所熟知，其结果也已被达尔文详尽叙述过。同一物种
不同个体之间的竞争(种内竞争)，作为自然选择的一个主要原理，现在属于进化生物学。不
同物种个体之间的竞争(种间竞争)是生态学的主要部分。它是控制有竞争关系的种群数量的
一个因素，而其极端情况可能导致竞争的一方灭绝。达尔文在描述新西兰本土动植物物种在
与引进的欧洲物种的竞争中灭绝时讲到该情况。

Noseriouscompetitionexistswhenthemajorneededresourceisinsuperabundant
supply,asinmostcasesofthecoexistenceofherbivores(plant
eaters).Furthermore,mostspeciesdonotdependentirelyonasingleresource,ifthe
majorresourceforaspeciesbecomesscarce,thespeciescanusuallyshiftto
alternativeresources.Ifmorethanonespeciesiscompetingforascarceresource,the
competingspeciesusuallyswitchtodifferentalternativeresources.Competitionis
usuallymostsevereamongcloserelativeswithsimilardemandsontheenvironment.But
itmayalsooccuramongtotallyunrelatedformsthatcompeteforthesame
resource,suchasseed-eatingrodentsandants.Theeffectsofsuchcompetitionare
graphicallydemonstratedwhenalltheanimalsoralltheplantsinanecosystemcome
intocompetition,ashappened2millionyearsagoattheendofPliocene,whenNorth
andSouthAmericabecamejoinedbytheIsthmusofPanama.NorthandSouthAmerican
speciesmigratingacrosstheIsthmusnowcameintocompetitionwitheachother.The
resultwastheextermination