阅读理解

AclassicseriesofexperimentstodeterminetheeffectsofoverpopulationoncommunitiesofratswasconductedbyapsychologistJohnCalhoun．Ineachexperimentanequalnumberofmaleandfemaleadultratswereplacedinanenclosure(场地)．Theratpopulationswereallowedtoincrease．Calhounknewfromexperienceapproximatelyhowmanyratscouldliveintheenclosureswithoutexperiencingstressduetoovercrowding．Heallowedthepopulationtoincreasetoapproximatelytwicethisnumber．Thenhefixedthepopulationbyremovingthechildrenthatwerenotdependentontheirmothers．AttheendoftheexperimentsCalhounwasabletoconcludethatovercrowdingcauseabreakdowninthenormalsocialrelationshipsamongratsakindofsocialdisease．Theratsintheexperimentsdidnotfollowthesamepatternsofbehaviorasratswouldinacommunitywithoutovercrowding．

Thefemalesintheratpopulationwerethemostseriouslyaffectedbythehighpopulationdensity(密度)．Forexamplemotherssometimesdesertedtheirchildrenandwithouttheirmothers'carethechildrendied．Theexperimentsshowedthatinoverpopulatedcommunitiesmotherratsdonotbehavenormally．Theirbehaviormaybeconsidereddiseasedadpathological(病理学的)．

Theleadingmalesintheratpopulationweretheleastaffectedbyoverpopulation．Eachofthesestrongmalesclaimedanareaoftheenclosureashisown．Thereforetheseindividualsdidnotexperiencetheovercrowdinginthesamewayastheotherratsdid．Howeverleadingmalesdidbehavepathologicallyattimes．Theirantisocial(反社会)behaviorconsistedofattacksonweakermalefemaleandimmaturerats．Thisunusualbehaviorshowedthateventhoughtheleadingmaleshadenoughlivingspacetheytoowereaffectedbythegeneralovercrowding．

Non-leadingmalesintheexperimentalratcommunitiesalsoexhibitedunusualsocialbehavior．Somewithdrewcompletelyavoidingcontactwithotherrats．Othernon-leadingmalesweretooactivechasingotherratsandfightingeachother．

Thebehavioroftheratpopulationhass