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1、www.ylongedu.com新托福TPO19阅读原文(二)：Succession,Climax,andEcosystemsTPO19-2：Succession,Climax,andEcosystems Inthelatenineteenthcentury,ecologybegantogrowintoanindependentsciencefromitsrootsinnaturalhistoryandplantgeography.Theemphasisofthisnew"communityecology"wasonthecompositionandstructureofcom
2、munitiesconsistingofdifferentspecies.Intheearlytwentiethcentury,theAmericanecologistFredericClementspointedoutthatasuccessionofplantcommunitieswoulddevelopafteradisturbancesuchasavolcaniceruption,heavyflood,orforestfire.Anabandonedfield,forinstance,willbeinvadedsuccessivelybyherbaceousplants(
3、plantswithlittleornowoodytissue),shrubs,andtrees,eventuallybecomingaforest.Light-lovingspeciesarealwaysamongthefirstinvaders,whileshade-tolerantspeciesappearlaterinthesuccession. Clementsandotherearlyecologistssawalmostlawlikeregularityintheorderofsuccession,butthathasnotbeensubstantiated.Ag
4、eneraltrendcanberecognized,butthedetailsareusuallyunpredictable.Successionisinfluencedbymanyfactors:thenatureofthesoil,exposuretosunandwind,regularityofprecipitation,chancecolonizations,andmanyotherrandomprocesses. Thefinalstageofasuccession,calledtheclimaxbyClementsandearlyecologists,islike
5、wisenotpredictableorofuniformcomposition.Thereisusuallyagooddealofturnoverinspeciescomposition,eveninamaturecommunity.Thenatureoftheclimaxisinfluencedbythesamefactorsthatinfluencedsuccession.Nevertheless,maturenaturalenvironmentsareusuallyinequilibrium.Theychangerelativelylittlethroughtimeunl
6、esstheenvironmentitselfchanges. ForClements,theclimaxwasa"superorganism,"anorganicentity.EvensomeauthorswhoacceptedtheclimaxconceptrejectedClements'characterizationofitasasuperorganism,anditisindeedamisleadingmetaphor.Anantcolonymaybelegitimatelycalledasuperorganismbecauseitscommunicationsys
7、temissohighlyorganizedthatthecolonyalwaysworksasawholeandappropriatelyaccordingtothecircumstances.Butthereisnoevidenceforsuchaninteractingcommunicativewww.ylongedu.comnetworkinaclimaxplantformation.Manyauthorsprefertheterm"association"tothete
