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时间:2018-12-09
《焦点教育出品——托福阅读考题答案及解析:生态系统长期稳定_1》由会员上传分享,免费在线阅读,更多相关内容在教育资源-天天文库。
1、焦点教育出品——托福阅读考题答案及解析:生态系统长期稳定TPO托福阅读真题答案及解析:托福阅读文段的结构和出题点都有一定的规律,比如说托福阅读文段一般是总分总的格式,考生重点关注首段,尾段,转折句,开头句,基本上就能找到主题句,从这个方面来说,练习托福阅读真题,从中总结托福阅读考试经验是十分必要的,下面时代焦点教育为大家整理一份“TPO托福阅读真题答案及解析”,希望对大家有所帮助。托福阅读真题:TheLong-TermStabilityofEcosystemsPlantcommunitiesassemblethemselvesflexibly,andtheirparticularst
2、ructuredependsonthespecifichistoryofthearea.Ecologistsusetheterm“succession”torefertothechangesthathappeninplantcommunitiesandecosystemsovertime.Thefirstcommunityinasuccessioniscalledapioneercommunity,whilethelong-livedcommunityattheendofsuccessioniscalledaclimaxcommunity.Pioneerandsuccessional
3、plantcommunitiesaresaidtochangeoverperiodsfrom1to500years.Thesechanges—inplantnumbersandthemixofspecies—arecumulative.Climaxcommunitiesthemselveschangebutoverperiodsoftimegreaterthanabout500years.Anecologistwhostudiesapondtodaymaywellfinditrelativelyunchangedinayear’stime.Individualfishmayberep
4、laced,butthenumberoffishwilltendtobethesamefromoneyeartothenext.Wecansaythatthepropertiesofanecosystemaremorestablethantheindividualorganismsthatcomposetheecosystem.Atonetime,ecologistsbelievedthatspeciesdiversitymadeecosystemsstable.Theybelievedthatthegreaterthediversitythemorestabletheecosyst
5、em.Supportforthisideacamefromtheobservationthatlong-lastingclimaxcommunitiesusuallyhavemorecomplexfoodwebsandmorespeciesdiversitythanpioneercommunities.Ecologistsconcludedthattheapparentstabilityofclimaxecosystemsdependedontheircomplexity.Totakeanextremeexample,farmlandsdominatedbyasinglecropar
6、esounstablethatoneyearofbadweatherortheinvasionofasinglepestcandestroytheentirecrop.Incontrast,acomplexclimaxcommunity,suchasatemperateforest,willtolerateconsiderabledamagefromweathertopests.Thequestionofecosystemstabilityiscomplicated,however.Thefirstproblemisthatecologistsdonotallagreewhat“st
7、ability”means.Stabilitycanbedefinedassimplylackofchange.Inthatcase,theclimaxcommunitywouldbeconsideredthemoststable,since,bydefinition,itchangestheleastovertime.Alternatively,stabilitycanbedefinedasthespeedwithwhichanecosystemretu
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