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2、亚马逊雨林的消亡之路研究人员揭示了不同规模的生态系统消失的速度，一旦达到临界点，它们就会崩溃，然后变成另外一个生态系统。即便是庞大到像亚马逊雨林这样的超级生态系统，也难以摆脱逐渐消失的命运。面对这样的巨变，我们该何去何从呢？阅读短文并回答问题Largeecosystems（生态系统）,suchastheAmazonrainforest,willcollapseanddisappearalarminglyquickly,onceacrucialtippingpointisreached,accordingtocalculationsbasedonreal-world
3、data.Writingin NatureCommunications,researchersfromBangorUniversity,SouthamptonUniversityandtheUniversityofLondon,revealthespeedatwhichecosystemsofdifferentsizeswilldisappear,oncetheyhavereachedapointbeyondwhichtheycollapse—transformingintoanalternativeecosystem.Forexample,oncethe“pointofn
4、oreturn”isreached,theAmazonrainforestcouldshifttoasavannah-typeecosystemwithamixoftreesandgrasswithin50years,accordingtotheresearch.Somescientistsarguethatmanyecosystemsarecurrentlyteetering（摇晃）ontheedgeofacliff,withthefiresanddestructionofboththeAmazonandAustralianrainforests.“Unfortunate
5、ly,whatourpaperrevealsisthathumanityneedstoprepareforchangesfarsoonerthanexpected,”saysjointleadauthorDrSimonWillcockofBangorUniversity.“Theserapidchangestotheworld’slargestandmosttypicalecosystemswouldimpactthebenefitswhichtheyprovideuswith,includingeverythingfromfoodandmaterials,totheoxy
6、genandwaterweneedforlife.”Ecosystemsmadeupofanumberofinteractingspecies,ratherthanthosedominatedbyonesinglespecies,maybemorestableandtakelongertoshifttoalternativeecosystemstates.“Theseecosystemsprovideopportunitiestomitigateormanagetheworsteffects”,saytheauthors.Forexample,elephantsareter
7、meda“keystone”speciesastheyhaveadisproportionately（不成比例地）largeimpactonthelandscape—pushingovertrees,butalsodispersingseedsoverlargedistances.Theauthorsstatethatthelossofkeystonespecies,suchasthis,wouldleadtoarapidanddramaticchangeinthelandscapewithinourlifetime.“Thisisyetanotherstrongargum
8、enttoavoiddegradingourplanet’secosystems;weneedtodomoretoconservebiodiversity,”saysDrGregoryCooper,UniversityofLondon.1.Whatisthephenomenondescribedinparagraph2?A.Manyecosystemsareindangercurrently.B.Largeecosystemshavereachedatippingpoint.C.Anewecosystemwilla
