英语雅思优秀阅读英语雅思优秀阅读Whenwasthelasttimeyousawafrog?Chancesare,ifyouliveinacity,youhavenotseenoneforsometime.Eveninwetareasonceteemingwithfrogsandtoads,itisbecominglessandlesseasytofindthoseslimy,hoppingandsometimespoisonousmembersoftheanimalkingdom.Allovertheworld,andeveninremotepartsofAustralia,frogsarelosingtheecologicalbattleforsurvival,andbiologistsareatalosstoexplaintheirdemise.Areamphibianssimplyoversensitivetochangesintheecosystem?Coulditbethattheirrapiddeclineinnumbersissignalingsomecomingenvironmentaldisasterforusall?Thisfrighteningscenarioisinparttheconsequenceofadramaticincreaseoverthelastquartercenturyinthedevelopmentofoncenaturalareasofwetmarshland;homenotonlytofrogsbuttoallmannerofwildlife.However,asyet,therearenoobviousreasonswhycertainfrogspeciesaredisappearingfromrainforestsinAustraliathathavebarelybeentouchedbyhumanhand.Themysteryisunsettlingtosaytheleast,foritisknownthatamphibianspeciesareextremelysensitivetoenvironmentalvariationsintemperatureandmoisturelevels.ThedangeristhatplanetEarthmightnotonlyloseavitallinkintheecologicalfoodchain,butwemightbeincreasingouroutputofairpollutantstolevelsthatmayhavealreadybecomeirreversible.Frogscouldbeinadvertentlywarningusofacatastrophe.Anexampleofaspeciesoffrogthat,atfarasisknown,hasbecomeextinct,istheplatypusfrog.Likethewell-knownAustralianmammalitwasnamedafter,itexhibitedsomeverystrangebehaviour;insteadofgivingbirthtotadpolesinthewater,itraiseditsyoungwithinitsstomach.Thebabyfrogswereactuallybornfromoutoftheirmothersmouth.Discoveredin1981,lessthantenyearslaterthefroghadcompletelyvanishedfromthecrystalclearwatersofBooloumbaCreeknearQueenslandsSunshineCoast.Unfortunately,thisfreakofnatureisnottheonlyfrogspeciestohavebeenlostinAustralia.Sincethe1970s,nolessthaneightothershavesufferedthesamefate.