托福阅读题及答案
<p>托福阅读真题：</p><p><span word="The">The</span> <span word="Long">Long</span>-<span word="Term">Term</span> <span word="Stability">Stability</span> <span word="of">of</span> <span word="Ecosystems">Ecosystems</span></p><p><span word="Plant">Plant</span> <span word="communities">communities</span> <span word="assemble">assemble</span> <span word="themselves">themselves</span> <span word="flexibly">flexibly</span>, <span word="and">and</span> <span word="their">their</span> <span word="particular">particular</span> <span word="structure">structure</span> <span word="depends">depends</span> <span word="on">on</span> <span word="the">the</span> <span word="specific">specific</span> <span word="history">history</span> <span word="of">of</span> <span word="the">the</span> <span word="area">area</span>. <span word="Ecologists">Ecologists</span> <span word="use">use</span> <span word="the">the</span> <span word="term">term</span> “<span word="succession">succession</span>” <span word="to">to</span> <span word="refer">refer</span> <span word="to">to</span> <span word="the">the</span> <span word="changes">changes</span> <span word="that">that</span> <span word="happen">happen</span> <span word="in">in</span> <span word="plant">plant</span> <span word="communities">communities</span> <span word="and">and</span> <span word="ecosystems">ecosystems</span> <span word="over">over</span> <span word="time">time</span>. <span word="The">The</span> <span word="first">first</span> <span word="community">community</span> <span word="in">in</span> <span word="a">a</span> <span word="succession">succession</span> <span word="is">is</span> <span word="called">called</span> <span word="a">a</span> <span word="pioneer">pioneer</span> <span word="community">community</span>, <span word="while">while</span> <span word="the">the</span> <span word="long">long</span>-<span word="lived">lived</span> <span word="community">community</span> <span word="at">at</span> <span word="the">the</span> <span word="end">end</span> <span word="of">of</span> <span word="succession">succession</span> <span word="is">is</span> <span word="called">called</span> <span word="a">a</span> <span word="climax">climax</span> <span word="community">community</span>. <span word="Pioneer">Pioneer</span> <span word="and">and</span> <span word="successional">successional</span> <span word="plant">plant</span> <span word="communities">communities</span> <span word="are">are</span> <span word="said">said</span> <span word="to">to</span> <span word="change">change</span> <span word="over">over</span> <span word="periods">periods</span> <span word="from">from</span> 1 <span word="to">to</span> 500 <span word="years">years</span>. <span word="These">These</span> <span word="changes">changes</span>—<span word="in">in</span> <span word="plant">plant</span> <span word="numbers">numbers</span> <span word="and">and</span> <span word="the">the</span> <span word="mix">mix</span> <span word="of">of</span> <span word="species">species</span>—<span word="are">are</span> <span word="cumulative">cumulative</span>. <span word="Climax">Climax</span> <span word="communities">communities</span> <span word="themselves">themselves</span> <span word="change">change</span> <span word="but">but</span> <span word="over">over</span> <span word="periods">periods</span> <span word="of">of</span> <span word="time">time</span> <span word="greater">greater</span> <span word="than">than</span> <span word="about">about</span> 500 <span word="years">years</span>.</p><p><span word="An">An</span> <span word="ecologist">ecologist</span> <span word="who">who</span> <span word="studies">studies</span> <span word="a">a</span> <span word="pond">pond</span> <span word="today">today</span> <span word="may">may</span> <span word="well">well</span> <span word="find">find</span> <span word="it">it</span> <span word="relatively">relatively</span> <span word="unchanged">unchanged</span> <span word="in">in</span> <span word="a">a</span> <span word="year">year</span>’<span word="s">s</span> <span word="time">time</span>. <span word="Individual">Individual</span> <span word="fish">fish</span> <span word="may">may</span> <span word="be">be</span> <span word="replaced">replaced</span>, <span word="but">but</span> <span word="the">the</span> <span word="number">number</span> <span word="of">of</span> <span word="fish">fish</span> <span word="will">will</span> <span word="tend">tend</span> <span word="to">to</span> <span word="be">be</span> <span word="the">the</span> <span word="same">same</span> <span word="from">from</span> <span word="one">one</span> <span word="year">year</span> <span word="to">to</span> <span word="the">the</span> <span word="next">next</span>. <span word="We">We</span> <span word="can">can</span> <span word="say">say</span> <span word="that">that</span> <span word="the">the</span> <span word="properties">properties</span> <span word="of">of</span> <span word="an">an</span> <span word="ecosystem">ecosystem</span> <span word="are">are</span> <span word="more">more</span> <span word="stable">stable</span> <span word="than">than</span> <span word="the">the</span> <span word="individual">individual</span> <span word="organisms">organisms</span> <span word="that">that</span> <span word="compose">compose</span> <span word="the">the</span> <span word="ecosystem">ecosystem</span>.</p><p><span word="At">At</span> <span word="one">one</span> <span word="time">time</span>, <span word="ecologists">ecologists</span> <span word="believed">believed</span> <span word="that">that</span> <span word="species">species</span> <span word="diversity">diversity</span> <span word="made">made</span> <span word="ecosystems">ecosystems</span> <span word="stable">stable</span>. <span word="They">They</span> <span word="believed">believed</span> <span word="that">that</span> <span word="the">the</span> <span word="greater">greater</span> <span word="the">the</span> <span word="diversity">diversity</span> <span word="the">the</span> <span word="more">more</span> <span word="stable">stable</span> <span word="the">the</span> <span word="ecosystem">ecosystem</span>. <span word="Support">Support</span> <span word="for">for</span> <span word="this">this</span> <span word="idea">idea</span> <span word="came">came</span> <span word="from">from</span> <span word="the">the</span> <span word="observation">observation</span> <span word="that">that</span> <span word="long">long</span>-<span word="lasting">lasting</span> <span word="climax">climax</span> <span word="communities">communities</span> <span word="usually">usually</span> <span word="have">have</span> <span word="more">more</span> <span word="complex">complex</span> <span word="food">food</span> <span word="webs">webs</span> <span word="and">and</span> <span word="more">more</span> <span word="species">species</span> <span word="diversity">diversity</span> <span word="than">than</span> <span word="pioneer">pioneer</span> <span word="communities">communities</span>. <span word="Ecologists">Ecologists</span> <span word="concluded">concluded</span> <span word="that">that</span> <span word="the">the</span> <span word="apparent">apparent</span> <span word="stability">stability</span> <span word="of">of</span> <span word="climax">climax</span> <span word="ecosystems">ecosystems</span> <span word="depended">depended</span> <span word="on">on</span> <span word="their">their</span> <span word="complexity">complexity</span>. <span word="To">To</span> <span word="take">take</span> <span word="an">an</span> <span word="extreme">extreme</span> <span word="example">example</span>, <span word="farmlands">farmlands</span> <span word="dominated">dominated</span> <span word="by">by</span> <span word="a">a</span> <span word="single">single</span> <span word="crop">crop</span> <span word="are">are</span> <span word="so">so</span> <span word="unstable">unstable</span> <span word="that">that</span> <span word="one">one</span> <span word="year">year</span> <span word="of">of</span> <span word="bad">bad</span> <span word="weather">weather</span> <span word="or">or</span> <span word="the">the</span> <span word="invasion">invasion</span> <span word="of">of</span> <span word="a">a</span> <span word="single">single</span> <span word="pest">pest</span> <span word="can">can</span> <span word="destroy">destroy</span> <span word="the">the</span> <span word="entire">entire</span> <span word="crop">crop</span>. <span word="In">In</span> <span word="contrast">contrast</span>, <span word="a">a</span> <span word="complex">complex</span> <span word="climax">climax</span> <span word="community">community</span>, <span word="such">such</span> <span word="as">as</span> <span word="a">a</span> <span word="temperate">temperate</span> <span word="forest">forest</span>, <span word="will">will</span> <span word="tolerate">tolerate</span> <span word="considerable">considerable</span> <span word="damage">damage</span> <span word="from">from</span> <span word="weather">weather</span> <span word="to">to</span> <span word="pests">pests</span>.</p>
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