托福听力TPO16原文Lecture3
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托福听力TPO16原文Lecture3
下面就让小编来为大家介绍一下托福听力TPO16原文中Lecture3的文本内容吧,大家要好好
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TPO16ScriptLecture3
Professor:OK.Let’scontinueourdiscussionaboutanimalbehaviorbytalkingaboutdecisionsthat
animalsface,complexones.Animals,eveninsects,carryoutwhatlooklikeverycomplexdecisionmaking
processes.Thequestionishow.Imeannoonereallythinksthat,sayabeegoesthroughweighingthepros
andconsofpollinatingthisflowerorthatflower.Butthenhowdoanimalssolvecomplexquestions,questionsthatseemtorequiredecisionmaking.Theanswerwe’llproposeofcourseisthattheirbehavioris
largelyamatterofnaturalselection.Asanexample,let’slookatforagingbehavioramongbeavers.Beavers
eatplants,mostlytrees.Andtheyalsousetreesandtreebranchestoconstructtheirhomesinstreamsand
lakes.Sowhentheydoforageforfoodandforsheltermaterials,theyhavetoleavetheirhomesandgoup
onlandwheretheirmainpredatorsare.Sothereareanumberofchoicesthathavetobemadeabout
foraging.Soforexample,um...theyneedtodecidewhatkindoftreetheyshouldcutdown.Sometrees
havehighernutritionalvaluethanothers,andsomearebetterforbuildingmaterial,andsomearegoodfor
both...um...aspentrees.Beaverspeeloffthebarktoeatandtheyalsousethebranchesforbuildingtheir
shelters.Soaspensdodoubleduty.Butashtrees,beaversuseashtreesonlyforconstruction.Another
decisioniswhentoforageforfood.Shouldtheygooutduringthedaytimewhenit’shotteroutsideand
theyhavetoexpendmoreenergy,oratnightwhentheweatheriscoolerbutpredatorsaremoreactive?
Ok,buttherearetwomoreimportantissues,reallythemostcentral,themostimportant,OK?First,
let’ssayabeavercouldgetthesameamountofwoodfromasinglelargetreewhenithaslotsofbranches
asitcouldgetfromthreesmalltrees.Whichshoulditchoose?Ifitchoosesonelargetree,it’havetocarry
thatlargepieceofwoodbackhome,andluggingabigpieceofwood40or50yardsishardwork,takesa
lotofenergy.Ofcourseit’llhavetomakeonlyonetriptogetthewoodbacktothewaterOntheotherhand,
ifitgoesforthreesmalltreesinstead,itwilltakelessenergypertreetogetthewoodbackhomebutit’ll
havetomakethreetripsbackandforthforthethreetrees.Andpresumably,themoreoftenitwandersfrom
home,themoreit’slikelytobeexposedtopredators.Sowhichisbetter,asinglelargetreeorthreesmallhttp://bailiedu.com
trees?Anothercriticalissueandit’srelatedtothefirst,tothesizeissue,ishowfarfromthewatershouldit
gotogettrees.Shoulditbewillingtotravelagreaterdistanceforalargetree,sinceit’llgetsomuchwood
fromit?Beaverscertainlygofartherfromthewatertogetanaspentreethanforanashtree.Thatreflects
theirrelativevalues.Butwhataboutsize?Willittravelfarther
ForalargertreethanItwillforasmallertree?NowIwouldhavethoughtthebiggerthetree,the
fartherthebeaverwouldbewillingtotravelforit.Thatwouldmakesense,right?Ifyou’regoingtotravel
far,makethetripworthitbuybringingbackmostwoodpossible.Butactually,theoppositeistrue.Beavers
willcutdownonlylargetreesthatareclosetothewater.Theywilltravelfaronlytocutdowncertainsmall
treesthattheycancutdownquicklyanddragbackhomequickly.Generally,thefarthertheygofromthe
water,thesmallerthetreetheywillcutdown.They’rewillingtomakemoretripstohaulbacklesswood,
whichcarriesagreaterriskofbeingexposedtopredators.Soitlooksasthoughbeaversarelessinterestedinminimizingtheirexposuretopredatorsandmoreinterestedinsavingenergywhenforagingforwood,
whichmayalsoexplainwhybeaversforageprimarilyduringtheevenings.OK,sowhydoestheirbehavior
indicatemoreofaconcernwithhowmuchenergytheyexpendthanwithbeingexposedtopredators?No
onebelievesabeaverconsciouslyweighstheprosandconsofeachoftheseelements.Theanswerthat
somegiveisthattheirbehaviorhasevolvedovertime.It’sbeenshapedbyconstraintsovervaststretchesof
time,allofwhichcomesdowntothefactthatthebestforagingstrategyforbeaversisn’ttheonethatyields
themostfoodorwood.It’stheonethatresultsinthemostdescendants,themostoffspring.Solet’sdiscuss
howthisideaworks.
《生物学》
教授:好的,我们接着学习动物行为知识中动物如何做出决定的部分,今天我们将把重点放在
那些比较很艰难的决定上。动物,甚至包括昆虫在内,都似乎展示出一种非常复杂的决策过程。不
过,问题在于,这究竟是怎样一个过程呢?我的意思是,没有人真的会觉得,比如,一只蜜蜂会权衡
支持或者反对到那朵花上干活的各种因素。但是另一方面,问题在于动物如何解决那些复杂的、似
乎需要做出决定的问题。我们当然希望这些问题的答案能与自然选择拉上关系。比如,我们来看看
海狸的寻找食物有关的案例吧!海狸是素食类动物,主要吃植物。但同时他们又利用树木和树枝来建
造自己的住所,依靠树木高度远眺陆地来躲避它们的主要猎食者。所以,它们在寻找食物时会面临
很多选择。比如说,嗯,它们必须得知道那些树是它们应该推倒的。一些树木的营养价值高于其他,
一些树木更适合用来做建筑材料,而还有一些则两种用途都适合嗯,比如杨树。海狸们把杨树桩剥
皮为食,用杨树枝修筑居所。这样的话,杨树同时承担了两项任务。但是灰树,只被用作建材。另http://bailiedu.com
一个涉及到决定的问题是海狸们何时去找食。它们应该在较为温热的白天,它们更富精力之时去呢,
抑或是天气冷一些、捕食者更为活跃的晚上去?好的,还有两个更重要的问题;它们真的很关键,很
重要,记住了吧!
第一,我们假设当一棵大树有许多枝干,所以海狸能够从它身上获得的木材总量相当于三棵小
树,这时,海狸会如何选择?如果它选择那棵大树,它就必须把大树上的大块头木材扛回窝里去,但
把一大块木头移动40到50码是个不简单的活儿,会耗费大量的精力。但这项决定的好处是,它只
需要搬一次就能把木头搬到水里。不过,如果它选择了小树并且获得等量的木材呢,它把木头搬回
去时可以节省一些力气,但需要来来回回走三次。并且,从理论上说,它在住所之外的地方活动越
得多,就越有可能被捕食者发现。所以,哪一个选择更好呢?一棵大一些的树还是三棵小一些的树?
另一个关键问题与第一个树木大小问题有关,即它们会在距离水多远的地方获得木材?在大树提供较
多木头这一前提下,它们愿意走多远去找一棵大一些的树呢?海狸们如果需要杨树的话,它们当然需要比获得灰树走得更远。这种选择反映出了两种树木的相对价值。但木头的尺寸呢?它们会为了一棵
大树走得更远吗?
现在,我们当然会觉得如果树木越大,海狸为了获得这些树木的木材而进行远距离走动的意愿
也就越大。这的确能说通,是吧?假设你们要走一段较长的路的话,你们会选择一棵与这段距离价值
最为匹配的树木。但对于海狸而言,事实上,它们的选择恰恰与此相反。海狸只会推倒距水较近的