Foraging Behavior Among Beavers托福聽力原文翻譯及問題答案

Foraging Behavior Among Beavers托福聽力原文翻譯及問題答案

一、Foraging Behavior Among Beavers托福聽力原文：

Narrator:Listen to part of a lecture in a biology class.

Female Professor:OK,let's continue our discussion about animal behavior by talking about decisions that animals face…complex ones.Animals,even insects,carry out what look like very complex decision-making processes.The question is how?I mean,no one really thinks that—say,a bee—goes through weighing the pros and cons of pollinating this flower,or that flower.But then how do animals solve complex questions,questions that seem to require decision making?

The answer we'll propose,of course,is that their behavior is largely a matter of natural selection.As an example let’s look at foraging behavior among beavers.Beavers eat plants,mostly trees.And they also use trees and tree branches to construct their homes in streams and lakes.So when they do forage for food and for shelter materials,they have to leave their homes and go up on land,where their main predators are.So there are a number of choices that have to be made about foraging.So,for example,uh,they need to decide what kind of tree they should cut down.Some trees have higher nutritional value than others,and some are better for building material.And some are good for both:um,aspen trees.Beavers peel off the bark to eat,and they also use the branches for building their shelters.So aspens do double duty.But ash trees:beavers use ash trees only for construction.Another decision is when to forage for food.Should they go out during the daytime,when it's hotter outside and they have to expend more energy,or at night,when the weather’s cooler but predators are more active?

OK,but there are two more important issues—really the most central,the most,uh,important.OK?First,let's say a beaver could get the same amount of wood from a single large tree—one that has lots of branches—as it could get from three small trees.Which should it choose?If it chooses one large tree,it'll have to carry that large piece of wood back home.And lugging a big piece of wood 40 or 50 yards is hard work;takes a lot of energy.Of course,it'll have to make only one trip to get the wood back to the water.

On the other hand,if it goes for three small trees instead,it'll take less energy per tree to get the wood back home,but it'll have to make three trips back and forth for the three trees.And presumably,the more often it wanders from home,the more it’s likely to be exposed to predators.So which is better:a single large tree or three small trees?Another critical issue,and it’s related to,to the first,to the size issue,is…h(huán)ow far from the water should it go to get trees?Should it be willing to travel a greater distance for a large tree,since it’ll get so much wood from it?Beavers certainly go farther from the water to get an aspen tree than for an ash tree.That reflects their relative values.But what about size?Will it travel farther for a larger tree than it will for a smaller tree?Now,I would’ve thought,the bigger the tree,the farther the beaver would be willing to travel for it.That’d make sense,right?If you’re going to travel far,make the trip worth it by bringing back the most wood possible.But actually,the opposite is true.Beavers will cut down only large trees that’re close to the water.They’ll travel far only to cut down certain small trees that they can cut down quickly and drag back home quickly.

Generally,the farther they go from the water,the smaller the tree they'll cut down.They're willing to make more trips to haul back less wood,which carries a greater risk of being exposed to predators.So it looks as though beavers are less interested in minimizing their exposure to predators and more interested in saving energy when foraging for wood.Which may also explain why beavers forage primarily during the evenings.

OK,so why does their behavior indicate more of a concern with how much energy they expend than with being exposed to predators?No one believes a beaver consciously weighs the pros and cons of each of these elements.The answer that some give is that their behavior has evolved over time:it's been shaped by constraints over vast stretches of time,all of which comes down to the fact that the best foraging strategy for beavers isn't the one that yields the most food or wood:it's the one that results in the most descendants,the most offspring.So let's discuss how this idea works.

二、Foraging Behavior Among Beavers托福聽力中文翻譯：

旁白：在生物課上聽一節(jié)課的一部分。

女教授：好的，讓我們繼續(xù)討論動物行為，談談動物面臨的決定……復雜的決定。動物，甚至昆蟲，執(zhí)行看起來非常復雜的決策過程。問題是怎么做？我的意思是，沒有人真的這么認為，比如說，一只蜜蜂會權衡為這朵花或那朵花授粉的利弊。但是，動物如何解決復雜的問題，這些問題似乎需要做出決策？

當然，我們將提出的答案是，它們的行為在很大程度上是自然選擇的問題。作為一個例子，讓我們看看海貍的覓食行為。海貍吃植物，主要是樹木。他們還利用樹木和樹枝在溪流和湖泊中建造家園。因此，當它們尋找食物和庇護所材料時，它們必須離開家園，登上陸地，那里是它們的主要捕食者。因此，在覓食方面必須做出許多選擇。例如，呃，他們需要決定應該砍伐什么樣的樹。有些樹的營養(yǎng)價值比其他樹高，有些樹更適合做建筑材料。有些對兩者都有好處：嗯，白楊樹。海貍剝下樹皮來吃，它們也用樹枝搭建庇護所。所以白楊有雙重職責。但白蠟樹：海貍只將白蠟樹用于建筑。另一個決定是什么時候覓食。它們應該在白天外出，當外面更熱時，它們必須消耗更多的能量，還是在晚上，當天氣涼爽時，捕食者更活躍？

好的，但還有兩個更重要的問題，實際上是最核心、最重要的。好啊首先，假設一只海貍可以從一棵有很多樹枝的大樹上獲得與從三棵小樹上獲得的木材相同數(shù)量的木材。它應該選擇哪一個？如果它選擇了一棵大樹，就必須把那塊大木頭扛回家。拖著一塊40或50碼的大木頭是一項艱苦的工作；需要很多能量。當然，它只需要一次就可以把木頭放回水中。

另一方面，如果換成三棵小樹，每棵樹需要更少的能量才能將木材運回家，但這三棵樹需要來回三次。據(jù)推測，它離開家的頻率越高，就越容易受到捕食者的襲擊。那么哪一個更好：一棵大樹還是三棵小樹？另一個關鍵問題，它與第一個、大小問題有關，是……它應該離水多遠才能長出樹木？它應該愿意為一棵大樹走更遠的路嗎，因為它會從中獲得這么多木材？海貍為了得到一棵白楊樹而不是一棵白蠟樹，當然離水更遠。這反映了它們的相對價值。但是尺寸呢？對于一棵大樹，它會比一棵小樹走得更遠嗎？現(xiàn)在，我會想，樹越大，海貍愿意為它游得越遠。這是有道理的，對嗎？如果你要遠行，帶回來盡可能多的木材，讓旅行值得。但實際上，情況恰恰相反。海貍只會砍伐靠近水面的大樹。他們會遠行，只為了砍倒一些小樹，這些小樹可以很快砍倒，然后很快就拖回家。

一般來說，它們離水越遠，砍倒的樹就越小。他們愿意進行更多的旅行，以運回更少的木材，這將帶來更大的風險暴露于捕食者。因此，看起來海貍對盡量減少與捕食者的接觸不那么感興趣，而更感興趣的是在覓食木材時節(jié)約能源。這也可以解釋為什么海貍主要在晚上覓食。

好吧，那么，為什么它們的行為更關心它們消耗了多少能量，而不是暴露在捕食者面前？沒有人相信海貍會有意識地權衡這些因素的利弊。一些人給出的答案是，它們的行為隨著時間的推移而演變：它是由長時間的限制因素塑造的，所有這些都歸結為一個事實，即海貍的最佳覓食策略不是產(chǎn)生最多食物或木材的策略：而是產(chǎn)生最多后代、最多后代的策略。讓我們來討論一下這個想法是如何運作的。

三、Foraging Behavior Among Beavers托福聽力問題：

Q1:1.What is the lecture mainly about?

A.Different foraging strategies among animals

B.Methods beavers use to gather building materials

C.Decisions beavers make about where to live

D.Choices beavers face when foraging

Q2:2.What difference between aspen trees and ash trees does the professor point out?

A.Aspen trees are easier to transport.

B.Aspen trees provide better wood for construction.

C.Aspen trees provide less nutrition for beavers.

D.Aspen trees have more overall value to beavers.

Q3:3.What does the professor identify as the two central issues involved in beavers foraging behavior?[Click on 2 answers.]

A.How far from home to forage

B.How to cope with competition

C.What size tree to cut down

D.What time of year material for construction is available

Q4:4.What does the professor say about the cutting down of large trees?

A.Beavers generally prefer cutting down large trees to small trees.

B.Beavers generally do not travel long distances to cut down large trees.

C.Beavers will not cut down large trees of certain species.

D.Beavers use large trees mainly for the purpose of building shelters.

Q5:5.According to the professor,why do beavers generally forage at night?

A.Beavers are safer from predators if they forage at night.

B.Foraging at night requires less energy than foraging in the daytime.

C.Beavers stay with their offspring during the daytime.

D.Beavers face less competition for food from other animals during the night.

Q6:6.Why does the professor say this:If you’re going to travel far,make the trip worth it by bringing back the most wood possible.

A.To explain her reasoning.

B.To indicate why her belief was wrong.

C.To give an example of a decision beavers make.

D.To explain the reason beavers travel far for wood.

四、Foraging Behavior Among Beavers托福聽力答案：

A1:正確答案：D

A2:正確答案：D

A3:正確答案：AC

A4:正確答案：B

A5:正確答案：B

A6:正確答案：A

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