Foraging Behavior Among Beavers托福听力原文翻译及问题答案

Foraging Behavior Among Beavers托福听力原文翻译及问题答案

一、Foraging Behavior Among Beavers托福听力原文：

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…how 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托福听力中文翻译：

旁白：在生物课上听一节课的一部分。

女教授：好的，让我们继续讨论动物行为，谈谈动物面临的决定……复杂的决定。动物，甚至昆虫，执行看起来非常复杂的决策过程。问题是怎么做？我的意思是，没有人真的这么认为，比如说，一只蜜蜂会权衡为这朵花或那朵花授粉的利弊。但是，动物如何解决复杂的问题，这些问题似乎需要做出决策？

当然，我们将提出的答案是，它们的行为在很大程度上是自然选择的问题。作为一个例子，让我们看看海狸的觅食行为。海狸吃植物，主要是树木。他们还利用树木和树枝在溪流和湖泊中建造家园。因此，当它们寻找食物和庇护所材料时，它们必须离开家园，登上陆地，那里是它们的主要捕食者。因此，在觅食方面必须做出许多选择。例如，呃，他们需要决定应该砍伐什么样的树。有些树的营养价值比其他树高，有些树更适合做建筑材料。有些对两者都有好处：嗯，白杨树。海狸剥下树皮来吃，它们也用树枝搭建庇护所。所以白杨有双重职责。但白蜡树：海狸只将白蜡树用于建筑。另一个决定是什么时候觅食。它们应该在白天外出，当外面更热时，它们必须消耗更多的能量，还是在晚上，当天气凉爽时，捕食者更活跃？

好的，但还有两个更重要的问题，实际上是最核心、最重要的。好啊首先，假设一只海狸可以从一棵有很多树枝的大树上获得与从三棵小树上获得的木材相同数量的木材。它应该选择哪一个？如果它选择了一棵大树，就必须把那块大木头扛回家。拖着一块40或50码的大木头是一项艰苦的工作；需要很多能量。当然，它只需要一次就可以把木头放回水中。

另一方面，如果换成三棵小树，每棵树需要更少的能量才能将木材运回家，但这三棵树需要来回三次。据推测，它离开家的频率越高，就越容易受到捕食者的袭击。那么哪一个更好：一棵大树还是三棵小树？另一个关键问题，它与第一个、大小问题有关，是……它应该离水多远才能长出树木？它应该愿意为一棵大树走更远的路吗，因为它会从中获得这么多木材？海狸为了得到一棵白杨树而不是一棵白蜡树，当然离水更远。这反映了它们的相对价值。但是尺寸呢？对于一棵大树，它会比一棵小树走得更远吗？现在，我会想，树越大，海狸愿意为它游得越远。这是有道理的，对吗？如果你要远行，带回来尽可能多的木材，让旅行值得。但实际上，情况恰恰相反。海狸只会砍伐靠近水面的大树。他们会远行，只为了砍倒一些小树，这些小树可以很快砍倒，然后很快就拖回家。

一般来说，它们离水越远，砍倒的树就越小。他们愿意进行更多的旅行，以运回更少的木材，这将带来更大的风险暴露于捕食者。因此，看起来海狸对尽量减少与捕食者的接触不那么感兴趣，而更感兴趣的是在觅食木材时节约能源。这也可以解释为什么海狸主要在晚上觅食。

好吧，那么，为什么它们的行为更关心它们消耗了多少能量，而不是暴露在捕食者面前？没有人相信海狸会有意识地权衡这些因素的利弊。一些人给出的答案是，它们的行为随着时间的推移而演变：它是由长时间的限制因素塑造的，所有这些都归结为一个事实，即海狸的最佳觅食策略不是产生最多食物或木材的策略：而是产生最多后代、最多后代的策略。让我们来讨论一下这个想法是如何运作的。

三、Foraging Behavior Among Beavers托福听力问题：

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托福听力答案：

A1:正确答案：D

A2:正确答案：D

A3:正确答案：AC

A4:正确答案：B

A5:正确答案：B

A6:正确答案：A