考满分 toefl

1 .Listen to part of a lecture in a biology class.

听一段生物学课程中的演讲

1 .Professor, since we are going to talk about changes in animal populations in the wild, I'd like to ask about something I read in an article online, about how the population size of some animal species can affect other animal species, and how other environmental factors come into play too.

教授，因为我们将要谈论的是野生动物的种群变化，我想请教一下我在网上读到的一篇文章，关于某些动物物种的种群数量如何影响其他动物物种的种群数量，以及其他环境因素如何发挥作用。

1 .Right. Relationships between animal species in a given ecosystem can get pretty complex.

对。在一个给定的生态系统中的动物物种之间的关系是非常复杂的。

2 .Because in addition to predator-prey relationships, there are other variables that affect population size.

因为除了捕食与被捕食的关系，有其他一些变量影响种群数量。

1 .The article mentioned that populations of predators and their prey might go up rapidly and then decline all of a sudden.

文章提到，捕食者和猎物的种群数量可能会迅速增加，然后突然下降。

1 .Oh. Yeah! I read about that in my ecology class.

是的！我在生态学课上读到了一样的内容。

2 .It happens in cycles, I think that's called a boom-and-bust cycle. Right?

它周期发生。我认为这就是所谓的繁荣与衰退的周期。对吗？

1 .OK. Well, hold on a second.

行。好了，等一下。

2 .First I want to go over some key concepts.

首先，我想介绍一些关键概念。

3 .Let's say there was a species that had access to plenty of food and ideal conditions.

比方说，有一个物种能够获得充足的食物和理想的条件。

4 .Under those circumstances, its population would increase exponentially, meaning it would increase at an ever-accelerating pace.

在这种情况下，它的数量将成倍增加，这意味着它会以加速的方式增长。

1 .Wow! That sounds a little scary.

哇！这听起来有点吓人。

1 .Well, it doesn't usually happen.

嗯，这通常不会发生。

2 .Like you said, a rapid population growth is often followed by a sudden decline.

就像你说的，快速的增长往往紧跟着突然下降。

3 .But we do occasionally see exponential growth in nonnative species when they are transplanted into a new environment.

但我们偶尔也会看到外来物种被移植到一个新的环境时，他们以指数级增长。

4 .Because they face little competition and have favorable growing conditions.

嗯...因为他们面对的竞争小，具有良好的生长条件。

1 .But for most species, most of the time, resources are finite.

但对于大多数物种，大多数时候，资源是有限的。

2 .There's only so much available... which leads me to my point.

这里只有这么多可用的资源......这是我的观点的前提。

3 .Every ecosystem has what's called a carrying capacity.

每一个生态系统具有我们所说的承载能力。

4 .The carrying capacity is the maximum population size of a species that can be sustained by the resources of a particular ecosystem.

承载能力是一个特定的生态系统资源，可以支撑的最大种群数量。

5 .Resources are, of course, food, water, and just as important, space.

资源，指的是，食物，水，同样重要的是，空间。

1 .Although every species has a maximum rate at which the population of that species could increase, assuming ideal conditions for the species in its environment, there are always going to be environmental factors that limit population growth.

虽然每个物种都有该物种可以达到的最大增长速率，假设物种生存的条件是最理想化的。也总是有一些环境因素限制数量增长。

2 .This is called environmental resistance.

这就是所谓的环境阻力。

3 .Environmental resistance is important because it stops populations from growing out of control.

环境阻力是很重要的，因为它防止种群数量增长失控。

4 .Factors such as food supply, predation and disease affect population size, and can change from year to year or season to season.

一些因素例如食物供应，捕食者和疾病影响种群规模，并能每年或每季都在变化。

1 .OK. I think I get it.

好。我明白了。

1 .Well, let's look at a case study.

让我们来看一个案例研究，。

2 .That should make things clear.

会解释的比较清楚

3 .Some years ago, some of my colleagues conducted an experiment in an oak forest involving three different species: white-footed mice, gypsy moths and oak trees.

几年前，我的一些同事在橡树林做了一个实验，涉及三个不同的物种：白足鼠，舞毒蛾和橡树。

1 .OK. Now let me explain what the situation is in this forest.

现在让我来解释一下这片森林的状况。

2 .Oak trees produce acorns, and acorns are a primary food source for white-footed mice.

。橡树生产橡子，橡子是白足鼠的一种主要食物来源，

3 .Another food source for the white-footed mice is the gypsy moth.

白足鼠的另一种食物来源是舞毒蛾。

4 .So the size of the gypsy moth population is controlled by the white-footed mice, which is a good thing because gypsy moth caterpillars are considered pests.

因此，舞毒蛾种群的大小是由白足鼠控制的，这是一件好事，因为舞毒蛾幼虫被认为是害虫，

5 .They strip away the leaves from the oak trees every ten years or so.

他们能够每十年就剥光橡树的叶子。

1 .So the mice eat both acorns from the oak trees and gypsy moths...

因此，老鼠吃橡子和舞毒蛾。

2 .And the gypsy moth caterpillars eat oak tree leaves.

舞毒蛾幼虫吃橡树叶。

1 .Right. Now, what makes this set of relationships particularly interesting is that oak trees only produce a large number of acorns once every few years.

是的。现在，是什么让这组关系特别有趣的是，橡树能生产大量的橡子的年份特别有限。

1 .So during the years with fewer acorns, the white-footed mice have to deal with a smaller food supply.

所以在橡子少的年份，白足鼠不得不面对较少的食品供应。

1 .Yes. But in the years with large amounts of acorns, the mice have more food, which leads to...

是的。但在橡子多的年份中，白足鼠有更多的食物，从而导致...？

1 .The white-footed mice population growing.

白足鼠的数量增长。

1 .And the gypsy moth population decreasing.

舞毒蛾种群减少。

2 .How can we know that for sure? It seems like a big jump from more acorns to fewer gypsy moths.

为什么这么确定？这似乎是一个大的跳跃，从较多的橡子到较少的舞毒蛾。

1 .Well, we can know for sure because in this oak forest, the researchers decided to test the links between acorns and the two animal species.

好了，我们可以确定的是，在这片橡树林，研究人员决定测试橡子和两个动物物种之间的联系。

2 .In some parts of the forest, they had volunteers drop a large number of extra acorns on the forest floor.

在森林里的一些地方，他们让志愿者们在森林的地面上放了大量额外的橡子。

3 .And in another section of the forest, they removed a number of white-footed mice.

而在森林中的另一部分，他们弄走了一些白足鼠。

4 .In the forest areas where extra acorns had been dropped, the gypsy moth population soon went into a significant decline.

在放了额外的橡子的森林地区，舞毒蛾种群很快就显著下降。

5 .But in the section of the forest where the white-footed mice had been removed, the gypsy moth population exploded.

但在白足鼠被移走的区域，舞毒蛾种群的数量爆炸增长。