考满分 toefl

1 .<-NARRATOR:->Listen to part of a lecture in a biology class.

旁白：听一段生物学课程。

1 .<-MALE STUDENT:->Professor, since we're 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.

学生：教授，既然我们讨论动物种群在自然界的变化，我想问一些关于我在网上读到的文章，一些物种的群体大小是如何影响其他物种的，而且其他环境因素是如何发挥作用的。

1 .<-FEMALE PROFESSOR:->Right, relationships between animal species in a given ecosystem can get pretty complex.

教授：好的。物种关系在特定的生态系统中可能会非常的复杂。

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

因为除了生物掠夺关系，还有其他影响种群大小的变数。

1 .<-MALE STUDENT:->[sort of quizzically] The article mentioned that populations of predators and their prey might go up rapidly and then decline all of a sudden.

学生：文章提到捕食者的数量和它们的猎物可能很快地上升，然后突然下降。

1 .<-FEMALE STUDENT:->[chiming in] Oh, yeah, I read about that in my ecology class. It happens in cycles.

学生：是的！我在生态学课上读到过，它会周期性地出现。

2 .I think that's called a boom-and-bust cycle, right?

我想这叫做繁荣与萧条交替循环，对吗？

1 .<-FEMALE PROFESSOR:->Ok, well … hold on a second.

教授：好的，稍等。

2 .First, I want to go over some key concepts-let's say there was a species that had access to plenty of food and ideal conditions-under those circumstances its population would increase exponentially,meaning it would increase at an ever-accelerating pace.

首先我想复习一些关键概念—比如说有一个物种可以获得很多食物并存在于理想的环境中—在这样的环境下，它的种群会迅猛增长，意味着它将以持续加速的速度增长。

1 .<-MALE STUDENT:->Wow-that sounds a little scary.

学生：哇！听起来有点可怕。

1 .<-FEMALE PROFESSOR:->Well, it doesn't usually happen. Like you said, a rapid population growth is often followed by a sudden decline.

教授：这通常不会发生，如你所说，一个快速增长的种群随之而来的经常是突然衰退。

2 .But we do occasionally see exponential growth in nonnative species when they are transplanted into a new environment-um, because they face little competition and have favorable growing conditions.

但是我们偶尔会看到当非本地的物种转移到新环境时，它们会急剧增长。因为它们不用面对竞争，并且有良好的生长条件。

3 .But for most species, most of the time,resources are finite-there's only so much available-which leads me to my point ….

但对于多数物种来说，更多时候资源有限，只有一些可以利用，这将引出我要说的重点。

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

每个生态系统都有我们所说的容纳量。

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

容纳量是物种群体大小的最大化，可以由一个特定生态系统的资源支撑。

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

资源当然是食物、水和同等重要的空间。

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're always going to be environmental factors that limit population growth.

假设物种处于理想环境，尽管每个物种都有它种群增长的最大定额，总会有环境因素限制种群增长。

2 .This is called environmental resistance.

这叫做环境阻力。

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

环境阻力很重要，因为它阻止种群增长失控。

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

如食物供给、捕食和疾病等因素可以影响种群大小，而且年年或每季都有变化。

1 .<-MALE STUDENT:->OK, I think I get it.

学生：好的，我想我明白了。

1 .<-FEMALE PROFESSOR:->Well, let's look at a case study-that should make things clear.

教授：让我们看一个个案研究，这会让事情看起来更简单。

2 .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，我的一些同事在栎树橡木林进行一项实验，其中包括三种不同的物种：白足鼠、舞毒蛾和橡树。

1 .OK, uh, now let me explain what the situation is in this forest.

好的，让我解释一下这个森林里的情况。

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

橡树产生橡实，而橡实是白足鼠主要的食物来源。

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

白足鼠的另一个食物来源是舞毒蛾。

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.

所以舞毒蛾的物种大小受到白足鼠的控制，这是一件好事，因为舞毒蛾的毛虫被认为是害虫。

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

每十年左右，它们会剥去橡树的叶子。

1 .<-MALE STUDENT:->So the mice eat both acorns from the oak trees and gypsy moths … and the gypsy moth caterpillars eat oak tree leaves.

学生：所以鼠吃橡树上的橡实和舞毒蛾，而舞毒蛾的毛虫吃像树叶。

1 .<-FEMALE PROFESSOR:->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.

教授：是的。现在使这一套关系特别有趣的是只有每隔几年橡树才会产出一次大量的橡实。

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

学生：所以在橡实很少的年份里，白足鼠不得不应对食物供应不足的状况。

1 .<-FEMALE PROFESSOR:->Yes. But in the years with large amounts of acorns … the mice have more food which leads to-

教授：是的，但是在有大量橡实的年份里，鼠会有更多的食物，这会导致......

1 .<-MALE STUDENT:->The white-footed mouse population growing-

学生：白足鼠的种群壮大。

1 .<-FEMALE PROFESSOR:->And the gypsy moth population decreasing.

教授：而且舞毒蛾的种群会下降。

1 .<-MALE STUDENT:->How can we know that for sure? It seems like a big jump from more acorns to fewer gypsy moths.

学生：我们怎么能确定？从更多的橡实到舞毒蛾的减少，中间似乎有着大步飞跃。

1 .<-FEMALE PROFESSOR:->Well, we can know for sure because in this oak forest, the researchers decided to test the links between acorns and the two animals species.

教授：我们可以确定，因为在栎树橡木林里，研究者决定测试橡实和两个物种的联系。

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

在森林的一些部分，他们让志愿者将大量橡实放在地上。

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

在森林的另一个地方，他们移走了许多白足鼠。

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

在放上额外的橡实的森林地带，舞毒蛾的种群不久就大幅下降。

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

但是在移走白足鼠的森林地带，舞毒蛾的种群暴涨。