考满分 toefl

1 .Listen to part of a lectures in an animal behavior class.

听一段动物行为课上的演讲

1 .P: OK, yesterday, we talked about how the different behaviors help animals adapt in response to competitors. We looked at how moving to another location and becoming geographically isolated from other members of the species often explains how a group of animals eventually evolves into a different species. Now, what do we call this process? Dan?

教授：好的，昨天，我们讨论了不同的行为是如何帮助动物针对竞争对手做出适应的。我们研究了迁移到另一个地方并在地理上与该物种的其他成员隔离开来，通常是如何解释一群动物最终进化成一个不同物种的。那么，我们把这个过程叫做什么呢？丹？

2 .S: Speciation. P: Good, speciation. Explain what we said about that, OK? S: Eventually, the isolated group becomes a distinct species that will no longer interbreed with members of the species it became isolated from.

学生：物种形成。 教授：很好，物种形成。解释一下我们对此的阐述，好吗？ 学生：最终，被隔离的群体变成一个独特的物种，它将不再与它所隔离的那个物种的成员进行杂交繁殖。

1 .P: Exactly. Now, some scientists argue that speciation can only occur if there's a geographical barrier, that behavioral differences alone won't cause two groups of animals to become two different species over time, and it's true that it can be hard to prove that behavioral differences are the cause of speciation. I mean, if a small group of animals starts behaving differently from the larger group, they might physically isolate themselves, move to another location. So we could argue that it was the geography that actually caused the speciation.

教授：完全正确。现在，一些科学家认为，只有当存在地理障碍时物种形成才会发生，仅靠行为差异不会随着时间的推移导致两组动物变成两个不同的物种，而且确实很难证明行为差异是物种形成的原因。我的意思是，如果一小群动物开始表现得与大群体不同，它们可能会在物理上使自己隔离，迁移到另一个地方。所以我们可以说实际上是地理因素导致了物种形成。

2 .But to limit ourselves to only one possible explanation for speciation, it's a bit of an oversimplification. There are many complicated reasons species evolve. Let's look at an example where speciation due to behavioral differences might be happening. We're going to talk about killer whales, specifically killer whales found off the western coast of Canada.

但是，仅仅局限于对物种形成的一种可能解释，这有点过于简单化了。物种进化有许多复杂的原因。让我们来看一个例子，在这个例子中可能正在发生因行为差异导致的物种形成。我们要讨论的是虎鲸，具体来说是在加拿大西海岸发现的虎鲸。

3 .Researchers have found that in this region, the species has divided behaviorally into two separate types that don't interact. They call these two types: transients and residents. Transients move a much greater distance along the Pacific Coast looking for food than residents do. Residents, as their name suggests, live in one general location. Resident killer whales eat fish such as salmon, but transients eat seals.

研究人员发现，在这个地区，该物种在行为上已经分化成两种互不交流的不同类型。他们把这两种类型称为：“过客型” 和 “居留型”。“过客型” 虎鲸沿着太平洋海岸寻找食物时移动的距离比 “居留型” 虎鲸远得多。“居留型”，正如其名字所暗示的，生活在一个大致固定的地方。“居留型” 虎鲸吃鱼，比如鲑鱼，而 “过客型” 虎鲸吃海豹。

4 .Now, let's assume that transients and residents both developed from a single kind of killer whale that had one specialized diet, whichever diet that was, fish or seal, the whales were all competing for that food. It's easy to imagine that if competition for that food got tough, any members of the species who evolved an ability to live on alternative food sources would improve their chances for survival. That's what we think might've happened here.

现在，让我们假设 “过客型” 和 “居留型” 虎鲸都源自一种有着单一特殊食物偏好的虎鲸，不管那种食物是鱼还是海豹，这些虎鲸都在竞争那种食物。很容易想象，如果对那种食物的竞争变得激烈，这个物种中任何进化出以其他食物来源生存能力的成员都将提高它们的生存几率。我们认为这里可能就发生了这样的情况。

5 .But it's the diet of their prey that I want you to consider now. Seals and salmon both have basically the same diet. They feed on smaller fish. Let's look at this chart. This chart represents a food web, a possible model for how residents and transients interact. There are still some unknowns, but the layout here is a logical guess based on what we know about the diets of the animals involved. So even if the residents and transients don't directly interact with each other, their prey share the same diet, so there is still a connection there.

但现在我希望你们考虑一下它们猎物的食物。海豹和鲑鱼基本上有着相同的食物。它们以较小的鱼为食。让我们看看这个图表。这个图表代表了一个食物网，一个关于 “居留型” 和 “过客型” 虎鲸如何相互作用的可能模型。仍然存在一些未知因素，但这里的布局是基于我们对相关动物饮食的了解所做出的合理猜测。所以，即使 “居留型” 和 “过客型” 虎鲸不直接相互作用，它们的猎物有着相同的食物，所以在这方面仍然存在着一种联系。

6 .S: But I don't understand if the seals and salmon are directly competing for the same food, isn't that going to have a negative effect on all the animals involved?

学生：但是我不明白，如果海豹和鲑鱼直接在竞争相同的食物，这难道不会对所有相关的动物产生负面影响吗？

7 .P: That's a good question. Think about it, by eating salmon, resident killer whales reduce competition for smaller fish. Without as many salmon eating the smaller fish, the seals have more food, so the seal population increases. Then the transient whales benefit because they have more seals to eat. But the reverse is also true. When the transients eat more seals, there are more fish for the salmon, so the residents have more salmon to eat.

教授：这是个好问题。想一想，“居留型” 虎鲸通过吃鲑鱼，减少了对较小鱼类的竞争。没有那么多鲑鱼吃较小的鱼，海豹就有了更多的食物，所以海豹的数量增加了。然后 “过客型” 虎鲸就受益了，因为它们有更多的海豹可吃。但反过来也是如此。当 “过客型” 虎鲸吃了更多的海豹，就有更多的鱼留给鲑鱼，所以 “居留型” 虎鲸就有更多的鲑鱼可吃。

8 .Now, we've noticed other behavioral differences among these two types of killer whales. For instance, residents usually travel in much larger groups than transients. Any ideas why?

现在，我们还注意到这两种类型的虎鲸之间的其他行为差异。例如，“居留型” 虎鲸通常比 “过客型” 虎鲸以大得多的群体游动。有人知道为什么吗？

9 .S: Well, I guess seals are probably harder to catch than salmon. P: OK...

学生：嗯，我猜海豹可能比鲑鱼更难捕捉。 教授：好的……

10 .S: I mean, if seals know that the transients are around, they could just go on land for a little while, right? So maybe a smaller group of transient whales are less likely to be noticed by the seals, but the residents, they don't have to avoid notice by staying in small groups, because, well, salmon probably don't have much chance of escaping them anyway.

学生：我的意思是，如果海豹知道 “过客型” 虎鲸在附近，它们可以暂时上岸，对吧？所以也许一小群 “过客型” 虎鲸不太容易被海豹注意到，但是 “居留型” 虎鲸不必为了不被注意而保持小群体，因为，嗯，鲑鱼反正可能也没什么机会从它们那里逃脱。

11 .P: Right. It's important to understand the relationships in this food web because the resident killer whale population in the area we've been discussing is now listed as endangered. And knowing how resident killer whales interact with their environment and the other killer whales around them will provide valuable insights into how to save the resident killer whales.

教授：对的。理解这个食物网中的关系是很重要的，因为我们一直在讨论的这个地区的 “居留型” 虎鲸种群现在被列为濒危物种。了解 “居留型” 虎鲸如何与它们的环境以及周围其他虎鲸相互作用，将为如何拯救 “居留型” 虎鲸提供有价值的见解。