『新东方在线托福听力』为托福考生准备了ETS托福TPO/【学术讲座】#39听力练习，【学术讲座】#39原文答案解析，【学术讲座】#39听力原文练习音频翻译。

托福TPO/【学术讲座】#39听力原答案解析-音频翻译【新东方在线】

20世纪初，海獭——一种以海胆等无脊椎动物为食的海洋哺乳动物——因毛皮猎人的捕杀，在美国太平洋沿岸几乎灭绝。

In the early 1900s, sea otters, marine mammals that feed on invertebrates including sea urchins, were nearly wiped out along the United States Pacific Coast by fur hunters.

海獭消失后，海胆数量激增，破坏了海藻森林。

With otters gone, urchin numbers exploded, destroying kelp forests.

海藻是一种大型海草，正是海胆最喜爱的食物。

That kelp is a type of seaweed and it's sea urchins favorite food.

这导致无数海洋物种失去了海藻林提供的保护性栖息地。

This left countless marine species without the protective habitat that kelp forest provided to them.

随着海獭数量恢复，海胆数量下降，海藻林重新生长，生物多样性也再次繁荣。

As otters made a comeback, urchin numbers dropped, kelp forest grew back, and biodiversity flourished.

科学家由此意识到，海獭是一个关键物种——这类生物对生态系统的影响远超其种群数量比例。

Scientists realized otters were a keystone species, organisms whose impact on ecosystems is far greater than their numbers suggest.

类似的案例也发生在黄石国家公园。狼作为公园的顶级捕食者，曾被彻底消灭。

A similar case occurred in Yellowstone National Park. Wolves, the park's top predator, had been eradicated.

麋鹿（一种类似鹿的动物，也是狼最喜爱的猎物）数量因此激增，庞大的麋鹿群破坏了当地植被，包括公园曾闻名的柳树和山杨树。

Populations of elk, a deer-like animal and a favorite prey for wolves, soared and their huge populations damaged local vegetation, including the Willow and Aspen trees for which the park had been famous.

20世纪90年代，狼被重新引入公园以控制麋鹿数量。

In the 1990s, wolves were reintroduced to the park to get the elk population under control.

但狼不仅仅是减少了麋鹿的数量，它们还改变了麋鹿的行为模式。

But the wolves didn't just cut elk numbers, they changed elk behavior.

由于害怕被狼捕食，麋鹿开始避开溪流沿岸的区域——因为这些地方使它们尤其脆弱。

Afraid of being eaten by wolves, the elk avoided stream side areas where they're especially vulnerable.

这帮助柳树和山杨树在溪流边重新生长起来，而树木的恢复又带回了河狸——一种生活在溪流中、通过筑坝来为自己建造池塘的动物。

This helped Willow and Aspen trees reestablish themselves there, and the trees brought back Beavers, animals that live in streams and build dams to create ponds for themselves.

河狸筑起的水坝为鱼类、鸟类和两栖动物创造了栖息地——这是由另一个关键物种引发的巨大级联效应。

The Beaver dams created habitats for fish, birds and amphibians, a huge cascading effect because of this other keystone species.

What was the cause for the near disappearance of sea otters from waters along the United States Pacific coast?

According to the speaker, what happened to kelp forests when sea otters almost disappeared?

How did elk behavior change after wolves were reintroduced to Yellowstone National Park?

What does the speaker emphasize about beavers in Yellowstone?

Listen to a talk in a biology class.<br />In the early 1900s, sea otters, marine mammals that feed on invertebrates including sea urchins, were nearly wiped out along the United States Pacific Coast by fur hunters. With otters gone, urchin numbers exploded, destroying kelp forests. That kelp is a type of seaweed and it's sea urchins favorite food. This left countless marine species without the protective habitat that kelp forest provided to them. In 1972, hunting sea otters was banned. As otters made a comeback, urchin numbers dropped, kelp forest grew back, and biodiversity flourished. Scientists realized otters were a keystone species, organisms whose impact on ecosystems is far greater than their numbers suggest. A similar case occurred in Yellowstone National Park. Wolves, the parks top predator, had been eradicated. Populations of elk, a deer like animal and a favorite prey for wolves, soared and their huge populations damaged local vegetation, including the Willow and Aspen trees for which the park had been famous. In the 1990s, wolves were reintroduced to the park to get the elk population under control. But the wolves didn't just cut elk numbers, they changed elk behavior. Afraid of being eaten by wolves, the elk avoided stream side areas where they're especially vulnerable. This helped Willow and Aspen trees reestablish themselves there, and the trees brought back Beavers, animals that live in streams and build dams to create ponds for themselves. The Beaver dams created habitats for fish, birds and amphibians, a huge cascading effect because of this other keystone species.

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