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旁白：听一段自然保护生物学的演讲。

Narrator: Listen to part of a lecture in a Conservation Biology class.

教授：全球变暖的一个后果就是灭绝。

Professor: One consequence of global warming is extinction.

有令人信服的证据表明，在这个世纪，全球变暖是许多植物和动物灭绝的驱动器。

There's compelling evidence that global warming will be a significant driver of many plant and animal extinctions in this century.

所以，我们在考虑可以帮助濒危物种度过这个史无前例的变暖趋势的策略。正如你所知道的，这个趋势是由燃烧矿物燃料而产生的温室气体造成的。

So we are considering various strategies to help some threatened species survive this unprecedented, this warming trend which, as you know, is caused mainly by greenhouse gases produced by the burning of fossil fuels.

呃……在自然保护生物学家中受到争议的最激进的策略就是辅助迁徙。

Um... the most radical strategy being debated among conservation biologists is Assisted Migration.

辅助迁徙就是在一个物种中挑选几个出来，将他们身体移动或者改变他们的位置。

Assisted migration means picking up members of a species, or members of a group of interdependent species and physically moving or translocating them.

嗯……例如，将濒临物种搬到更加凉爽的地方，搬到高纬度或者高海拔地区。

Um... translocating threatened species to a cooler place, to higher latitudes or higher elevations, for example.

Now, migration is a natural survival strategy.

在过去200万年中，较冷的冰河时期和较温暖的间冰期交替着。

Over the past two million years, colder glacial periods have alternated with warmer interglacial periods.

对这种渐变的天气，许多物种在好几百公里的范围之内迁徙。

And so, um, in response to these gradual climatic swings, some species have shifted their ranges hundreds of kilometers.

那么，你可能会想，为什么现在不让这种自然事件按自然发展进行？

So perhaps you are wondering why not let nature take its course now?

最主要的问题是当今碎片化的栖息地。

The main problem is today's fragmented habitats.

在上一次的间冰期，当冰川退下的时候，它们在它们身后留下了开阔的陆地。

During previous interglacial periods, when glaciers retreated, they left behind open land in their wakes.

现在，人类的发展覆盖了自然世界的很多地方。

Today human development has paved over much of the natural world.

房屋建设、高速公路和城市已经取代或者割穿了森林和草原。

Housing developments, highways and cities have replaced or sliced through forests and prairies.

在没有帮助的情况下，只剩下很少的地方让动物迁徙。

There are few corridors left for species to migrate through without help.

所以，自然资源保护者尝试着去尽可能地拯救更多的种群。

So conservationists are trying to save as many species as possible.

现在，辅助迁徙可以成为我们拯救策略中一个可行的部分，但是，有很多不确定性和风险。

Now, assisted migration could become a viable part of our rescue strategy, but there are a number of uncertainties and risks.

在没有更多研究的情况下，我们无法预测辅助迁徙对于每一个种群都可行。

Without more research, we can't predict if Assisted Migration will work for any given species.

例如，被重新安置的种群可能会因为缺乏食物而死去。

A translocated species could die out from lack of food, for example.

在另一个极端，我们可能成功地安置了这个物种，但是在5-10年内，这个物种可能会激增并且成为一个入侵物种。

At the other extreme, we might successfully translocate the species, but within five or ten years that species could proliferate and become an invasive species.

比如，一个非本地的植物通过独占土壤中的养分闭死了当地的植物。

Like a non-native plant that chokes out native plants by hogging the nutrients in the soil.

迁徙的动物也可能是入侵性的。

Translocated animals can become invasive too.

海蟾蜍在1935年被引进，用来控制破坏澳大利亚甘蔗种植园的害虫。

The cane toad was introduced back in 1935 to control an insect pest that was destroying Australia's sugarcane plantations.

但是在那片陆地上，海蟾蜍本身成为了一种害虫，并且破坏了很多野生动植物。

But the cane toad itself became a pest and has destroyed much of the wildlife on that continent.

有很多物种是互相依存的，和另外一个紧密联系。

Also, many species are interdependent, intimately connected to one another.

比如，一个动物吃某种特定的植物，而那个植物依赖着某种真菌去帮助它从土壤中获得养分，也需要某种昆虫帮它授粉。

Like animals that eat a certain plant and that plant relies on a certain fungus to help it get nutrients from soil and on a certain insect for pollination.

我们可能需要将整个物种网络迁徙，并且很难知道在哪里划定最后界限。

We probably have to translocate entire networks of species and it's hard to know where to draw the line.

在此之外，就此而言，辅助迁徙或者任何迁徙至少可以帮助一些物种的这一点还不是很明确。

And in addition to all that, it is not even clear that assisted migration or any migration for that matter, will help at least for some species.

当我们开始燃烧燃料的时候，地球已经处在它一个温暖的间冰期了。

Earth was already in one of its warm interglacial periods when we started burning fossil fuels.

而在这个21世纪，全球温度有望升高2-6度。

And in the twenty-first century, global temperatures are expected to rise two to six degrees.

加热的速率比上一次冰川消退的时候要大的多，大约12,000年前。

That rate of heating is far greater than during the last glacial retreat some 12,000 years ago.

呃……是否使用辅助迁徙，这个争论主要是在生物群落中。

Um ... whether to use Assisted Migration, this debate is mostly within the biology community right now.

但是最终的决策者，至少在美国，会是管理自然资源的政府机构。

But the ultimate decision-makers, in the United States at least, will be the government agencies that manage natural resources.

辅助机构确实需要这个层面的监督。

Assisted Migration really needs this level of oversight, and soon.

现在，没有关于使用辅助迁徙的国家政策去帮助物种在气候变化下存活。

Currently there's no public policy on using assisted migration to help species survive climate change.

只要不是害虫，人们不需要获得许可去移动植物或者无脊椎动物。

People aren't even required to seek permits to move plants or invertebrate animals around as long as they are not classified as pests.

有一个例子，一群自然资源保护论者，已经试图通过他们自己的尝试，通过辅助迁徙，去拯救濒危的树木，佛罗里达香榧树。

In one case, a group of conservationists has already taken it upon itself to try on their own to save an endangered tree, the Florida Torreya tree, through Assisted Migration.

大约只有1000课佛罗里达香榧树剩下。

There's only about a thousand individual Florida Torreys left.

并且全球变暖预计会大大减少这种树木的栖息地。

And global warming is expected to significantly reduce or eliminate this tree's habitat.

所以，这些保护团体想要将籽苗，佛罗里达香榧树籽苗向北转移500公里，为了扩张物种范围。

So this conservation group wants to translocate seedlings, Florida Torreyas seedlings, 500 kilometers north in order to expand the species' range.

这个团体认为这个方法是正当的，但是我和其他一些生物学家会紧密关注这群持不同意见的人是怎么操作的，因为，就像我说的，可能会有意想不到的后果。

The group believed its effort is justified, but I and many other biologists will be watching very closely how this maverick group makes out, because like I said, there could be unintended consequences.

According to the professor, what problem is assisted migration intended to overcome?

What point does the professor make when she discusses the cane toad?

What does the professor imply when she mentions translocating networks of species?

What does the professor imply about the government's role in regulating assisted migration in the United States?

What is the professor's attitude toward the effort to save the Florida torreya?

Narrator 
Listen to part of a lecture in a Conservation Biology class. 
Professor 
One consequence of global warming is extinction. There's compelling evidence that global warming will be a significant driver of many plant and animal extinctions in this century. So we are considering various strategies to help some threatened species survive this unprecedented, this warming trend which, as you know, is caused mainly by greenhouse gases produced by the burning of fossil fuels. 
Um... the most radical strategy being debated among conservation biologists is Assisted Migration. 
Assisted migration means picking up members of a species, or members of a group of interdependent species and physically moving or translocating them. Um... translocating threatened species to a cooler place, to higher latitudes or higher elevations, for example. Now, migration is a natural survival strategy. Over the past two million years, colder glacial periods have alternated with warmer interglacial periods. And so, um, in response to these gradual climatic swings, some species have shifted their ranges hundreds of kilometers. 
So perhaps you are wondering why not let nature take its course now? Well, we can't. The main problem is today's fragmented habitats. During previous interglacial periods, when glaciers retreated, they left behind open land in their wakes. Today human development has paved over much of the natural world. Ecosystems are fragmented. Housing developments, highways and cities have replaced or sliced through forests and prairies. There are a few quarters left for species to migrate through without help. So conservationists are trying to save as many species as possible. 
Now, assisted migration could become a viable part of our rescue strategy, but there are a number of uncertainties and risks. Without more research, we can't predict if Assisted Migration will work for any given species. A translocated species could die out from lack of food, for example. At the other extreme, we might successfully translocate the species, but within five or ten years that species could proliferate and become an invasive species. Like a non-native plant that chokes out native plants by hogging the nutrients in the soil. Translocated animals can become invasive too. It happened in Australia. The cane toad was introduced back in 1935 to control an insect pest that was destroying Australia's sugarcane plantations. But the cane toad itself became a pest and has destroyed much of the wildlife on that continent. 
Also, many species are interdependent, intimately connected to one another. Like animals that eat a certain plant and that plant relies on a certain fungus to help it get nutrients from soil and on a certain insect for pollination. We probably have to translocate entire networks of species and it's hard to know where to draw the line. 
And in addition to all that, it is not even clear that assisted migration or any migration for that matter, will help at least for some species. Earth was already in one of its warm interglacial periods when we started burning fossil fuels. And in the twenty-first century, global temperatures are expected to rise two to six degrees. That rate of heating is far greater than during the last glacial retreat some 12,000 years ago. 
Um ... whether to use Assisted Migration, this debate is mostly within the biology community right now. But the ultimate decision-makers, in the United States at least, will be the government agencies that manage natural resources. Assisted Migration really needs this level of oversight, and soon. Currently there's no public policy on using assisted migration to help species survive climate change. People aren't even required to seek permits to move plants or invertebrate animals 
around as long as they are not classified as pests. In one case, a group of conservationists has already taken it upon itself to try on their own to save an endangered tree, the Florida Torreya tree, through Assisted Migration. 
There's only about a thousand individual Florida Torrey as left. And global warming is expected to significantly reduce or eliminate this tree's habitat. So this conservation group wants to translocate seedlings, Florida Torreya seedlings, 500 kilometers north in order to expand the species' range. The group believed its effort is justified, but I and many other biologists will be watching very closely how this maverick group makes out, because like I said, there could be unintended consequences.