模拟测试卷4-2019-8月新卷 Why does a student mention the introduction of shrimp into a lake in Montana?

[00:00.00]Narrator:Listen to part of a lecture in an ecology class.[00:07.75]Professor:So we’ve been looking at threats to the survival of many species of plants and animals all over the world. Two threats that we’ve identified are climate change and habitat destruction.[00:20.58] So now the question is what can be done to save these species? Stephanie?[00:25.64]Stephanie:Well, we can stop burning fossil fuels. You know, use solar or wind energy. [00:32.50]Male:I heard about the seed banks all over the world. Scientists are collecting seeds from all kinds of plants so they don’t become extinct and they’re also breeding threatened animals. Of course, that probably means in zoos.[00:49.15]Professor:Okay. These are definitely approaches being used. But there’s another alternative that more and more conservationists and ecologists are looking at. [00:59.71]It’s called assisted migration. Assisted migration is the process of physically moving an entire species from a habitat where they are endangered to a new habitat that’s more hospitable.[01:12.81]Stephanie:But you know, that reminds of me that species of shrimp you told us about before, the one that wildlife managers introduced into a lake in Montana because they thought it would be suitable food for some of the lake’s fish? [01:27.30]But the shrimp became invasive. It ended up competing with the fish for its food and disrupting the entire lake’s food web.[01:36.73]Professor:Yes, and sometimes the species will occupy a wider area than intended. And it’s because of risks like these that this is a very controversial idea.[01:48.54]Male:Has it ever been done successfully? [01:51.47]Professor:It seems so. In the late 1990s, with populations of two butterfly species in England, climate data had shown that the butterfly’s habitat was experiencing warmer temperatures, which was directly affecting their ability to reproduce so conservationists used computer climate models to locate areas that could provide a more suitable habitat.[02:17.72] First, one species was moved about 35 kilometers north, and the following year, the other species was moved about 65 kilometers north. [02:28.68]And for over 20 years, both species had been followed very closely. So far anyway, we haven’t seen any negative consequences.[02:38.44]Stephanie:Wow. But how do you decide which species to move and where to move them? [02:44.96]Professor:Well, researchers have come up with a set of criteria. First of all, only species that are at a high risk of extinction because of climate change, or habitat destruction are even considered.[02:58.99] And obviously there’d have to be a suitable place to reestablish the species. But mostly importantly, the benefits of relocation would have to outweigh the biological cost.[03:11.80] However, the problem with this criterion is that we don’t see the biological costs until the damage has been done, as in the case of the shrimp.[03:21.89]So okay, let’s see how well one animal, the Iberian desman, fits these criteria. The Iberian desman is a semi-aquatic animal that lives among fast-flowing streams in the Pyrenees Mountains of southern France and northern Spain.[03:38.49] Researchers considered the Iberian desman a good candidate for relocation for two reasons. First, it’s found in only in a very limited area. This suggests that for whatever reason, they can’t easily migrate to a new habitat on their own.[03:56.09] Well, that’s a problem because the streams and rivers that the Iberian desman inhabits are becoming polluted. Plus, there’s the additional problem of an increasing number of hydro-electric plants in that area.[04:09.18] This is leading to a fragmentation of the Iberian desman’s habitat. So, the destruction of their habitat is clearly putting them at risk.