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1、【托福听力备考】TPO13 听力文本 Lecture 2 众所周知，托福TPO材料是备考托福听力最好的材料。相信众多备考托福的同学也一直 在练习这套材料，那么在以下内容中我们就为大家带来托福TPO听力练习的文本，希望能为 大家的备考带来帮助。 TPO 13 Lecture 2 Ecology Narrator: Listen to part of a lecture in an ecology class. Professor: So, continuing our discussion of ecological systems- whole systems. The main thing
2、to keep in mind here is the interrelationships. The species in a system uh. and even the landscape itself, they are interdependent. Let s take what you read for this week and see if we can apply this interdependence idea. Mike? Student: Well, um, how about beavers- ecosystems with beavers and waterw
3、ays. Professor: Good, good, go on. Student: Like, well, you can see how its so important, cause if you go back before European settled in north America, like before the 1600s, back when native Americans were the only people living here, well, back then there were a lot of beavers, but later on, afte
4、r Europeans Professor: OK, wait, I see where you are heading with this, but before we go into how European settlement affected the ecosystem, tell me this- what kind of environment do beavers live in? Think about what it was like before the Europeans settlers came, well come back to where you were h
5、eaded. Student: OK, well, beavers live near streams and rivers and they block up the streams and rivers with like logs and sticks and mud. You know, they build dams that really slow down the flow of the stream. So then the water backs up, and creates like a pond that floods the nearby land. Professo
6、r: And that creates wetlands. OK, tell me more. Student: Well with wetlands, its like there is more standing water, more still water around, and that water is a lot cleaner than swiftly flowing water, because the dirt and sediment and stuff has a chance to sink to the bottom. Professor: More importa
7、nt for our discussion, wetland areas support a lot more varieties of life than swiftly flowing water. For example, there are more varieties of fish, or insects, lots of frog spices, and then species that rely on those species start to live near the wetlands too. Student: Yes, like birds and mammals
8、that eat the fish and insects, and you get trees and plants that begin to grow near the standing water that can t grow near the running water. Oh, and there s something about wetlands and groundwater too. Professor: OK, good. Wetlands have a big effect on groundwater, the amount of water below the s
9、urface of the land. Think of wetlands as, Umm, like a giant sponge, the earth soaks up a lot of this water thats continually flooding the surface, which increases the amount of water below. So where there re wetlands, you get a lot of groundwater, and groundwater happens to be a big source of our ow
10、n drinking water today. Alright So, back to the beavers, what if the beavers werent there? Student: You just have a regular running stream, because there is no dam, so the ecosystem would be completely different, there would be fewer wetlands. Professor: Exactly, so, now lets go back to where you we
11、re headed before, Mike. You mentioned a change that occurred after Europeans came to North America. Student: Yeah, well, there used to be beavers all over the place, something like 200 million beavers, just in the continental United States. But when Europeans came, they started hunting the beavers f
12、or their fur, because beaver fur is really warm, and it was really popular for making hats in Europe. So the beavers were hunted a lot, overhunted, they are almost extinct by the 1800s, so that meant fewer wetlands, less standing water. Professor: And what does that mean for the ecosystem? Kate? Stu
13、dent: Well if there is less standing water, then the ecosystem cant support as many species, because a lot of insects and fish and frogs cant live in running water, and then the birds and animals that eat them, lose their food supply. Professor: Precisely, so the beaver in this ecosystem is what we
14、call a keystone species. The term keystone kind of explains itself. In architecture, a keystone in an archway or doorway is the stone that holds the whole thing together, and keeps it from collapsing. Well, thats what a keystone species does in an ecosystem. It s the crucial species that keeps the s
15、ystem going. Now, beaver populations are on the rise again, but there is something to think about. Consider humans as part of these ecosystems, youve probably heard about water shortages or restrictions on how much water you can use, especially in the summer time, in recent years. And remember what I said about groundwater; imagine if we still have all those beavers around, all those wetlands. What would our water supply be like then? 希望这些对你的托福备考有帮助，预祝大家托福考试能取得理想成绩。
