Part I
Professor: So, continuing our discussion of ecological systems, whole systems. The main thing to keep in mind here is the interrelationships. The species in a system, 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 waterways.
Professor: Good, good, go on.
Student: Like, well, you can see how it's 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, after Europeans…
一个系统中的物种，甚至地貌本身，它们都是相互依存的。
1. interrelationship|ˌɪntərɪˈleɪʃnʃɪp|
noun. the way in which two or more things or people are connected and affect each other 相互关联；相互影响
E.g.: A branch of science concerned with the interrelationship of organisms and their environment.
关注有机体和他们与环境相互关系的一门科学。
2. interdependent |ˌɪntədɪˈpendənt|
adj. that depend on each other; consisting of parts that depend on each other （各部分）相互依存的，相互依赖的
E.g.: We live in an increasingly interdependent world.
我们生活在一个越来越相互依赖的世界。
3. settle|ˈsetl|
verb. to make your permanent home in a country or an area as colonists 殖民；作为移民在殖民地定居
E.g.: This region was settled by the Dutch in the nineteenth century.
荷兰人于十九世纪来到这一地区定居。
Part II
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, we’ll come back to where you were headed.
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.
Professor: And that creates wetlands. OK, tell me more.
Student: Well, with wetlands, it's 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.
海狸生活在溪流和河流附近，它们用原木、木棍和泥土堵住溪流和河流。
1. head |hed|
verb. to move in a particular direction 朝（某方向）行进
E.g.: Can you forecast where the economy is heading?
你能预测经济的发展方向吗？
2. back up
to become blocked so that movement or flow is slowed or stopped 阻塞
E.g.: The drain backed up [=clogged] and had to be unclogged by a plumber.
排水管堵塞，必须由水管工疏通一下。
3. pond 池塘, spring 泉, brook/stream 溪流, lake 湖, reservoir 水库, marsh/swamp 沼泽
4. standing |ˈstændɪŋ|
adj. not flowing : stagnant不流动的
E.g.: standing water
死水
5. swift |swɪft|
adj. moving very quickly; able to move very quickly 快速移动的;速度非常快的
E.g.: With a swift movement, Matthew Jerrold sat upright.
马修· 杰罗尔德迅速坐直了。
Part III
Professor: More important for our discussion, wetland areas support a lot more varieties of life than swiftly flowing water. For example, there are more varieties of fish, of 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 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 surface of the land. Think of wetlands as, Umm, like a giant sponge, the earth soaks up a lot of this water that's 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 own drinking water today. Alright…So, back to the beavers, what if the beavers weren't there?
然后还有那些不能在流水附近生长的树木和植物，却可以在死水附近开始生长。
1. mammal 哺乳动物，rodent 啮齿动物，amphibian 两栖动物，reptile 爬行动物，mollusk 软体动物，arthropod 节肢动物
2. sponge |spʌndʒ|
noun. sponge is a very light soft substance with lots of little holes in it, which can be either artificial or natural. It is used to clean things or as a soft layer 海绵；人造海绵
E.g.: He wiped off the table with a sponge.
他用一块海绵擦桌子。
3. soak up
to take in or absorb liquid 吸收，吸掉（液体）
E.g.: Use a cloth to soak up some of the excess water.
用布把多余的水吸去。
Part IV
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 let's go back to where you were 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 for 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?
Student: Well, if there is less standing water, then the ecosystem can’t support as many species, because a lot of insects and fish and frogs can't live in running water, and then the birds and animals that eat them, lose their food supply.
所以海狸被大量猎杀，过度猎杀，到1800年代它们几乎灭绝，所以…这意味着更少的湿地，更少的死水。
1. continental|ˌkɒntɪˈnentl|
adj. the continental United States consists of all the states which are situated on the continent of North America, as opposed to Hawaii and territories such as the Virgin Islands (除夏威夷、美属维尔京群岛等之外)美国大陆的，美国本土的
E.g.: Shipping is included on orders sent within the continental U.S.
美国本土订单已含运费。
2. fur |fɜ:(r)|
noun. the skin of an animal with the fur still on it, used especially for making clothes （动物的）毛皮
E.g.: The animal is hunted for its fur.
狩猎这种动物是为了获取其毛皮。
Part V
Professor: Precisely, so the beaver in this ecosystem is what we 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, that's what a keystone species does in an ecosystem. It's the crucial species that keeps the system going.
Now, beaver populations are on the rise again, but there is something to think about. Consider humans as part of these ecosystems, you've 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?
将人类视为这些生态系统的一部分，你可能也听说过水资源短缺或者用水限制，尤其是在近年来的夏季。
1. precisely |prɪˈsaɪsli|
adv. used to emphasize that you agree with a statement, especially because you think it is obvious or is similar to what you have just said （加强同意的语气）对，的确如此，一点也不错
E.g.: ‘It's not that easy, is it? ’ ‘No, precisely. ’
“事情并不那么容易吧？”“对，的确不容易。”
2. keystone|ˈki:stəʊn|
noun. the central stone at the top of an arch that keeps all the other stones in position 拱顶石
3. collapse |kəˈlæps|
verb. to fall down or fall in suddenly, often after breaking apart 倒塌，坍塌
E.g.: The roof collapsed under the weight of snow.
房顶在雪的重压下突然坍塌下来。
4. population |ˌpɒpjuˈleɪʃn|
noun. a particular group of people or animals living in a particular area （统称）某领域的生物；族群
E.g.: Britain has the largest and most flourishing fox population in Europe.
英国拥有欧洲最大也是最具繁殖能力的狐狸种群。
