阿啵呲嘚-
是an ecology class这个吧。。。
professor说:So, continuing our discussion of ecological systems:whole systems.The main thing to keep in mind here is the interrelationships. The species in the system and even the landscape itself, they r interdependent. Let"s take what u"ve read for this weekend and see if we can apply this interdependence idea. Mike?
Mike 说：well... how about beavers--ecosystems with beavers in waterways.
pro说：很好，继续。
Mike: Like, well, u can see how it"s so important, cause if u go back before European settled in north America, like before the 1600s, back when native Americans were the only people living there, well, back then there were a lot of beavers, but later on, after Europeans...
pro: OK,等等，I see where u r 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 settelers came, we"ll come back to where u were headed.
一个女生: OK, well, beavers live near streams and rivers and they block up the streams and rivers with like logs and sticks and mud. U know, they built 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.
pro: And that creates wetlands. OK, tell me more.
女生：well with wetlands, it"s like there is more standing water, more stillwater around, and that water is a lot cleaner than swiftly flowing water, because the dirt and settlement and stuff has the chance to sink to the bottom.（湿地，积水，静水，比流动的水干净）
pro: more important for our discussion, wetland areas support a lot more variety of life than swiftly flowing water. e.g. there r 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.
girl: yes, like birds and mammals that eat the fish and insects, and u can get trees and plants that begin to grow near the standing water, that can"t grow near the running water. Oh, and there"s sth. about wetland, and ground water too.
pro: OK, good. wetlands have a big affect on ground water, the amount of water below the surface of the land. Think of wetlands as, um...., like a giant sponge, the earth soaks up a lot of this water that"s continully flooding the surface, which increases the amount of water below. So there"s a wetland, u get a lot of ground water, and ground water happens to be a big source of our own drinking water today. back to the beavers, what if the beavers weren"t there?
Mike又开始说了：u just have a regular running stream, because there"s no dam, so the ecosystem would be completely different, there would be fewer wetlands.
Professor: Exactly, so, now let"s go back to where u were headed before, Mike. u mentioned the change that occured after Europeans came to North America.
Mike: Yeah, well, there used to be beavers all over the place, something like 200 million beavers, just in the continental US. But when Eurepeans 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 r almost extinct by the 1800s, so.... that meant fewer wetlands, less standing water.
pr: and what does that mean for the ecosystem? Kate?
Kate应该就是上面的女生（我只有音频了）: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 critical species that keeps the system going. now, beaver populations are on the rise again, but there"s sth. to think about- consider humans as part of these ecosystems.u"ve probably heard about water shortage or restreictions on how much water u 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?
大致就是一个prefessor让同学回去看了关于生态系统内部关系的文章。然后讨论。
然后Mike就讲到beaver了，他像从欧洲人入住之后来讲。教授希望先讲一下beaver在欧洲人来之前的居住环境。然后是一个女生讲了。说beaver居住，block的河流，然后wetland出现，就意味着地下水。professor顺便补充，wetland对于物种多样性很重要。Mike 讲，北美人来了之后为盈利捕杀河狸，导致河狸数目减少，湿地减少。Kate说时下河狸数量又在增加，但是我们考虑生态系统，还要考虑到人类的因素。
河狸的生活习性可以去查一下，多看看这些，对听力也有帮助的。
行为习性：夜间活动，白天很少出洞，善游泳和潜水，不冬眠。河狸一个独特的本领是垒坝，河狸
百度百科：凡是河狸栖息或是栖息过的地方，都有一片池塘、湖泊或沼泽。河狸总是孜孜不倦地用树枝、石块和软泥垒成堤坝，以阻挡溪流的去路，小则汇合为池塘，大则可成为面积达数公顷的湖泊。河狸具有改造自己栖息环境的能力。当进入新的栖息地或栖息地水位下降时，河狸会用树枝、泥巴等筑坝蓄水，以保护洞口位于水下，防止天敌侵扰。河狸有时为了将岸上筑坝用的建筑材料搬运至截流坝里，不惜开挖长达百米的运河。河狸在陆地上行动缓慢而笨拙，不远离水边活动。其自卫能力很弱，胆小，喜欢安静的环境，一遇惊吓和危险即跳入水中，并用尾有力拍打水面，以警告同类。
分享好知识！