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Narrator:Listen to a part of a lecture in an ecology class.
獨白:聽下面一段生態(tài)學上的演講。
Professor:So, continuing our discussion of ecological systems-whole systems.
教授:那么我們繼續(xù)回到生態(tài)系統(tǒng)的問題—整個系統(tǒng)上來。
The main thing to keep in mind here is the interrelationships.
這里我們要記住的一點是相互關系。
The species in the system err…and even the landscape itself, they are interdependent.
生態(tài)系統(tǒng)中的各種類生物，呃，甚至是地形地貌本身，都是相互依賴的。
Let's take what you've read for this weekend and see if we can apply this interdependence idea. Mike?
現(xiàn)在大家回顧一下這周讀的文章，看看是否可以運用這種相互依賴的理念，麥克？
Student:Well, um…, how about beavers-ecosystems with beavers in waterways.
學生:嗯，海貍的例子怎樣，水道中生長的海貍的生態(tài)系統(tǒng)。
Professor:Good, good, go on.
教授:很好，繼續(xù)。
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…
學生:像，嗯，你可以明白為什么這如此重要，因為如果你回到歐洲人在北美定居下來之前，大概十七世紀的時候，當美洲當?shù)厝耸蔷幼≡谀抢锏奈ㄒ痪用駮r，嗯，當時又很有海貍，而之后，在歐洲人…
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?
教授:好的，等等。我知道你要講什么了，但在我們探討歐洲人是怎么影響生態(tài)系統(tǒng)之前，告訴我，海貍的居住環(huán)境是怎樣的？
Think about what it was like before the Europeans settlers came, we'll come back to where you were headed.
想想在歐洲人定居之前，這里環(huán)境是怎樣的，我們再回到你剛剛說的話題上。
Student:OK, well, beavers live near streams and rivers and they block up the streams and rivers with like logs and sticks and mud.
學生:好的，嗯，海貍住的地方靠近溪流和河流，他們會用木塊，樹枝和泥土將溪流堵起來。
You know, they build dams that really slow down the flow of the stream.
你知道的，他們建起的堤壩確實能減低溪流的流速。
So then the water backs up, and creates like a pond that floods the nearby land.
所以水位便會上漲，形成一個池塘，水會流入附近的土地上。
Professor:And that creates wetlands. OK, tell me more.
教授:這就造成了濕地，好的，在跟我說點。
Student: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,
學生:有了濕地就有了更多靜水，這樣的水要比那些迅速流動的水顯得更加干凈，
because the dirt and settlement and stuff has the chance to sink to the bottom.
因為泥土和各種沉淀物會沉到水底。
Professor:More important for our discussion, wetland areas support a lot more variety of life than swiftly flowing water.
教授:我們要探討的更重要的一點是，濕地區(qū)域比起流動的水域能供養(yǎng)更多各種各樣的生命。
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.
比如，這些區(qū)域會有更多各種魚類或昆蟲，各種青蛙，這樣，依賴這些物種的其他物種就開始在濕地周邊生活。
Student:Yes, like birds and mammals that eat the fish and insects, and you can get trees and plants that begin to grow near the standing water, that can't grow near the running water.
學生:是的，像以魚類和昆蟲為生的魚類和哺乳動物，還有在靜水旁生長而不能在流動水域生長的樹木和各種植物。
Oh, and there's something about wetland, and groundwater too.
哦，還有濕地的其他相關，還有地下水。
Professor:OK, good.
教授:好的，
Wetlands have a big effect on ground water, the amount of water below the surface of the land.
濕地對地下水會產生很大影響，地表下的水量。
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.
嗯，把濕地想成是一個巨大的海面，地球將很多水分吸收上來，這些水持續(xù)不斷流到地表上，這增加了地下水的流量。
So where is there a wetland, you get a lot of ground water, and ground water happens to be a big source of our own drinking water today.
因此，有濕地的地方，就會有大量地下水，而地下水便是我們今天最大的飲水來源。
All right… So, back to the beavers, what if the beavers weren't there?
好的。那么，回到海貍的問題，如果海貍不在那里生長的話呢？
Student:You just have a regular running stream, because there is no dam,
學生:只有規(guī)律的流動溪流，因為那里沒有堤壩，
so the ecosystem would be completely different, there would be fewer wetlands.
所以生態(tài)系統(tǒng)會完全不同，濕地數(shù)量也就更少。
Professor:Exactly, so, now let's go back to where you were headed before, Mike.
教授:確實是，所以，現(xiàn)在我們回到剛剛你想說的。
You mentioned the change that occurred after Europeans came to North America.
你提到了歐洲人到底北美洲后發(fā)生的改變。
Student:Yeah, well, there used to be beavers all over the place, something like 200million beavers, just in the continental United States.
學生:是的，嗯，大概 2 億年前，僅在美國大陸，到處就有海貍。
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.
但當歐洲人到來時，他們開始捕獵海貍，制作毛皮產品，因為海貍毛皮確實很暖，而在歐洲，人們青睞于毛皮做的帽子。
So the beavers were hunted a lot, overhunted, they are almost extinct by the 1800s, so… that meant fewer wetlands, less standing water.
所以，海貍遭受大量捕殺，過度捕殺，19 世紀幾乎面臨滅絕，這意味著濕地越來越少，靜水越來越少。
Professor:And what does that mean for the ecosystem? Kate?
教授:那么這對于生態(tài)系統(tǒng)意味著什么呢？凱特？
Student:Well if there is less standing water than the ecosystem can support its many species, because a lot of insects and fish and frogs can't live in running water,
學生:嗯，如果靜水的量比其生態(tài)系統(tǒng)能支撐很多物種的量要少的話，因為很多昆蟲魚類和蛙類都不能在流動水中生存，
and then the birds and animals that eat them, lose their foods supply.
而以這些生物為食的鳥類和其他動物便會在此失去其食物供給。
Professor:Precisely, so the beaver in this ecosystem is what we call a keystone species.
教授:準確的說，那么在這種生態(tài)系統(tǒng)中的海貍就是我們所說的拱頂石物種了。
The term keystone kind of explains itself.
所謂拱頂石物種，名副其實。
In architecture, a keystone in an archway or doorway is the stone that holds the whole thing together, and keeps it from collapsing.
在建筑領域，拱道或門口的拱頂石就是支撐整棟建筑物的基石，以防其倒塌。
Well, that's what a keystone species does in an ecosystem.
嗯，這就是拱頂石物種在生態(tài)系統(tǒng)中的功能。
It's the critical species that keeps the system going.
這是保持系統(tǒng)運轉的關鍵物種。
Now, beaver populations are on the rise again, but there is something to think about.
現(xiàn)在，海貍數(shù)量再一次處于增長趨勢，但我們還要考慮某些東西。
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.
將人類當做這些生態(tài)系統(tǒng)的一部分，你可能聽過水資源稀缺或對你所能使用的水資源進行限制，特別是近些年夏天的時候。
And remember what I said about groundwater; imagine if we still have all those beavers around, all those wetlands.
記住我說過的關于地下水的問題。想象一下如果現(xiàn)在這些海貍還生活在這些濕地上。
What would our water supply be like then?
那么水資源供給會是怎樣的一種情況呢？
