英語聽力文摘455 奇妙的海洋食物鏈

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過度捕鯨與環(huán)境

Until recently, when scientists studied changes in open-ocean ecosystems, they looked at changes in the bottom of the food chain that gradually make their way to the top, like food shortages and shifts in the ocean environment. A recent study, however, suggests that more attention needs to be given to top-down influences as well.

For example, over the past few decades, there’s been a major collapse of the populations of harbor seals, fur seals, sea lions, and sea otters living on the coasts of western Alaska. Now a new study suggests that all this destruction can be traced back to humans overfishing sperm and baleen whales between 1946 and 1979.

Killer whales, who live at the top of the ocean food chain, used to prey on sperm and baleen whales. When these were no longer available, the killer whales were forced to fish farther down the food chain. First they fed on seals, which were the easiest to catch and the most nutritionally valuable.

Then, when seals became rare, the killer whales turned to sea lions. When the sea lion population crashed, they started fishing sea otters. The domino effect reaches even farther. Without sea otters keeping sea urchins in check, their population has exploded. And they’ve destroyed the kelp forests, and with it, the kelp forest ecosystem in southwestern Alaska.

Animals switching food sources can have a very serious effect on the environment. And that we humans, as the ultimate predators, need to give a lot of thought to the choices we make. They may affect the food web in unintended ways.

直到最近，當科學家們在研究遠洋地區(qū)生態(tài)系統(tǒng)的變化時，他們觀察了處于食物鏈最底層并且在慢慢上升的(生物)變化，比如說食物短缺、海洋環(huán)境的變化。然而，最近的一項調(diào)查顯示，人們還應該更多的注意(食物鏈)自上而下的影響。

比方說，在過去的幾十年里，生活在阿拉斯加西海岸的斑海豹、海狗、海獅和海獺數(shù)量極具下降。現(xiàn)在，一項新的調(diào)查顯示，所有的這些毀壞都可以歸咎于人類在1946年到1979年期間過度捕撈抹香鯨和須鯨。

虎鯨是在海洋食物鏈的最高層，它習慣于捕食抹香鯨和須鯨。當虎鯨不能再捕食它們的時候，它就被迫捕食處于更下一層的食物鏈(的生物)。她們先捕食的是最容易捕捉且最有營養(yǎng)價值的海豹。

接著，當海豹變得稀少后，虎鯨便轉(zhuǎn)向了海獅。而又當海獅的數(shù)量變少后，虎鯨又開始獵殺海獺了。多米諾效應又繼續(xù)延伸。沒了海獺約束海膽，海膽的數(shù)量變得龐大起來。并且破壞阿拉斯加啊西南部的海藻林生態(tài)系統(tǒng)。

動物間交換食物來源對環(huán)境有著很嚴重的影響。而作為終極捕食者，人類需要好好思考一下他們所做的選擇。(因為)這些選擇可能會以人們所不知道的方式來影響食物網(wǎng)。

Vocabularies and expressions：

harbor seal：斑海豹

fur seal：海狗

sea lions：海獅

sea otters：海獺

sea urchin：海膽

sperm whales：抹香鯨

baleen whales：須鯨

killer whale：虎鯨

domino effect：多米諾效應(在一個相互聯(lián)系的系統(tǒng)中，一個很小的初始能量就可能產(chǎn)生一連串的連鎖反應，也稱之為“多米諾骨牌效應”。)

kelp forest：海藻林

keep in check: 阻止，約束