One of the most exciting scientific findings of the past half century has been the discovery of widespread trophic cascades. A trophic cascade is an ecological process which starts at the top of the food chain, and tumbles all the way down to the bottom. And the classic example is what happened in the Yellowstone National Park in the United States when wolves were reintroduced in 1995.
過去半個世紀中最令人興奮的科學發現之一就是大範圍營養瀑布效應的發現。營養瀑布是一個發生在食物鏈頂端，然後一路向下至底層的生態過程。而經典的例子是 1995 年美國黃石國家公園內狼群被重新引入時所發生的事。
Now, we all know that wolves kill various species of animals, but perhaps we're slightly less aware that they give life to many others. Before the wolves turned up, they'd been absent for 70 years, the numbers of deer, because there had been nothing to hunt them, had built up and built up in the Yellowstone Park. And despite efforts by humans to control them, they had managed to reduce much of the vegetation there to almost nothing. They had just grazed it away. But as soon as the wolves arrived, even though they were few in number, they started to have the most remarkable effects.
現在，我們都知道狼會獵殺許多不同種類的動物，但或許我們有些沒注意到牠們振興其他許多物種。在狼群到來前 (牠們已經缺席七十年了)，鹿的數量 (因為沒有任何動物去獵食牠們) 在黃石公園內增加再增加。而儘管人類做了努力去控管牠們，牠們仍已將那兒的植被減少到幾乎空無一物。牠們就是把植物吃個精光。但狼群一抵達時－－即便牠們的數量稀少－－牠們就開始產生最不尋常的影響。
First, of course, they killed some of the deer, but that wasn't the major thing. Much more significantly, they radically changed the behavior of the deer. The deer started avoiding certain parts of the park, the places where they could be trapped most easily, particularly the valleys and the gorges, and immediately those places started to regenerate. In some areas, the height of the trees quintupled in just six years. Bare valley sides quickly became forests of aspen and willow and cottonwood, and as soon as that happened, the birds started moving in: the number of songbirds and migratory birds started to increase greatly. The number of beavers started to increase because beavers like to eat the trees.
And beavers, like wolves, are ecosystem engineers, they create niches for other species. And the dams they built in the rivers provided habitats for otters, and muskrats, and ducks, and fish, and reptiles, and amphibians. The wolves killed coyotes, and as a result of that, the number of rabbits and mice began to rise, which meant more hawks, more weasels, more foxes, more badgers. Ravens and bald eagles came down to feed on the carrion that the wolves had left. Bears fed on it too, and their population began to rise as well, partly also because there were more berries growing on the regenerating shrubs. And the bears reinforced the impact of the wolves by killing some of the calves of the deer.
But here's where it gets really interesting, the wolves changed the behavior of the rivers. They began to meander less; there was less erosion; the channels narrowed; more pools formed more riffle sections, all of which were great for wildlife habitats. The rivers changed in response to the wolves. And the reason was that the regenerating forests stabilized the banks so that they collapsed less often, so the rivers became more fixed in their course.
Similarly, by driving the deer out of some places, and the vegetation recovering on the valley sides, there was less soil erosion because the vegetation stabilized that as well. So the wolves, small in number, transformed not just the ecosystem of the Yellowstone National Park, this huge area of land, but also its physical geography.
- 「出現、到來」- Turn Up
Before the wolves turned up, they'd been absent for 70 years...
- 「對...的反應」- In Response To
The rivers changed in response to the wolves.
- 「把...趕出去」- Drive Out
Similarly, by driving the deer out of some places, and the vegetation recovering on the valley sides, there was less soil erosion...