How Wolves Change Rivers

When wolves were reintroduced to Yellowstone National Park in the United States after being absent nearly 70 years, the most remarkable "trophic cascade" occurred. What is a trophic cascade and how exactly do wolves change rivers? George Monbiot explains.


What does it eat?

Wolf

Antelope

Fox

Bear

Beaver

Raven

Song bird

Bald eagle

Muskrat

Mice

Elk

Deer

Salmon

Coyote

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12 terms

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True or False

1. A trophic cascade is an ecological disaster.

2. Wolves were reintroduced to Yellowstone after not being there for a long time..

3. There were not enough deer in the Yellowstone Park

4. The wolves changed the behaviour of the deer.

5. The deer started to avoid the valleys because of the wolves.

6. The birds started attacking the deer

7. The height of the trees started to go down.

8. The bears started to kill each other

9. The rivers became deep and began to flow faster

10. There are now too many wolves in the park.

 

How Wolves Change Rivers

Fill in the gaps and then check:

How Wolves Change Rivers

One of the most exciting scientific f___________ of the past half century has been the discovery of widespread trophic cascades. A trophic cascade is an ecological process which starts at the t_____ of the food chain and tumbles a___ 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 r______________ in 1995.

Now, we – we all know that wolves kill various s___________ of animals, but perhaps we’re slightly less aware that they g______ life to many others.

Before the wolves t________ 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 d_________ efforts by humans to control them they’d managed to reduce much the v____________ there to almost nothing. They had just g_________ it away.

But as soon as the wolves arrived, even though they were few in number they started to have the most remarkable e_______.

First, of course, they killed some of the deer but that wasn’t the major thing. Much more significantly, they r___________ 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 g________ and immediately those places started to r_____________. In some areas, the height of the trees quintupled in j____ six years. Bare valley sides quickly became forests of aspen and willow and cottonwood. And as soon as that happened, the birds started m________ in. The number of songbirds and migratory birds started to increase g_________. The number of beavers started to increase because beavers like to eat the trees. And beavers, like wolves, are ecosystem engineers. They c_______ niches for other species. And the dams they built in the rivers provided h__________ for otters and muscrats and ducks and fish and reptiles and amphibians.

The wolves killed coyotes and as a r________ of that, the number rabbits and mice began to r_____ 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 f___ 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 r__________ the impact of the wolves by killing some of the calves of the deer.

But h_____ where it gets really interesting.

The wolves changed the behavior of the rivers. They began to meander less. There was less e_______. The channels n_________. More pools f_________. More riffle sections. All of which were g______ for wildlife habitats. The rivers changed in r_________ to the wolves. And the reason was that the regenerating forests stabilized the b______ so that they collapsed less o_____. So the rivers became more fixed in their c_______.

S___________, by driving the deer o____ of some places, and the vegetation recovering on the valley side, there was less s____ erosion because the vegetation stabilized that as well. So the wolves, s______ in number, transformed n___ just the ecosystem of the Yellowstone National Park – This huge area of land… b___ also, its physical geography.

Pronunciation focus

ly

particularly

similarly

immediately

slightly

dipthongs

stabilized

trophic

erosion

Yellowstone

v

vegetation

valley

wolves

recovering

Second syllable stress

effects

regenerating

transformed

erosion

immediately

particularly

ju:

reduced

reintroduced

huge

population