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.
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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
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Comparatives and Superlatives
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
