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Wolves in Yellowstone Park A Story about Ecosystem Balance

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Wolves in Yellowstone Park

A Story about Ecosystem Balance

Yellowstone: A National Park

In 1872, Yellowstone (in the state of Wyoming) was

declared the first national park in the United States.

Geologic Wonders

Yellowstone is famous for its beautiful geologic

features: hot springs, mountains, lakes, and forests.

The Beauty of Nature

But people also came to Yellowstone park to enjoy

the beautiful plants and peaceful animals, like elk.

Predators and Prey

Wolves eat elk. Some people were upset that the

beautiful elk were being eaten by the wolves.

Get Rid of the Wolves

The U.S. government gave permission to hunters to

kill the wolves. By 1926, all the wolves were gone.

Do We Need Wolves?

The park officials thought they were helping. They didn’t

understand that wolves are important to the ecosystem.

What do you think happened?

What do YOU think happened when the wolves were

gone? Write one prediction on your answer sheet.

Cause / Effect Flow Chart

Now, as you read the next section, fill in the

cause & effect chart to show what happened to

the Yellowstone ecosystem after the wolves

were gone.

When the Wolves Were Gone

Effects on Elk

With the wolves gone, the elk population grew too quickly. Thousands of elk starved because there was not enough food to feed them all.

Too Many Elk!

There were too many elk. Park rangers finally had to

shoot and kill the elk, to keep their population down.

Too Many Coyotes!

Wolves are natural predators of coyotes. When the wolves left, the coyote population also grew.

Effect on Smaller Predators

The coyotes ate too many small animals, which other

predators in Yellowstone (like foxes and badgers) eat.

Effects on Foxes and Badgers

The foxes and badgers populations decreased,

because the coyotes were taking all of their food.

Effeccts on Pronghorn Deer

Coyotes also eat baby Pronghorn deer. The

Pronghorn population declined and almost disappeared.

Effects on Trees

Plants were also affected. Elk love to eat saplings

(young trees) like aspen, cottonwood, and willow trees.

Effects on Birds

Too many elk ate the saplings, so there were fewer

trees. This means that were fewer homes for the

birds that lived in the trees.

No Homes for Birds!

The bird population of Yellowstone decreased,

because there was no place for them to live.

Effects on Beavers

Beavers eat trees. As the trees disappeared

(eaten by the elk), so did the beavers.

The Ponds Disappear

Beavers build dams that form ponds. Fewer beavers meant no ponds, and this meant no homes for the dragonflies and ducks that lived in the ponds.

Can the Problem Be Solved?

The park rangers finally realized they had a big problem.

They decided that maybe wolves needed to come back.

The Wolves Come Back

In 1995, seven wolf packs were captured

in Canada and brought to Yellowstone.

Cause / Effect Flow Chart

Now, as you read the next sections, fill in the cause &

effect chart to show what happened to the

Yellowstone ecosystem after the wolves came back.

When the Wolves Returned

Wolf Prey

The wolf packs quickly spread out and began

hunting for their favorite foods – elk and coyote.

Wolf Population Grows

With lots of elk and coyote to eat, the

wolf population grew quickly. There are

now about 150 wolves in the park.

Effect on Coyotes

Wolves hunted and killed about half of the coyotes.

Now, the coyotes stay away from the wolves.

Effect on Pronghorn Deer

With fewer coyotes, more Pronghorn fawns are able

to survive. The Pronghorn population is growing!

Effect on Smaller Predators

With fewer coyotes, smaller predators such as

foxes, owls, and badgers, now have food to eat.

Effect on Elk

The wolves are also helping to control the elk

population. Now, there are not as many starving elk.

Effect on Trees

Because there are less elk eating the trees,

the trees are starting to grow big and tall again.

Effect on Birds

With more trees, there are more homes for

birds. The birds are coming back to Yellowstone.

Effect on Beavers

Because there are more trees, the

beaver population has grown larger.

Effect on Ponds

The beavers are building dams again, creating

ponds that dragonflies and ducks can live in.

So, are wolves bad?

People thought wolves were mean

creatures that ate peaceful animals.

Why are wolves important?

But now we know that wolves NEED to hunt their

prey, or there will be too many prey animals.

Wolves are part of the ecosystem.

Wolves are an important part of the Yellowstone ecosystem.

Wolves affect the ecosystem.

When the wolves were gone, it affected many,

many other organisms – animals and plants both.

A Healthy Ecosystem Again!

Now that the wolves are back, the

Yellowstone ecosystem is getting back into

balance. It is becoming healthy again!

ALL organisms are important.

EVERY organism in an ecosystem is important.

EVERY organism affects the ecosystem community.

Why are YOUR

ecosystem’s predators important?

You are studying an ecosystem. Choose a predator in

your ecosystem. How might YOUR ecosystem be

affected if that predator were gone? Write at least 2

possible cause/effect ideas on your answer sheet.