Yellowstone
National Park
Wilderness Without Wolves
Y
ellowstone National Park is home to a unique variety
of plant and animal species. But by the 1930s, the park
had lost one of its most important predators, the gray wolf.
The wolves had been killed as part of predator control
programs. Ranchers wanted to get rid of the wolves to
protect their herds of cattle.
Food Chains
Properties of Food Chains
In the past, the gray wolves were the main predators of
elk in Yellowstone. Elk are consumers —they get energy
from eating other living things. Elk mostly eat young trees,
called saplings. Among their favorites are willows. Trees
are producers, which get their energy from the Sun. There
are many more producers than consumers in
Yellowstone. Without gray wolves, the elk population
grew quickly. They ate so much that willow saplings
nearly vanished in some places.
The presence of gray wolves in
Yellowstone is restoring balance
in this food Math
chain.
Moment
In 1995, scientists brought
thirty-one gray wolves from
Canada to Yellowstone to help
restore balance. As the wolf
population has grown, the size of
the elk population has declined to
a healthier level. With fewer elk,
more willows and other saplings
are recovering.
Elk are a main food
source for gray wolves.
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Investigation File
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Bears Bulk Up
Along with the rest of the Yellowstone ecosystem, grizzly
bears have benefited from the return of gray wolves.
Grizzlies are consumers that eat a wide range of foods,
such as berries, fish, and small elk. But occasionally they
are also a special kind of consumer called scavengers.
The grizzlies make sure nothing
goes to waste by eating leftovers
from wolf kills. This food helps
them fatten up before they
hibernate for the winter. Fatter
mother bears are better able to
feed their cubs once they are born.
AN EXAMPLE OF
A Yellowstone
Food Chain
secondary
consumer
primary
consumer
gray wolf
elk
producer
Sun
willow
Energy moves from the Sun
to producers to consumers in
the this food chain.
Do You
Know?
Wolves live in family groups, called packs,
that are led by a male and female pair. Pack
members hunt together and share other duties,
such as babysitting the cubs.
scavenger
decomposer
grizzly bear
fungus
Decomposing
Dung
Elk and other large
consumers in Yellowstone make a
lot of dung! Good thing there’s a
dung-loving fungus to help clean
up! When elk eat plants, they also
eat the fungus that is growing on
the plants. This fungus passes
through the elk’s gut and comes
out in the dung. The fungus is a
decomposer —it breaks down
organic material. By decomposing
animal waste, this fungus provides
nutrients to producers.
hat-thrower
fungus
Montana
United States
Idaho
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© Learning A–Z All rights reserved.
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All the organisms in this food chain
live in Yellowstone National Park,
shown in green.
Investigation File
Food Chains } Properties of Food Chains } Yellowstone National Park
Wyoming
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