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Balance in Ecosystems
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" As wolves become reestablished in Yellowstone National Park,
they kill the old, injured, and diseased elk. This process is
reducing the number of elk. The smaller elk population
is
letting more plants grow. So, the numbers of animals that eat
the plants, such as snowshoe hares, and the animals that eat
the hares, such as faxes, are increasing.
All organisms in a food web are important for the health
and balance of all other organisms in the food web. But the
debate over the introduction of wolves to Yellowstone National
Park will most likely continue for years to come.
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Energy Pyramids
Draw an energy pyramid
for a river ecosystem that
contains four levels-aquatic
plants, insect larvae, bluegill
fish, and a largemouth bass.
The plants obtain 10,000
units of energy from sunlight.
If each level uses 90% of the
energy it receives from the
previous level, how many
units of energy are available
to the bass?
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1. Use each of the following terms
in a separate sentence: herbivores,
carnivores, and omnivores.
8. Identifying
Relationships
Draw two food chains, and
depict how they link together to
form a food web.
2. In your own words, write a defi~'
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Producers use the
energy in sunlight to
make their own food.
Consumers eat producers and other organisms to gain energy.
is Food chains
represent how energy flows
from one organism to
another.
I) All organisms are important to maintain the
balance of energy in the
food web.
(I Energy pyramids show
how energy is lost at
each food chain level.
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nition for each of the following
terms: food chain, food web, and
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engers are all examples of
3. Herbivores, carnivores, and scav-
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c. consumers.
b. decomposers. d. omnivores.
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bottom of an energy pyramid?
Explain your answer.
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Consequences
What would happen if a species
disappeared from an ecosystem?
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through a food web.
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7. The plants in each square meter
of an ecosystem obtained 20,810
Calories of energy from sunlight
per year. The herbivores in that
ecosystem ate all the plants but
obtained only 3,370 Calories of
energy. How much energy did
the plants use?
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For a variety of links related to this
chapter, go to www.scilinks.org
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Topic: Food Chains and Food Webs
SciLinks code: HSM0594
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