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3–2 Energy Flow
Ecological Pyramids
Ecological Pyramids
The amount of energy or matter in an
ecosystem can be represented by an ecological
pyramid.
An ecological pyramid is a diagram that shows
the relative amounts of energy or matter
contained within each trophic level in a food
chain or food web.
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3–2 Energy Flow
Ecological Pyramids
Ecologists recognize three different types of
ecological pyramids:
• energy pyramids
• biomass pyramids
• pyramids of numbers
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3–2 Energy Flow
Ecological Pyramids
0.1% Third-level
consumers
Energy Pyramid:
Shows the relative
amount of energy
available at each
trophic level.
1% Second-level
consumers
10% First-level
consumers
Only part of the
energy that is stored
in one trophic level is
passed on to the next
level.
100% Producers
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3–2 Energy Flow
Ecological Pyramids
The more levels that exist between a
producer and a top-level consumer in an
ecosystem, the less energy that remains from
the original amount.
Only about 10 percent of the energy
available within one trophic level is
transferred to organisms at the next
trophic level.
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Ecological Pyramids
Biomass Pyramid
The total amount of living tissue within a given
trophic level is called biomass.
Biomass is usually expressed in terms of grams of
organic matter per unit area.
A biomass pyramid represents the amount of
potential food available for each trophic level in an
ecosystem.
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3–2 Energy Flow
Ecological Pyramids
Biomass Pyramid:
Represents the amount of
living organic matter at each
trophic level. Typically, the
greatest biomass is at the base
of the pyramid.
50 grams of
human tissue
500 grams of
chicken
5000 grams
of grass
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Ecological Pyramids
Pyramid of Numbers
A pyramid of numbers shows the relative number
of individual organisms at each trophic level.
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3–2 Energy Flow
Ecological Pyramids
Pyramid of
Numbers:
Shows the relative
number of individual
organisms at each
trophic level.
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3–2 Energy Flow
Ecological Pyramids
For some ecosystems, the shape of the pyramid of
numbers is the same as that of the energy and
biomass pyramids.
However, in ecosystems where there are fewer
producers than there are consumers, such as a
forest ecosystem, the pyramid of numbers would not
resemble a typical pyramid at all.
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The main source of energy for life on Earth is
a. organic chemical compounds.
b. inorganic chemical compounds.
c. sunlight.
d. producers.
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Organisms that feed on plant and animal
remains and other dead matter are
a. detritivores.
b. carnivores.
c. herbivores.
d. autotrophs.
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How does a food web differ from a food chain?
a. A food web contains a single series of
energy transfers.
b. A food web links many food chains together.
c. A food web has only one trophic level.
d. A food web shows how energy passes from
producer to consumer.
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In a biomass pyramid, the base of the pyramid
represents the mass of
a. heterotrophs.
b. primary consumers.
c. producers.
d. top level carnivores.
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The amount of energy represented in each
trophic level of consumers in an energy pyramid
is about
a. 10% of the level below it.
b. 90% of the level below it.
c. 10% more than the level below it.
d. 90% more than the level below it.
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