Slide 1
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Energy Flow Through An
Ecosystem
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Slide 2
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Energy Flow Through an
Ecosystem
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– An ecosystem
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Slide 3
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Figure 19.20
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Slide 4
An ecosystem is characterized by
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– Energy flow
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– Chemical cycling
• The use and reuse of chemical
elements within the ecosystem.
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Slide 5
Energy flow and chemical cycling
• Depend on the transfer of substances in
the feeding relationships, or trophic
structure, of an ecosystem.
– Trophic relationships
– Trophic levels
• Divide the species of an ecosystem based on
their main sources of nutrition.
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Slide 6
Energy Flow
– Energy
• Enters an ecosystem by sunlight.
Autotrophs convert the light energy to
chemical energy
• Flows through an ecosystem when
consumers feed on producers.
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Slide 7
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Energy Flow
• As chemical energy is used by organisms
some is lost as heat energy and the
ecosystem would eventually run out of
energy
• This means that
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Slide 8
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Energy Flow Models
• Ecologists use models to describe the flow
of energy through an ecosystem:
– Food chain – the specific sequence in which
energy is transferred from one trophic level to
another
– Food web –
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Slide 9
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Figure 19.21
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Slide 10
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Food Chains
– Herbivores, which eat plants, algae, or
autotrophic bacteria, are the primary consumers
of an ecosystem.
– Above the primary consumers, the trophic levels
are made up of carnivores, which eat the
consumers from the levels below:
• Secondary consumers include many small
mammals, such as rodents, and small fishes that
eat zooplankton.
• Tertiary consumers, such as snakes, eat mice and
other. secondary consumers.
• Quaternary consumers include hawks and killer
whales.
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Slide 11
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Figure 19.22
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Slide 12
Food Chains
– Detritivores, or decomposers,
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• Are often left off of most food chain
diagrams.
• Recycle most of the ecosystem’s
organic materials to inorganic
compounds that producers can use
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Slide 13
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Figure 19.23
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Slide 14
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Food Webs
– The feeding relationships in an ecosystem
• Are typically not as simple as in an
unbranched food chain.
• The interrelated food chains of an
ecosystem are usually woven into
elaborate food webs.
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Slide 15
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Figure 19.26
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Slide 16
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Energy Pyramids
– An energy pyramid
• Compares the different trophic levels
• The trophic levels are in the shape of
a pyramid with the producer at the
base.
• The number of trophic levels is limited
by the amount of energy available in
the ecosystem.
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Slide 17
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Figure 19.25
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Slide 18
Energy Pyramids
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– Reason: At each trophic level some
energy is always used for growth and
survival, and some is lost as heat. This
energy is not available for the next
trophic level.
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Slide 19
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Figure 19.27
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Slide 20
Ecosystem Energetics and
Human Nutrition
– The dynamics of energy flow apply to
the human population.
– Eating producers instead of consumers
requires less photosynthetic productivity
and reduces the impact on the
environment.
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Slide 21
Chemical Cycling in
Ecosystems
– Biogeochemical cycles
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Slide 22
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Figure 19.28
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Slide 23
Chemical Cycling in Ecosystems
– Three key points to biogeochemical
cycles:
• Each circuit has an abiotic reservoir.
• Some chemicals require processing
before they are available as inorganic
nutrients
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Slide 24
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Figure 19.29a
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