Ecosystems

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Ecosystems

• Chapter 54, Campbell, fifth edition
• pp. 1131-1138
• www.ent.orst.edu/schowalt/BI213/ecosys.htm

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Questions of interest How do energy and matter
move through ecosystems? How does the community
affect energy and matter flow? How do humans
influence energy and matter flow at ecosystem and
global scales?
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Trophic structure Feeding relationships
determine energy and matter flow Trophic levels
are based on source of nutrition primary
producers, consumers, detritivores
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Primary producers Also called autotrophs
Plants and bacteria that fix their own
energy photosynthesis or chemical oxidation
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Consumers Also called heterotrophs Organisms
that derive energy from autotrophs Primary
consumers feed on primary producers
Secondary (etc.) consumers feed on other
consumers Detritivores consume dead
organic matter
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Food chains vs. Food webs A food chain is the
linear pathway of energy flow from one trophic
level to another A food web represents the
multiple pathways of energy flow among organisms
at different trophic levels
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Energy Flow Fate of energy available to
ecosystem Balanced budget Available solar energy
3-10 x 106 J/m2/yr
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Primary productivity rate of light energy
conversion to chemical energy (photosynthesis)
1 of solar energy Gross primary
productivity (GPP) total primary
productivity Net primary productivity (NPP)
primary productivity stored as organic matter
(biomass), accounting for respiration
(usually 50-90 GPP) Standing crop biomass is
amount present at a particular time
Ecosystems differ in their productivity
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Secondary productivity is the rate of primary
productivity converted to consumer biomass All
energy is eventually lost as heat through
respiration Energy is not cycled
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Ecological efficiency The ratio of net
productivity at one trophic level to net
productivity at the next lower level is typically
about 10 Conformers are more efficient than
are regulators Predators are more
efficient than are herbivores Efficiency can be
represented as pyramids
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