Nat Res 319

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Nat Res 319
ENERGY FLOW IN ECOSYSTEMS
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Ecosystem ecology concentrates on movement of
energy and materials (e.g. nutrients) through the
community.

• currency of energy or nutrients

• comparisons of very different systems

• hard to delineate boundaries because of
• importing and exporting

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We need to measure

• biomass

• energy flow

• flow of limiting chemicals

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A food chain shows transfer of energy from source
(plant) to herbivore (primary consumer) to
primary carnivore (secondary consumer) to
secondary carnivore (tertiary consumer)...

• each step is a trophic level

• there are losses of energy between
• every level

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If we collect a number of food chains from one
community we can construct a food web
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We can depict transfers with pyramids
Biomass Silver Springs
Numbers Bluegrass Field
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Photosynthesis transforms carbon from oxidized
state (work is done using energy from sunlight).
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Energy Loss

• losses include 6 to ozone layer (ultraviolet)

• half of remaining light is infrared

• an additional 35 of visible light reflected

As a result only about 1-4 of the suns energy
reaches the earths surface
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Plants can only use certain wavelengths of light
- primarily reds and blues
Thus terrestrial plants have an
average efficiency of 2-3 and about 1 in
aquatic systems
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Definitions

• Gross Primary Production (GPP) -
• total amount of CO2 that is fixed by the plant
• in photosynthesis

• Respiration (R) - the amount of CO2
• that is lost from an organism or system from
• metabolic activity

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Definitions continued

• Net Primary Production (NPP) -
• net amount of primary production after
• the costs of respiration by plants, heterotrophs,
• and decomposers.

• Standing Crop - measure of the biomass
• of the system at a single point in time.

• Turnover - ratio of the standing crop
• to production (SC/P)
• (g/m2 divided by grams/m2/yr)

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What determines productivity?
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How do ecosystems compare?
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