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Ecosystems

Author(s): Deanne Erdmann MS

Energy Flow in Ecosystems

Primary production in an ecosystem predominately occurs through the photosynthetic action of autotrophs (producers) such as plants, algae, and some bacteria. Once this energy has been captured by autotrophic organisms, it is passed on to heterotrophs (consumers) in different trophic levels.

A trophic level is made of all the organisms that share the same number of energy transfers from sunlight energy (plants are the first, herbivores the second, and carnivores the third). Transfer of energy between trophic levels is inefficient because much of the energy captured is lost to building and maintaining the bodies of organisms. Less than 10% of the energy obtained by organisms at each level is available to organisms in the next trophic level. The efficiencies of different trophic levels can be illustrated in ecological pyramids, either as available energy, biomass or numbers of organisms.