Cause-Effect Relationships in Energy Flow, Trophic Structure, and Interspecific Interactions

Abstract

Measurements of the efficiency of energy transfer between trophic levels are consistent with the hypothesis that it is trophic structure that controls the fraction of energy consumed at each trophic level, rather than energetics controlling trophic structure. Moreover, trophic structure is determined by competitive and predator-prey interactions. In freshwater pelagic communities, the collective efficiency of herbivorous plankton in consuming primary producers is up to 10 times as great as is the efficiency of forest herbivores in consuming their food. Conversely, forest predators are about three times as efficient in consuming herbivore production as are zooplanktivorous fish. The presence of an additional level, piscivorous fish, in pelagic communities accounts for the difference. In the aquatic system, herbivorous zooplankton are freed from predation by the effect of piscivorous fish on their predators; in the terrestrial system, green plants are freed from herbivory by predation on the herbivores. We ...