Energy Flow in Ecosystems: A Historical Review

A generalized model of energy flow applicable both to individual populations and food chains is discussed. The basic ideas of energy flow and trophic levels are described, and it is emphasized that the concept of trophic level is not primarily applicable to individual species. The efficacy of rates of population energy flow as a measure of importance in community function is stressed, and the disadvantages associated with measures of density and biomass are pointed out. Finally, the historical development of energy-oriented thinking in ecology is traced in a series of ten steps dating from the late 19th century. The growing importance of systems analysis and the use of computer models to simulate ecological functions are recognized as major areas of emphasis during the next decade.