Size‐Dependent Processes Underlying Regularities in Ecosystem Structure

The structure of animal communities and the energy flux through them may be characterized by biomass ratios, ecological efficiencies, and production efficiencies of the component organisms. Here, we interpret these ratios in terms of the elementary processes of food intake, specific production rate, and gross growth efficiency that underlie them. Recent information confirms that the magnitude of all these processes is related to the average body mass of the organisms involved. However, our analysis shows that this well—known dependence reflects the influence of two different basic biological properties. One of these is the metabolism—body—size relation of individual that is familiar from physiology. The other less well—recognized property appears as an ecological population factor reflected in the distribution of particle sizes within animal groups in the community and is probably related to the relative sizes and distributions of predators and their prey. It appears that both the physiological and ecological size relationships have to be recognized as scaling factors in order to transform measures of biological production of various parts of communities into common terms for comparison. Current data on the generality and stability of community structure and production suggest that by using this twofold size scaling, trophic energy flow within the community can be determined from the distribution of body sizes without the necessity of specifying trophic levels of the organisms involved. The ecological size scaling can be seen as an index of the system nature of ecosystems.