Ecological principles affecting community structure and secondary production by zooplankton in marine and freshwater environments1

Abstract

The production dynamics of zooplankton have been studied within two alternative conceptual frameworks. Some workers have emphasized the species composition of communities and the reproductive success of individual species, whereas others have studied the flow of nutrients and energy among ecosystem components. The reduced phylogenetic diversity of lake plankton compared with marine systems has favored the development of species‐based community ecology by limnologists. Theories that promote size structure as the salient community feature have been pioneered in marine systems and sometimes adopted for freshwater work. Empirical trends in physiological processes with organism size permit some rates to be estimated from size structure alone. With few exceptions, however, coefficients derived from log‐transformed regression equations have been applied uncritically in models, and little regard has been given to the large estimation errors involved. Metrics that are based on differences between physiological processes, rather than absolute rates of individual processes, are important ecologically. Threshold food concentration is an example: it measures the relative performance of food acquisition ability compared to acquisition and maintenance costs. These integrative properties do not vary strictly with organism size and they illustrate the fact that biological entities can develop many alternative solutions to the problems they face. Such results imply that whenever resource exploitation influences community composition, organism‐specific adaptations will prove more predictive than size structure.