Concepts and Methods of Community Ecology Applied to Freshwater Fisheries Management

Abstract

In this paper we review selected theory, hypotheses, and methods of community ecology with reference to fisheries management. Community ecology is concerned with theoretical and empirical studies of the behavior of species assemblages over space and time. Ideas that have evolved from these types of studies concerning hierarchical organization, resource partitioning, food webs, structural integration, stability, complexity, and production and their relevance to fisheries management are discussed. One main conclusion confirmed by the ASPY Symposium is that the productivity of fish communities is determined by energy inputs, nutrients, edaphic factors, and habitat variables but that the distribution of the production by species is strongly influenced by interactions between species. A related conclusion is that species interactions are size dependent because of morphological, physiological, and behavioral constraints on predator–prey relationships, resulting in a hierarchical organization. Further, density-dependent interactions (predation, competition) within and between species influence growth rates, size distributions, and age-specific mortality and reproductive rates, and vice versa. Anthropogenic factors such as fishing, nutrient enrichment, introduction of exotic species, and chemical contaminants tend to act differentially at the level of species, but due to interdependencies between species their effects are propagated at the community level by disrupting its size- and niche-structured organization. Fish communities can be managed as relatively discrete functional units, but dependency on whole system dynamics ultimately necessitates an ecosystem perspective. Development of a more quantitative theory of fish community dynamics will require improved descriptions of species interactions (food web structure, ontogenetic histories, resource partitioning, and body size dependency), better characterization of complexity, stability, and successional change in fish communities, additional knowledge of energy transfer through aquatic ecosystems, and improved methods of estimating biomass distributions in fish communities. Comparative studies over space and time and experimental and adaptive management are appropriate ways for fishery scientists and managers to acquire this knowledge.