Some Approaches to Modeling Multispecies Systems

Abstract

A qualitative taxonomy of models is presented. Fisheries models with a single-species outlook are traditional and uninvolved with the complexities of an interactive, multispecies system. Ecosystem models, because of the required aggregation of many species into units of convenience, lose track of, or become insensitive to, biological relationships. They tend to be descriptive, usually are incapable of forecasting change subsequent to specific disruption, and often run afoul of their own internal intricacies. Intermediate to these extremes are multispecies models, most of which, though idiosyncratic, are focused on the dynamics of specific ecological phenomena. These suggest that aggregation into guilds is unwarranted; that there is no correlation between primary production and community complexity; that, dependent on the coupling involved, removal of one species may work to the benefit or detriment of presumed competitors; and that community complexity (= food web design and even species composition) is imposed by higher trophic level species. Three examples illustrating that small-scale or model relationships can be recognized in open, large natural communities are given. How, but not whether, fisheries managers should respond to the difficulties presented by multispecies interactions remains unanswered.