A comparison of whole-community and ecosystem approaches (biomass size distributions, food web analysis, network analysis, simulation models) to study the structure, function and regulation of pelagic food webs

Abstract

A step-by-step procedure for investigating the structure, function and regulation of pelagic communities as an entirety is suggested which proceeds along gradients of increasing requirements for data and knowledge, and of growing understanding of ecosystem functioning. It comprises methodologies based on biomass size distributions, followed by food web analysis, network analysis and dynamic simulation models. The different approaches are compared with respect to data requirements, theoretical foundations, operational problems, time and computational effort, and the different types of information they provide on food web structure and dynamics. These ideas are illustrated with data from Lake Constance. Biomass size distributions provide a structural and energetic food web analysis based only on measurements of abundances and body sizes, and a few general assumptions mainly on size relationships of metabolic activities and trophodynamics. Food web analysis considers binary webs depicting qualitatively trophic links between species or trophic guilds and provides profound information about the food web structure. Mass-balanced flow diagrams (trophic webs) take into account the magnitude of flows between living and non-living compartments, and provide comprehensive descriptions of fluxes and cycling of matter and the trophic food web structure when evaluated by network analysis. These three static approaches are contrasted with tactical dynamic simulation models depicting interaction webs and representing unique possibilities of studying the dynamic nature, spatio-temporal organization, direct and indirect cause-effect relationships, and impact of physical forcing. However, these capabilities are only achievable on the expenditure of a very large research effort.