A discrete, allometric approach to the modeling of ecosystem dynamics

This work focuses on a special type of generic ecosystem model that allows for the investigation of the dynamics of ecological networks. The emphasis lies on patterns that arise from within the system and their dependency on environmental factors, and the relationship between network structure. organization and performance. The model which has been built to simulate these patterns is a highly abstracted representation of nutrient flows in a food web. It is based on allometric relationships for the physiological rates and the diversity of time scales present in the system. The functional response of predator to prey abundance is defined as a two dimensional extension of a Holling type III function. A comparison of the most commonly used predation functions reveals that neither prey- nor ratio-dependent functions can account for the different responses for very high/very low predator and prey densities. Only by employing predator and prey dependence can unrealistic behavior, as displayed by one-dimensional functions, be avoided. Finally, we show an example of the model's capability to make statements about general rules connecting ecosystem structure, organization and performance. It is found that a system's nutrient efficiency is correlated both to its functional diversity and to its temporal organization of nutrient hows. In a large number of differently structured food webs and under varying environmental conditions, the diversity of temporal and functional niches enhances the efficiency of nutrient utilization. (C) 2000 Elsevier Science B.V. All rights reserved.