The qualitative approach in investigating the role of species interactions on stability of natural communities

Abstract

Community models with competition and mutualism are qualitatively analyzed using the methodology of loop analysis combined with computer stochastic simulation. The concept of “moving equilibrium” in the growth rate of the species is discussed in 14 “tables of predictions”, presented as analytical tools that can help to shed light on controversial ecological issues such as direct versus indirect interaction and positive feedback effects on stability. While the stochastic simulation shows that only little or no difference exists in probability of stability between models with competition and models with mutualism, the related tables of predictions show that the networks among links are able to activate indirect interactions, with both negative and positive effects, between any pair of species. This phenomenon makes it difficult to determine how much stability is related to the direct interactions.