Causal relationships between population stability and food-web topology

Abstract

1. Historically, food-web theory has examined the aspects of natural communities that areresponsible for maintaining stability in complex communities. The two main lines of researchemphasize either topological aspects damping the propagation of perturbations, or popula-tion–stability mechanisms that regulate population outbreaks and prevent a total system desta-bilization. Recent studies, however, have demonstrated that these two aspects actsynergistically to produce a single conceptual framework. 2. Nevertheless, causal relationships are still unexplored: it remains uncertain if topologicalpatterns maintain population stability, or alternatively, if population stability promotes food-web topology. 3. In this contribution, we explored the causal relationships between food-web topology andpopulation stability within complex communities. We generated food webs, using three modelswith specific biological assumptions, and measured three population-stability variables, i.e. theproportion of locally stable three-species and four-species modules and the proportion ofstable matrices; and two topo logical variables, i.e. modularity and degree of omnivory. Wethen used path analysis to evaluate two causality hypotheses, in which (i) topology promotespopulation stability, and (ii) population stability promotes food-web topology. 4. We found that populati on stability promoted food-web topology for all models, despite thedifferent biological assumptions. We also observed consistent causal relationships betweenvariables, in accordance with recent literature. 5. These results suggest that studies that intend to discuss the appearance of omnivorous beha-viour or the stabilization aspect of compartmentalization, should first consider the stability ofpopulation dynamics. Additionally, they strongly support a recently proposed theory of anintrinsic mechanism to natural communities, selecting topologies capable of producing an equi-librium point where all species could coexist, and shaping natural communities to a similarand consistent pattern.