Structural dependencies in trophic interaction strengths explain stability in natural food webs

Xiaoxiao Li , Eric Forgoston, Ursula Gaedke, Andrew P Beckerman , Peter C. de Ruiter

Ongoing biodiversity loss has intensified the need to understand what keeps complex ecological communities stable. Theory predicts that complexity destabilises communities when the strength of interactions is randomly distributed. In natural food webs, however, shared biological traits such as biomass, energy conversion efficiency and specific predation rate link various interaction strengths to one another, creating structural dependencies among them. We retained or broke these dependencies to identify how they affect stability in a three-species intraguild predation module, assess their relevance to Lake Constance food webs and test how their effects vary with complexity in bioenergetic models. Across all three systems, retaining all dependencies produced the greatest reduction in the destabilising effects of interspecific interactions. In the three-species module, retaining structural dependencies brought opposing trophic feedbacks closer in strength, contributing to greater relative stability. It also gave the closest match to empirical stability estimates for Lake Constance, even without enforcing energy balance. Such stabilising effect from interspecific interactions increased with species richness and connectance. Our findings show how non-random patterns in interaction strengths that emerge from species traits can explain stability in real food webs.