No complexity-stability relationship in natural communities

Understanding the mechanisms responsible for the stability and persistence of natural communities is one of the greatest challenges in ecology [1]. Robert May showed that con-trary to intuition, complex randomly built communities are less likely to be stable than simpler ones [2, 3]. For four decades, ecologists have tried to isolate the non-random charac-teristics of natural communities that could explain how they persist despite their complexity [1]. Surprisingly, few attempts have been tried to test May’s fundamental prediction and we still ignore if there is indeed a relationship between stability and complexity. Here, we performed a comparative stability analysis of 119 quantitative food webs sampled world-wide, from marine, freshwater and terrestrial habitats. Food webs were compiled using a standard methodology to build Ecopath mass-balance models. Our analysis reveals that classic descriptors of complexity (species richness, connectance and variance of interaction strengths) do not affect stability in natural food webs. Food web structure, which is far from random in real communities, reflects another form of complexity that we found influences dramatically the stability of real communities. We conclude that the occurrence of comple