No complexity-stability relationship in natural ecosystems

Understanding the mechanisms responsible for the stability and persistence of natural ecosystems is one of the greatest challenges in ecology. Robert May showed that contrary to intuition, complex randomly built communities are less likely to be stable than simpler ones. For four decades, ecologists have tried to isolate the non-random characteristics of natural communities that could explain how they persist despite their complexity. Surprisingly, few attempts have been tried to test May’s fundamental prediction and we still ignore if stability is indeed related to complexity. Here, we performed a comparative stability analysis of 163 quantitative food webs sampled worldwide, from marine, freshwater and terrestrial habitats. Food webs were compiled using a standard methodology to build Ecopath mass-balance models. Our analysis reveals there is no relationship between diversity and stability in natural food webs. Food web structure, which is far from random in real ecosystems, reflects another form of ecosystem complexity. Thus, we investigated the stabilizing properties of specific food web structures using randomization tests. We found that interaction type and the frequency distribution of interaction strength dramatically influence stability of real ecosystems. We conclude that the occurrence of complex ecosystems in nature is possible owing to their structural properties. The diversity-stability debate has contributed to the development of productive researches that have pointed out the key role of these properties. It is now essential to understand the mechanisms driving the emergence of food web structure to predict the impact of global change on ecosystem stabilit