Emergent Coexistence in Ecological Communities

Understanding if the co-occurrence of species in a community can be explained and predicted from pairwise interactions is a long-standing question in ecology. Recent observations have revealed that stable microbial communities contain a high number of species that cannot coexist in pairs, providing new empirical elements to explore this question from a fresh perspective. In this talk, I will show that emergent coexistence arises naturally in models of random pairwise interactions, to an extent that is consistent with empirical observations. Interestingly, this phenomenon does not require additional mechanisms like intransitive or higher-order interactions; rather, coexistence can arise from the dense networks of indirect effects. As diversity increases, indirect effects can become so intricate that pairwise interactions no longer predict community composition, revealing a fundamental decoupling between pairwise interactions and species co-occurrence. Echoing the conceptual lessons of deterministic chaos, our findings provide the theoretical foundations to understand how simple species interactions can lead to emergent coexistence patterns in ecological communities.