The eco-evolutionary assembly of complex communities with multiple interaction types

Identifying the mechanisms that generate structure in complex ecological communities is fundamental to understand their assembly. A comprehensive picture of how ecology and evolution act together to generate these patterns is in its infancy. We developed an eco-evolutionary model of community assembly that incorporates interaction-driven population dynamics and evolutionary processes, including speciation and the inheritance of interactions, to unveil the mechanisms of generation and maintenance of biodiversity in complex species interaction networks. Importantly, our model unpicks the effects of selection of interaction types from those of inheritance by comparing evolutionary assembly with assembly by invasion under different combinations of interaction types. We found that a cost-benefit balance of accumulating interactions separates communities into two distinct types. Interactions with weak benefits for the partners involved produce communities with sparse species interaction networks dominated by competition. Strongly beneficial interactions, on the other hand, give rise to highly mutualistic, more connected communities. Mutualism, driven by both selection and inheritance, facilitates the emergence of large yet stable communities with increased complexity. By contrasting the model results with empirical patterns from microbial communities, we identify potential drivers of the assembly of these complex ecosystems and their likely patterns of interaction. Our results provide a classification system of complex ecosystems based on their composition of ecological interactions, thus generating testable hypotheses on the conditions under which different community types (mutualistic vs. competitive) might emerge.