Towards a mechanistic understanding of thermal niche partitioning

We develop a theoretical framework to elucidate the mechanistic basis of thermal niche partitioning in ectotherms. Using a food web module of two consumers competing for a biotic resource, we investigate how temperature effects on species' attack and mortality rates scale up to population-level outcomes of coexistence and exclusion. We find that species' differences in competitive effects arise from asymmetries generated by the non-linear temperature response of mortality: cold-adapted species experience stronger intra-specific competition than warm-adapted species; they also exert weaker competition on, and experience stronger competition from, warm-adapted species. These asymmetries become greater as seasonal fluctuations increase, generating latitudinal variation in coexistence and priority effects. Characterizing species' thermal niches in terms of mechanistic descriptions of trait responses allows for testable predictions about population-level competitive outcomes based solely o...