How diversity and invasibility co-evolve along temperature gradients: predictions from eco-evolutionary dynamical models

Background/Question/Methods

Understanding the emergence and maintenance of large-scale biodiversity gradients is a long-standing challenge in ecology and evolutionary biology. Further progress requires theory unifying how key organismal, ecological, and evolutionary processes covary across space and time so as to create diversity gradients. Here we unify disparate ecological and evolutionary hypotheses for the origin of diversity gradients across temperature gradients. Using a few fundamental organismal and ecological ‘rules’, we present a general theoretical framework to predict the dynamics of community invasibility and species richness across ecological and evolutionary time scales. We show how the evolution of body size, a key organismal trait, influences the short-term ecological structure and long-term evolutionary dynamics of entire trophic networks. Further, organismal metabolism critically ties how variation in temperature then drives the rate at which the feedback between ecological and evolutionary processes proceed. Our framework distinguishes between ecological invasibility, which is governed by local ecological interactions; and evolutionary invasibility, which is governed by local ecology and constraints imposed by small phenotypic effects of mutation. 

Results/Conclusions

Our model predicts how species richness, evolutionary invasibility and ecological invasibility should vary and co-vary with temperature. Our results demonstrate the coupling of richness and invasibility by eco-evolutionary feedbacks and show that this coupling can be positive or negative depending on the type of invasibility considered and the stage of diversification. Examining covariation between richness-temperature gradients, evolutionary invasibility-temperature gradients, and ecological invasibility-temperature gradients generate new predictions that can help distinguish alternative hypotheses for the emergence of large-scale richness gradients. The model predicts that in the early to mid-stages of evolutionary history, communities tend to diversify according to a ‘diversity begets diversity’ principle. This results in a positive relationship between richness and evolutionary invasibility, whereby both increase with temperature. In the long-term, richness may not vary with temperature even though a positive relationship between evolutionary invasbility and temperature emerges and persists. This implies low invasibility and a stable species composition in warmer regions, and higher invasibility and greater species turnover in cooler regions. These results emphasize the importance of dynamical models merging organismal, ecological and evolutionary processes for advancing our understanding of large-scale biodiversity patterns.