Size-dependent mortality and competition interactively shape community diversity

Body size is recognized as a major factor in evolutionary processes mediating sympatric diversification and community structuring. Life-history types with distinct body sizes can result from two fundamental mechanisms, size-dependent competition and size-dependent mortality. While previous theoretical studies investigated these two processes in separation, the model analyzed here allows both selective forces to affect body-size evolution interactively. Here we show for the first time that in the presence of size-dependent competition, size-dependent mortality can give rise to multiple, coexisting size morphs representing the final outcomes of evolution. Moreover, our results demonstrate that interactions between size-dependent competition and mortality can create characteristic abrupt changes in size structure and non-monotonic patterns of biological diversity along continuous and monotonic environmental gradients. We find that the two selective forces differentially affect the body-siz...