Opposing effects of competition and selection on macroevolutionary dynamics

The diversity of species and traits is the outcome of multiple evolutionary processes operating over millions of years. These processes affect rates of trait evolution, speciation, and extinction. A key problem is identifying the relative importance of distinct processes in driving observed patterns in species traits and phylogenetic trees. Here, we show how two processes, competition and stabilising selection, can act opposingly but still leave identifiable traces in macroevolutionary data. Building on previous simulation studies, we model the joint influence of competition and stabilising selection on rates of trait evolution, speciation completion, and extinction. We find that opposing effects result in nuanced patterns of trait evolution and diversification dynamics that, when considered in isolation, could easily lead to misinterpretation. In particular, while the best fitting likelihood model of trait evolution is typically Brownian motion when competition and stabilising selection act simultaneously, we find stronger phylogenetic signal than expected under BM and trait distributions that are distinctly platykurtic. Taken together, we suggest that by considering multiple simple metrics measuring trait evolution and diversification dynamics it may be possible, though challenging, to identify the relative contribution of these two processes operating together in macroevolutionary data.

Methods
The attached data includes the output from all simulations described in the manuscript, and empirical datasets used for analyses.