A major goal of ecology is to understand how natural communities of species are assembled. Community assembly is a dynamical process affected by both regional (the sequence of species immigrations from the regional pool) and local (niche determinism) factors. Theoretical research has so far focused on two extreme scenarios of assembly: (i) ecological assembly, according to which communities are built solely from immigration and invasions, and (ii) evolutionary assembly, in which community assembly results from the local evolution and diversification of an ancestral species. These two opposite situations may correspond respectively to well connected communities, in which immigration is high and local evolution has little time to proceed, and to very isolated communities, such as remote islands, in which adaptive diversification has much time to occur. Still, most cases of interest are expected to lie somewhere in between these two limit cases. We need to understand better how immigration and evolution interact in the course of community assembly.  

Results/Conclusions

Here we investigated the dynamics of community assembly when both immigration and evolution (represented by the adaptive coevolution of species traits) are operating. We show that evolution cooperates with immigration, making community assembly faster and less variable. Evolution also reduces or eliminates the ``overshooting'' phase distinctive of ecological assembly trajectories. These effects are shown to result from changes in the average fate of immigrant species: by changing niche shadows, evolution makes invasive species more likely to add into a community without driving any species to extinction, and thus reduces species turnover. These results appear to be quite general, and their relevance is discussed in light of observed rates of evolution and immigration.