Ecological and evolutionary assembly processes and metacommunity structure

Abstract: This thesis aims to elucidate the link between abiotic and biotic effects and biogeographical contingencies, eco-evolutionary assembly processes, and community structure in a spatially explicit metacommunity framework. To this end, we used structure analysis of naturally sampled and experimentally manipulated marine bacterial communities and mathematical eco-evolutionary modeling and simulations of metacommunity assembly. We showed that marine bacterial communities are dictated by abiotically driven assembly processes ("habitat filtering") (Paper I) and that the community composition can be highly affected by environmental stress (Papers II and III). Intriguingly, community composition in marine bacterial communities does however not seem to affect community function. In addition, we provided the first "proof" of a direct link between abiotic environmental stress and community phylogenetic clustering (Paper IV). Consequently, we tested and support the "habitat filtering" hypothesis. Further, we concluded that alternative methods need to be developed for a more thorough investigation of the effect of both ecological and evolutionary processes and biogeography. The theoretical studies showed that environmental differences among, e.g., islands, lakes or forest fragments (regional complexity) and the number of available niches within each habitat (habitat complexity) dictate ecological and evolutionary processes such as colonization into novel habitats, invasion between established communities and local evolutionary branching. When habitats are different, species will be adapted to one or few habitats only. Consequently, although dispersal may be facilitated, colonization into novel habitats will be low. When habitat complexity is high, there will initially be many niches available locally. These niches will be filled by local sympatric speciation. Consequently, high habitat complexity leads to fast local branching. Invasion into already established communities will be contingent on both regional and habitat complexity. For the same reasons as for colonization, invasion is facilitated by low regional complexity. However, niches must also be available for species to invade. Consequently, invasion is highest when habitat complexity is high and regional complexity is low. The relative rate between these processes will ultimately result in different types of speciation modes (Paper VI) and community structure (Paper V). This thesis provide a synthetic view of how communities and metacommunities are structured by ecological and evolutionary assembly processes on different spatial scales. It provides a framework for process inference from community structure analysis. Further, this thesis contains methodological approaches that can provide further knowledge about several interesting topics within the scope of metacommunity assembly and structure.