Processes of eco-evolutionary metacommunity assembly in insular ecosystems with special emphasis on ancient Lake Ohrid
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One of the major challenges of eco-evolutionary research is to understand how metacommunity structuring processes scale up over time and imprint evolutionary dynamics. Insular ecosystems are suitable systems to study the eco-evolutionary intersection due to ecological, evolutionary, and geological processes occurring on similar timescales. Island Biogeography Theory (IBT) postulates that available niche space varies over the life cycle of an insular ecosystem and regulates insular biodiversity through the feedback of available niche space on immigration, speciation, and extinction rates. Competitive interaction among species for ecological resources and/or geographical space occurs on short time scale and at the level of the metacommunity. In concert with dispersal limitation and the sorting of species along environmental gradients according to their ecological niche, it should therefore also shape metacommunity structure by affecting the assembly of local communities. Metacommunity structure in turn is pivotal for diversification where different metacommunity dynamics may scale up over time to distinct biodiversity trajectories.However, there is limited empirical evidence on whether the processes shaping the co-existence of species in local communities in insular ecosystems imprint the species richness and endemism trajectories through time. In order to address this knowledge gap, this synthesis (i) summarized how individual level processes theoretically scale up to shape macroevolutionary dynamics, (ii) compiled confirmatory and contradictory evidence for such a mechanistic link from several insular ecosystems, putting specific emphasis on gastropods of the model system Lake Ohrid, and (iii) outlined future avenues for enhancing the understanding of the consequences of metacommunity processes on short timescales on evolutionary dynamics over long timescales.
Simulation experiments suggested a differential upscaling of metacommunity assembly processes over time, resulting in distinct macroevolutionary diversification dynamics. This offers the possibility to infer mechanisms of species co-existence from evolutionary dynamics and vice versa. Results of empirical studies across several taxa like cichlids, lizards, spiders, and plants of different insular ecosystems such as Lake Tanganyika and the Carribean and Hawaiian Islands, suggest a match between declining diversification rate and community assembly driven by biotic interactions. In contrast, the demonstrated diversification decline for Madagascan herpetofauna is not reflected by their metacommunity assembly processes.
For the gastropods of Lake Ohrid, a new approach of inferring metacommunity assembly processes revealed a high importance of dispersal limitation and environmental filtering, whereas competitive interaction played a minor role in structuring gastropod communities. Over long timescales, weak competitive interaction may be caused by plenty vacant niche space, which is a scenario meshing with the identified constant diversification, and that results on evolutionary timescales in a higher species richness than under strong competitive interaction. The identified assembly processes may therefore explain the evolution of the high endemic gastropod richness of Lake Ohrid. In order to improve our understanding of the reciprocal effect between metacommunity assembly processes and diversification dynamics, this synthesis presented new approaches for estimating time-varying diversification rates for 219 insular communities arising from multiple colonization events and outlines a way to infer the importance of community assembly processes needed for a mechanistical upscaling to the observed diversification dynamics over time.
The eco-evolutionary dynamic of mainly dispersal limited community assembly and constant geographic speciation resulted in the gradual build-up of Lake Ohrid’s gastropod diversity through time. This and the suggested approaches to infer diversification dynamics and the way to link them to metacommunity assembly contribute to the aim of inferring the driving forces of biotic evolution in Lake Ohrid.