Eco-evolutionary assembly processes within oceanic island systems

Résumé fourni par la source

Abstract Oceanic islands provide classic model systems for the study of biotic assembly and for the role of evolutionary radiations within this process. Herein, we analyse how patterns and processes operating at local, community scales nest within the insular and archipelagic scales as biotic systems assemble over ecological and evolutionary timescales in such systems. We highlight that those insular systems large enough to accommodate evolutionary radiations exceed the scale of ecological community dynamics sensu stricto and instead constitute metacommunities, subdivided into arrays of local communities by typically complex island topography. Metacommunity assembly involves a set of filters on membership (dispersal, environmental, biotic), followed by the action of an array of in situ evolutionary processes that are amplified by local community assembly processes across these landscapes. We briefly consider the relevance of concepts of biotic equilibrium before moving on to argue for the importance of extended periods of ecological opportunity (undersaturation) to the initiation of speciation within these systems. Insular radiations tend to involve a mix of adaptive and non-adaptive evolutionary processes, and a mix of (i) geographical isolation leading to the occurrence of multiple ephemeral species with little ecological divergence followed by niche divergence in secondary sympatry; and (ii) divergent selection linked to exploitation of new environments. We develop both scenarios longitudinally, paying attention to the likely constraints on local and insular metacommunity diversity, calling upon case study evidence. Finally, we consider how island ontogeny influences the processes we have reviewed, shaping and constraining evolutionary radiations, and ultimately the balance between processes of assembly and of attrition. In conclusion we argue for increased efforts to integrate the modelling of insular geo-environmental dynamics with a multi-scalar approach to their biological dynamics.

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