Community assembly of island mammal metacommunities: The role of the regional species pool

One of community ecology’s fundamental challenges is to identify the community assembly mechanisms that shape diversity patterns. Previous studies have largely focused on the relative influence of neutral and niche-based mechanisms on community composition within a single region. However, the influence of the species pool on these mechanisms remains relatively unexplored, despite its potentially pivotal role in community assembly. The functional diversity available within the species pool is particularly relevant, as it could regulate how strongly species are sorted into local environmental niches. Here, we investigate how the species pool’s functional diversity influences the relative importance of dispersal and environmental filtering (i.e. species sorting) in structuring taxonomic, functional, and phylogenetic β-diversity patterns within 9 insular non-volant mammal metacommunities, distributed across the globe. We find that dispersal limitation largely drives phylogenetic turnover patterns, suggesting that colonization is the primary obstacle during community assembly of insular metacommunities. However, we did not find a universal trend in the relative importance of dispersal and environmental filtering across metacommunities. The functional diversity available within the species pool was also not consistently related to the strength of species sorting. We conclude that the ecological model of species sorting does not adequately represent community assembly. This raises questions about how the incorporation of evolutionary processes such as speciation and adaptation into the metacommunity framework would improve our understanding of community assembly.