To understand the mechanisms shaping global species diversity patterns, we focused on species assembly of bird communities on islands, which are ideal for detecting ecological and historical processes. We tested the hypotheses that species traits and island environments interactively shape the phylogenetic structure of island bird assemblages through a variety of ecological processes: habitat filtering, in-situ speciation, extinction, dispersal limitation and competitive exclusion. We assessed the effects of species ecological traits and environment factors on the phylogenetic fields, which defined as phylogenetic distance between individual bird species and co-occurred species within each island, using phylogenetic generalized linear mixed models. Climate and isolation were the most important factors driving the co-occurrence patterns of island bird species: the species' phylogenetic fields were significantly clustered on tropical and/or isolated islands. We also found that the phylogenetic fields strongly correlated with the ecological traits especially for the diet and habitat preferences: the phylogenetic fields tended to over-disperse for granivores and species inhabiting in wetlands or coasts, while frugivores showed clustered phylogenetic fields. Moreover, mobility and body size had substantial effects on species assemblages: long-distance dispersers had clustered phylogenetic fields and small-bodied species showed overdispersed phylogenetic fields.
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