A simple dynamic model explains the diversity of island birds worldwide

Colonization, speciation and extinction are dynamic processes that influence global patterns of species richness. Island biogeography theory predicts that the contribution of these processes to the accumulation of species diversity depends on the area and isolation of the island. Notably, there has been no robust global test of this prediction for islands where speciation cannot be ignored, because neither the appropriate data nor the analytical tools have been available.

The accurate estimation of fundamental island biogeographical relationships requires suitable data from many archipelagos, but divergence-dated phylogenies of complete communities on islands remain scarce. Hence, Valente et al., produced new dated molecular phylogenies for the terrestrial avifaunas of 41 archipelagos worldwide. They refer to both true archipelagos (composed of multiple islands) and isolated insular units that consist of single islands (for example, Saint Helena) as ‘archipelago’. For each archipelago, they compiled avian taxon lists (excluding introduced, marine, migratory and aquatic species, as well as birds of prey, rails and nocturnal birds) and collected physical data. They used archipelagos as their insular unit, because the high dispersal abilities of birds within archipelagos suggest that, for birds, archipelagos can be considered equivalent to single islands for less dispersive taxa, and because archipelagos constitute the most-appropriate spatiotemporal unit for framing analyses of biodiversity patterns at a large scale

They extracted colonization and speciation times for each archipelago from the phylogenetic trees, producing a ‘global dataset’ for the 41 archipelagos, which includes the complete extant avifauna of each archipelago, plus all species known to have become extinct due to anthropogenic causes.

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