Patterns and drivers of taxonomic and functional changes in oceanic island bird assemblages

Oceanic islands are among the most transformed ecosystems in the world, with many having experienced major biotic changes through the combined effects of species extinctions and introductions. We map global patterns of taxonomic and functional change in 64 oceanic island bird assemblages and investigate whether these patterns can be explained by either island characteristics (geography, climate) or anthropogenic factors (human occupation, connectivity). The Hawaiian and Mascarene islands stand out as hotspots of taxonomic and functional change, but all islands changed taxonomically and functionally, mostly gaining species but losing functional richness. Island isolation and aridity can explain some of the observed variation in levels of change, but anthropogenic factors have a stronger effect. Remote humid islands have a stronger susceptibility to assemblage turnover and should be prioritized for conservation through the protection of native species and their ecosystems, and by preventing further introductions.