Global increase in the endemism of birds from north to south

Abstract

Endemism is a highly valuable metric for conservation because it identifies areas with irreplaceable species, ecological functions, or evolutionary lineages1-6. Global analyses of endemism currently fail to identify the most irreplaceable areas because the commonly used endemism metrics are correlated with richness, and entire regions, especially in the southern hemisphere, are regularly excluded7-11. Global patterns of endemism are therefore still insufficiently known. Here, using metrics representing irreplaceability, we unveil global patterns of avian taxonomic, functional, and phylogenetic endemism that show striking differences between hemispheres. Across all facets of diversity, endemism decreases poleward in the northern, but increases poleward in the southern, hemisphere, resulting in a global north-south increase in endemism. The pattern is driven by increasingly smaller and discontinuous landmasses towards the south leading to increasingly smaller ranges and reduced overlap in community composition, and, unexpectedly, to peaks of diversity relative to available area in the southern hemisphere. The current misapprehension of global endemism potentially compromises urgent conservation actions, drawing attention away from key areas of irreplaceability. Highly endemic southern-hemisphere communities might be especially vulnerable to the climate crisis because discontinuous landmasses impede range shifts.