The latitudinal gradient in rates of evolution for bird beaks, a species interaction trait

Benjamin Freeman, Thomas Weeks, Dolph Schluter & Joseph Tobias Tobias
Where is evolution fastest? The biotic interactions hypothesis proposes that greater species richness creates more ecological opportunity, driving faster evolution at low latitudes, whereas the “empty niches” hypothesis proposes that ecological opportunity is greater where diversity is low, spurring faster evolution at high latitudes. We tested these contrasting predictions by analyzing rates of beak evolution for a global dataset of 1141 avian sister species. Rates of beak size evolution are similar across latitudes, with some...
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