Warm Temperature is Associated With Reduced Body Mass and Diversification Rates While Increasing Extinction Risks in Cold-Adapted Seabirds

Anthropogenic rapid warming has caused decreases in richness and body mass of birds following the metabolic theory of ecology; yet, the pervasiveness of these shifts remains controversial among different taxa. Here, by combining phylogenetic methods and fossil data, we synthesized spatial patterns of richness and body mass for 328 seabird species belonging to two groups: Procellariimorphae (PM) and non-Procellariimorphae (NPM). We found that the relationship between body mass and richness, as well as diversification rate, exhibits distinct patterns in these two groups. Ancestral state reconstruction analyses indicate that smaller PM, as opposed to NPM seabirds, evolved in warmer waters from larger ancestors and exhibited a slower diversification rate. Different ancestral climatic origins explain the reduced influence of environmental factors on richness patterns among PM compared to NPM seabirds. Furthermore, whereas NPM seabirds in high latitudes face a high extinction risk, warmer sea temperatures positively correlate with a high extinction risk among PM seabirds. Our results indicate that PM seabirds, evolving from cold waters, have reduced body mass and diversification rate, making them more vulnerable to warmer temperature.