Biological traits of seabirds predict extinction risk and vulnerability to anthropogenic threats

ABSTRACT Aim Seabirds are heavily threatened by anthropogenic activities, and their conservation status is deteriorating rapidly. Nonetheless, these pressures are unlikely to impact all species uniformly. It remains an open question whether seabirds with similar ecological roles are responding similarly to human pressures. Our aims were as follows: (a) to test whether threatened versus non‐threatened seabirds are separated in trait space; (b) to quantify the similarity of species' roles (redundancy) per IUCN Red List Category; and (c) to identify traits that render species vulnerable to anthropogenic threats. Location Global. Time period Contemporary. Major taxa studied Seabirds. Methods We compile and impute eight traits that relate to species' vulnerabilities and ecosystem functioning across 341 seabird species. Using these traits, we build a mixed‐data principal component analysis of species' trait space. We quantify trait redundancy using the unique trait combinations (UTCs) approach. Finally, we undertake a similarity of percentages analysis to identify which traits explain the greatest difference between threat groups. Results We find that seabirds segregate in trait space based on IUCN threat status, indicating that anthropogenic impacts are selectively removing large, long‐lived, pelagic surface feeders with narrow habitat breadths. We also find that threatened species have higher trait redundancy, whereas non‐threatened species have relatively limited redundancy. Finally, we find that species with narrow habitat breadths, fast reproductive speeds and varied diets are more likely to be threatened by habitat‐modifying processes (e.g., pollution and natural system modifications), whereas pelagic specialists with slow reproductive speeds and varied diets are vulnerable to threats that directly impact survival and fecundity (e.g., invasive species and biological resource use) and climate change. Species with no threats are non‐pelagic specialists with invertebrate diets and fast reproductive speeds. Main conclusions Our results suggest that both threatened and non‐threatened species contribute unique ecological strategies. Consequently, conserving both threat groups, but importantly with contrasting approaches, might avoid potential changes in ecosystem functioning and stability.

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