Herbivores - not predators - may face a higher risk of extinction among mammals, birds, and reptiles, according to a new study of more than 44,000 living and extinct species. The findings suggest herbivores have consistently suffered the highest threat of extinction in the present day, the recent past, and the late Pleistocene - more so than species from any other position on the food web. Although there is strong evidence that large vertebrates are most affected by the current wave of extinctions, scientists have mainly relied on anecdotal evidence and correlations with species traits that are linked to extinction risk to understand which trophic group faces the greatest threat of extinction. Because predators have extensive home ranges and slow population growth rates - and because previous research has often focused on specific predators - many researchers have assumed that predators are most at risk of extinction. "There is so much data out there and sometimes you just need someone to organize it," says Trisha Atwood, the first author of the study. "We scoured the scientific literature and collated the diet information for over 44,600 living and extinct animal species. This allowed us to finally build a dataset so we could determine which trophic level is at highest risk for extinction." The researchers first examined modern day extinction risk patterns among herbivores, omnivores, and predators, comparing threat patterns in mammals, birds, and reptiles belonging to different trophic groups from around the world. Next, they explored how past extinctions may have shaped modern patterns by examining the proportions of recently extinct mammal, bird, and reptile species and late Pleistocene extinct mammals in each trophic group. Finally, Atwood et al. examined how body size and trophic group together affect threat status in 22,166 species. The researchers note that predators living in marine habitats did face an elevated extinction risk, suggesting that ocean predators may be facing greater existential pressures than their land-dwelling counterparts.
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