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Proc Natl Acad Sci U S A. 2017 Oct 3;114(40):10678-10683. doi: 10.1073/pnas.1702078114. Epub 2017 Sep 18.

Extinction risk is most acute for the world's largest and smallest vertebrates.

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Global Trophic Cascades Program, Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331;
Global Trophic Cascades Program, Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331.
School of Life and Environmental Sciences, Centre for Integrative Ecology, Deakin University, Geelong, VIC 3125, Australia.
School of Life and Environmental Sciences, University of Sydney, Sydney, NSW 2006, Australia.
School of Environmental and Forest Sciences, University of Washington, Seattle, WA 98195.
International Union for Conservation of Nature, Species Survival Commission, Gland 1196, Switzerland.
Conservation Programmes, Zoological Society of London, London NW1 4RY, United Kingdom.
Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, CA 93106.


Extinction risk in vertebrates has been linked to large body size, but this putative relationship has only been explored for select taxa, with variable results. Using a newly assembled and taxonomically expansive database, we analyzed the relationships between extinction risk and body mass (27,647 species) and between extinction risk and range size (21,294 species) for vertebrates across six main classes. We found that the probability of being threatened was positively and significantly related to body mass for birds, cartilaginous fishes, and mammals. Bimodal relationships were evident for amphibians, reptiles, and bony fishes. Most importantly, a bimodal relationship was found across all vertebrates such that extinction risk changes around a body mass breakpoint of 0.035 kg, indicating that the lightest and heaviest vertebrates have elevated extinction risk. We also found range size to be an important predictor of the probability of being threatened, with strong negative relationships across nearly all taxa. A review of the drivers of extinction risk revealed that the heaviest vertebrates are most threatened by direct killing by humans. By contrast, the lightest vertebrates are most threatened by habitat loss and modification stemming especially from pollution, agricultural cropping, and logging. Our results offer insight into halting the ongoing wave of vertebrate extinctions by revealing the vulnerability of large and small taxa, and identifying size-specific threats. Moreover, they indicate that, without intervention, anthropogenic activities will soon precipitate a double truncation of the size distribution of the world's vertebrates, fundamentally reordering the structure of life on our planet.


biodiversity; body mass; exploitation; extinction; habitat

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