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.
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 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.
脊椎动物的灭绝风险与体型大小有关，但这种假定的关系仅在选定的分类群中进行了探索，结果各不相同。我们使用新组装的、分类广泛的数据库，分析了脊椎动物六个主要类群中灭绝风险与体型（27647 个物种）和灭绝风险与分布范围大小（21294 个物种）之间的关系。我们发现，鸟类、软骨鱼类和哺乳动物的受威胁概率与体型大小呈正相关且显著相关。两栖动物、爬行动物和硬骨鱼类的关系呈双峰型。最重要的是，所有脊椎动物都存在双峰关系，表明灭绝风险在 0.035 千克的体型断点处发生变化，这表明体型最轻和最重的脊椎动物的灭绝风险较高。我们还发现分布范围大小是受威胁概率的一个重要预测因子，几乎所有分类群都存在强烈的负相关关系。对灭绝风险驱动因素的审查表明，最重的脊椎动物最受人类直接捕杀的威胁。相比之下，体型最小的脊椎动物最受栖息地丧失和改变的威胁，尤其是受污染、农业种植和伐木的影响。我们的研究结果揭示了大型和小型分类群的脆弱性，并确定了具体大小的威胁，从而为阻止正在发生的脊椎动物灭绝浪潮提供了深入的了解。此外，它们表明，如果不进行干预，人类活动将很快导致世界上脊椎动物体型分布的双重截断，从根本上重新排列我们星球上的生命结构。
