Climatic niche breadth determines the vulnerability of terrestrial vertebrates to future climate change

Biodiversity is essential for ecosystem stability, yet it is declining at an accelerating rate worldwide. Terrestrial vertebrates, as representative taxa, are facing severe threats, which willbe further exacerbated by future climate change. Understanding the climate change vulnerability of terrestrial vertebrates and identifying the key factors driving their vulnerability is essential for their conservation. However, most existing studies are geographically based, obscuring the direct climatic driver. Grounded in the climaticspace concept, this study first maps the climatic niches of terrestrial vertebrates (taking mammals and amphibians as examples), then predicts their vulnerability to future climate change and dissects the key drivers behind it. Both mammals and reptiles tend to have more species concentrated in the central cells of the climatic space, which is characterized by moderate climatic conditions, while fewer species occupy the marginal niches that correspond to more extreme climatic conditions. For reptiles, some marginal niches remain unoccupied. Under future climate change scenarios, the vulnerability (the proportion of habitat area loss due to falling outside the suitable climatic niche) of mammal and reptile species will increase with more aggressive development patterns, and reptiles are more threatened than mammals. Climatic niche breadth is a key determinant of the future vulnerability of mammals and amphibians.Species with narrower climatic niches are especially vulnerable to climate change, particularly tropical species. This study demonstrates that using climate space is a direct and sensitive approach for examining the relationship between climate and species vulnerability, and could guide both theoretical research and conservation practices in biodiversity.