LAUSR

Significance Human activities can drive both species’ range contractions and expansions. Species’ responses to human activities are suggested to be influenced by their geographic range sizes. Here, we test the idea that human impacts cause range declines in small-range species but promote range expansion of common species, using distribution data for 9,701 plants across China to examine the relation of human activities to the degree to which species fill their climatic potential ranges. We found that narrow-ranged and widespread species indeed exhibited opposing responses to human activities, with their range filling decreasing and increasing with human influence, respectively. These findings suggest that human activities have reduced ranges of narrow-ranged species but expanded those of widespread species, causing biotic homogenization across China. Human activities have shaped large-scale distributions of many species, driving both range contractions and expansions. Species differ naturally in range size, with small-range species concentrated in particular geographic areas and potentially deviating ecologically from widespread species. Hence, species’ responses to human activities may be influenced by their geographic range sizes, but if and how this happens are poorly understood. Here, we use a comprehensive distribution database and species distribution modeling to examine if and how human activities have affected the extent to which 9,701 vascular plants fill their climatic potential ranges in China. We find that narrow-ranged species have lower range filling and widespread species have higher range filling in the human-dominated southeastern part of China, compared with their counterparts distributed in the less human-influenced northwestern part. Variations in range filling across species and space are strongly associated with indicators of human activities (human population density, human footprint, and proportion of cropland) even after controlling for alternative drivers. Importantly, narrow-ranged and widespread species show negative and positive range-filling relationships to these human indicators, respectively. Our results illustrate that floras risk biotic homogenization as a consequence of anthropogenic activities, with narrow-ranged species becoming replaced by widespread species. Because narrow-ranged species are more numerous than widespread species in nature, negative impacts of human activities will be prevalent. Our findings highlight the importance of establishing more protected areas and zones of reduced human activities to safeguard the rich flora of China.