Functional homogenization of terrestrial mammals outside protected areas in the Hengduan Mountains, China

Despite the crucial role of human impacts on biodiversity loss, many assessments of this loss focus on single metrics, such as species richness, and overlook the multidimensional effects of human activities. Because of its importance to ecosystem functioning, we investigated the functional diversity of medium- and large-sized mammal assemblages in protected and unprotected mountain forests in the Hengduan Mountains of southwest China. We hypothesized that anthropogenic pressures outside protected areas (PAs) favor generalist species and lead to functionally homogenized assemblages compared with assemblages inside PAs. Using generalized dissimilarity models, we also examined the key drivers shaping patterns of functional β diversity in these landscapes. Outside PAs, functional richness was markedly lower, trait space was significantly more homogeneous, and nestedness β diversity was more prevalent (57.6%) than inside PAs, clear indications of functional homogenization. Anthropogenic variables consistently outweighed environmental gradients and spatial distance in explaining variation in functional β diversity. Our results demonstrate that anthropogenic pressure affects trait composition in ways that species counts alone do not fully capture, emphasizing the importance of conservation strategies that protect both functional integrity and taxonomic diversity.