Functional homogenization of terrestrial mammals outside protected areas

The ongoing biodiversity loss in the Anthropocene has led to the erosion of functional diversity, a critical component of ecosystem functioning and services. Despite the critical role of human impacts on biodiversity loss, many analyses still focus solely on single metrics like species richness, neglecting the multidimensional effects of human activities. Here, we investigated functional diversity of medium- and large-sized mammal assemblages in protected and non-protected mountain forests, hypothesizing that, anthropogenic pressures outside protected areas (PAs) would favor generalist species, leading to functionally homogenized assemblages compared to those within PAs. Using generalized dissimilarity models (GDMs), we also examined the key drivers shaping patterns of functional β-diversity in these landscapes. Functional diversity revealed stark declines outside PAs, resulting in lower functional richness than expected for a given species richness. Our results also revealed a predominance of functional clustering and a nested pattern of β-diversity in assemblages outside PAs, indicating significant functional homogenization. Additionally, anthropogenic variables were identified as the key predictors driving functional β-diversity, consistently outweighing the effects of environmental drivers and spatial distance. By addressing the functional impacts of anthropogenic pressures, our work offers insights for the development of targeted, effective conservation practices in the face of a global biodiversity crisis.