Species traits mediate terrestrial mammal density responses to human impacts

Human activities are reshaping ecosystems, but their effects on species population density remain poorly understood. Most studies focus on species presence–absence, thus limiting insight into how anthropogenic pressures affect population density. Emerging evidence suggests that responses of natural populations to human disturbance are highly variable, often contingent on species‐specific traits. Here, we test how species traits mediate the density responses of terrestrial mammal populations to different forms of human impact. We quantified the correlations between mammalian population densities and urban cover, cropland cover, and human population abundance, using 7785 population density estimates across 263 species belonging to 18 taxonomic orders. Using Bayesian inference, we then conducted three phylogenetically corrected correlation meta‐analyses, and subsequently tested the effects of body mass, diet, and life history traits on the correlations using meta‐regression models. We found no overall directional effect on mammal population density with any of the three human impact variables, however, responses to impact gradients deviated from these overall effects depending on species' traits. Omnivores and large‐bodied species density was positively correlated with agricultural cover, herbivores and frugivores density declined with urbanization and human population density. We also found weaker evidence that large carnivores declined with human population abundance and urbanization, while reproductive strategy and velocity mediated responses to urbanization and cropland. Anthropogenic landscapes, where natural habitat is interspersed with anthropogenic land use and human settlements, do not support lower population density on average, but alter species relative abundance by favouring some species over others. Higher densities can result from multiple factors, including resource supplementation, ecological release effects due to the decrease or disappearance of competitor or predator species, or density compensation associated with shifts toward smaller‐bodied assemblages. This study underscores the complexity of human–nature interactions and the importance of species traits in mediating ecological outcomes.