Human pressure homogenises species and traits globally

Human pressures, particularly urbanisation and agricultural expansion, profoundly affect biodiversity by reshaping species and functional trait distributions, with critical consequences for ecosystem resilience and multifunctionality. Yet, the extent and strength of these impacts across diverse taxa and ecosystems remain poorly understood. Here, we analyse 160 spatial datasets, encompassing over 13,000 local communities and nine major taxa in freshwater and terrestrial ecosystems worldwide. Our results reveal that human pressure is the dominant driver of species and trait replacement, consistently outweighing the effects of climate and spatial distance. Despite observing a prevalence of biotic differentiation across landscapes, we reveal that the occurrence of biotic homogenisation is consistently linked to the dominant effects of human pressure. These homogenising effects are particularly pronounced in the trait composition of terrestrial communities and the species composition of freshwater communities, suggesting distinct mechanisms across realms. We find that rates of species and trait replacement increase rapidly along the human pressure gradient, especially between low and medium pressure, before they stabilise. Importantly, an exception occurs in urban landscapes, where species replacement increases exponentially. Although ecological communities generally exhibit species turnover along the human pressure gradient, we find that they are disproportionately homogenised in traits. While this provides resilience to environmental changes, it can delay the recognition of species collapse until key functional traits are lost, risking sudden ecosystem breakdown. Our findings underscore the urgent need for conservation strategies that prioritise the preservation of minimally impacted habitats to sustain ecosystem resilience and multifunctionality.