Urbanisation globally reduces functional diversity across multiple taxa

Background/Question/Methods

Cities can host significant biological diversity. Yet, urbanisation leads to the loss of habitats and, potentially, to local extinctions. Understanding how multiple taxa respond to urbanisation globally is essential to promote biodiversity conservation in cities. Using an unprecedented dataset with site-level occurrence and trait data of 5,302 species from six taxonomic groups across 379 cities on 6 continents, we investigate how urbanisation shapes the community trait-composition and diversity of six taxonomic groups (amphibians, bats, bees, birds, carabid beetles, and reptiles) across the globe.

Results/Conclusions

We show that urbanisation affects community functional diversity globally through taxon-specific changes in trait composition leading to a contraction of trait space across taxa. Urbanisation impacts all traits, with traits related to reproductive strategy and mobility consistently showing the strongest response. The effect of urbanisation on community trait composition is important across all taxa and, in birds and reptiles, exceeds that of latitude and climate. As functional diversity is linked to the resilience of ecological systems, the observed contraction of trait space threatens the capacity of urban environments to respond to challenges such as climate change, further habitat loss, and other disruptions. Maximising functional diversity within and among cities should thus become pivotal in conservation and management programmes.