Urbanisation Favours Ground Beetle (Carabidae) Species That Prefer Dry Soils and Have Reduced Dispersal Capacity

Urbanisation imposes strong environmental filters on ecological communities through habitat fragmentation, increased local temperatures, pollution, and the presence of invasive species. Species possessing functional traits that enable them to tolerate these conditions are expected to become more prevalent in highly urbanised areas. However, it remains unclear whether cities with similar climates and regional species pools show comparable trait-urbanisation relationships. We examined how five functional traits of carabid beetles (Coleoptera: Carabidae) vary along an urban-rural gradient in two climatically and geographically similar UK cities: Liverpool and Manchester. Eighty grassland sites were sampled along an urban-rural gradient in Liverpool and Manchester using pitfall traps. Variation in the community-weighted mean (CWM) values of traits was analysed along a gradient of percentage impervious surface cover for the two cities independently and combined. We found that CWM latitudinal range, the proportion of macropterous (long-winged) individuals, and the proportion of individuals of wet soil-preferring species declined with increasing urbanisation in the combined dataset. Trait responses were not identical across cities: the proportion of individuals of wet soil-preferring species declined with increasing urbanisation in Manchester only, whereas the proportion of macropterous individuals declined with increasing urbanisation in Liverpool only. Our findings demonstrate that even ecologically similar cities can differ in the trait-based responses of local beetle assemblages, reinforcing the need for multi-city sampling in urban ecology. We also highlight that urbanisation can favour species adapted to dry soils and those with reduced dispersal capacity, challenging commonly held assumptions about the advantages of flight in fragmented landscapes.