Carabid beetle traits tell tales of urban filtering: shifts in activity, flight behaviour, reproduction, and overwintering

Abstract Urban environments are characterised by habitat fragmentation, sensory and chemical pollution, and altered climatic conditions. Species may either adapt to these stressors or already exhibit pre-adaptive traits. Traits mediate how species respond to cities and influence their persistence. Cities often host unique species assemblages compared to rural sites, and traits could be instrumental in understanding these community compositional changes. An array of carabid beetle species are commonly found in urban and rural environments and their ecology and traits are well known. Here, we study the trait composition and functional diversity in carabid beetle communities in response to urbanisation. We sampled carabid beetles with pitfall traps across four replicated urbanised landscapes in the Netherlands, in city centres and peaty rural pastures. We found a consistent shift in species composition between rural and urban environments, more species in rural areas but no difference in abundance. In contrast to rural communities, urban communities were characterised by later-reproducing, less frequently flying, more nocturnal and eurytopic species that more frequently overwinter as larvae. Also, we found lower functional richness and higher functional divergence in urban communities, but no difference in functional evenness and functional dispersion compared to rural sites. Our results contribute novel trait-urbanisation associations compared to earlier studies, which may be due to different geographic regions and studied urbanised landscapes and their associated differences in environment and habitat. Overall, these results hint that environmental filtering shapes urban communities. Future studies could investigate how habitat-specific characteristics influence trait composition.