Perceived urban microhabitat heterogeneity impacts carabid beetle communities

Context The habitat heterogeneity hypothesis predicts that increased environmental heterogeneity promotes biodiversity by providing more niches. However, few studies have examined whether human perceptions of heterogeneity align with the ecological responses of arthropods. Objectives We investigated how perceived habitat heterogeneity translates into environmental variables. Then, we explored the effects of perceived habitat heterogeneity in remnant urban forests and parks on carabid beetle species richness, composition, and functional traits. Methods We examined carabid beetle (Coleoptera, Carabidae) communities across three habitat types differing in perceived microhabitat heterogeneity: heterogeneous urban forests, homogeneous urban forests, and urban parks in Lahti, Finland. Results Environmental data confirmed distinct habitat characteristics: for most variables measured, heterogeneous forest sites were more variable compared to homogeneous forest sites. Contrary to expectations, species richness was higher in homogeneous forests and parks and lower in heterogeneous forests. Community composition differed among habitats and was influenced by canopy openness and dead wood. Heterogeneous forests harboured fewer macropterous and open-habitat species, while homogeneous forests had more brachypterous and generalist species, indicating differences in dispersal capacity and habitat preferences. Body size at the community and population levels, and mass at the population level were generally unaffected. Conclusions These results suggest that while habitat heterogeneity shapes community structure and traits, species richness does not always increase with heterogeneity, highlighting complex relationships between environmental variables and beetle communities. We underscore the importance of considering specific habitat features, such as dead wood and canopy cover, for urban biodiversity conservation.