Disentangling landscape and local drivers of ground-dwelling beetle community assembly in an urban ecosystem

Community assembly is the process by which local communities are organized and maintained from the regional species pool. Understanding processes of insect assembly are of interest in shrinking cities where vacant land has become abundant as a result of protracted economic decline and population loss. Vacant land represents a viable conservation space for insects such as beetles that contribute to ecosystem services including pest suppression, decomposition, and nutrient cycling. However, the inherent heterogeneity of cities may pose challenges for beetle dispersal from source populations, while quality of the urban environment may constrain establishment. The objective of this study was to investigate the constraints to ground-dwelling beetle community assembly in vacant lots and pocket prairies of Cleveland, Ohio using a functional trait-based approach. Functional traits with a strong predictive capacity for ecological functions were measured on beetle species collected via pitfall traps. Assembly of beetle communities was primarily constrained by dispersal limitations to colonization. Over 93% of species found within treatments were capable of flight, and functional diversity of beetle communities was higher across all treatments than expected by chance. Once beetles colonized, successful establishment was influenced by heavy metal contamination and mowing frequency, with these disturbances shaping communities based on body size, antennae length, and origin. Colonization of dispersal-limited species could be facilitated by increasing connectivity among greenspaces in cities, while establishment could be enhanced by managing local environmental conditions. Understanding how insect communities are structured in urban ecosystems provides context for observed patterns of biodiversity, advances conservation efforts, and fosters ecosystem services.