Sources of Filters for Assemblage Composition and Functional Traits Related to Movement in Urban Carabids

Insect communities are sensitive to changes in their environment, including those made by development in human dominated landscapes. Previous research has shown that as urbanization increases, the assemblage of ground beetles (Carabidae) in an area shifts towards species with higher dispersal ability. There is also a turnover of species from forest specialists to generalist and grassland specialist species. While these impacts of urbanization are well known, what characteristic of urbanization produces a given change is not well established. I captured ground beetles in unmowed spaces managed as tallgrass preserves, mowed lawns near the preserves, and mowed lawns distant from preserves. Sites were characterized by being mowed or unmowed, the percentage of impervious surface as ground cover surrounding a site, and distance to the nearest tallgrass habitat. Each ground beetle was identified to species or morphospecies and traits related to dispersal ability were recorded. To describe an insect’s dispersal ability, each beetle’s wing condition (macropterous or brachypterous) was noted, and their leg length and body size were measured. Here I compare the effects of two anthropogenic causes of site isolation and one form of disturbance on the community composition and dispersal traits of urban ground beetles. I find that each cause of isolation has an impact on different aspects of the local community. Distance to the nearest tallgrass preserve is associated with species presence/absence at a site while the amount of impervious surface surrounding the site along with mowing filter for specific dispersal traits. I also find that mowing and the impervious surface surrounding a site have opposing effects on the local community’s leg length relative to body size. These findings further our knowledge about how cities filter insect species by identifying specific components of urbanization that need to be treated separately when analyzing how urban ground beetle communities form.