Background/Question/Methods
With urbanization increasingly affecting landscapes worldwide, interest in urban biodiversity and its ecological benefits is also growing. Beetles, and particularly carabid beetles (Coleoptera: Carabidae), are common focal organisms of ecologists studying potential indicator taxa along the urban-rural gradient. However, the beetle assemblages of non-forested urban greenspace areas and those of shrinking cities with increasing ruderal vegetation are not well studied.
This study was conducted in remnant forest, community garden and vacant lot habitats in the shrinking city of Detroit from May-August of 2007. The twelve study sites (four replicates of each habitat type) were characterized using land cover and floristic measures. Pitfall traps established at the sites were opened for three days each month. Captured beetles were sorted to family, then morphospecies, and the carabid beetles were identified to species. The analysis considered the abundance, richness, and various morphological traits of the beetle assemblages in the three habitats, and considers the implications of utilizing different levels of taxonomic specificity to characterize the beetle assemblages at the study sites.
Results/Conclusions
A total of 1039 beetles, consisting of 183 morphospecies in 27 families were identified. The abundance and diversity of beetles was greatest in the gardens, where more herbaceous and predatory beetles were captured than in vacant lots or forests. Gardens and vacant lots shared several species of beetles, while forest species were chiefly exclusive to forest habitats. Vacant lots were significantly lower in beetle abundance and diversity than either of the two habitats. A comparison of beetle morphospecies, families and a subset of ground-dwelling beetles (Staphylinidae and Carabidae) found that the taxonomic grouping does affect interpretation of site similarities; the ground-dwelling beetle grouping appears to best represent the species diversity fostered by these habitats.
Of the 199 individuals of 30 carabid species captured, over half were found in forest habitats. The forest carabid beetles were predominantly large and carnivorous, and associated with open ground and canopy cover habitat characteristics. The grassy ground cover of vacant lots was found to be associated with a reduced capture rate of carabid beetles. All the habitats were dominated by flying species of carabids, indicating that the ability to migrate may be critical to surviving the isolation caused by urbanization.