Biodiversity in urban gardens: Factors driving predator and pollinator communities

Background/Question/Methods

Urbanization is detrimental for biodiversity due to alteration and loss of habitat, pollution, temperature changes, and invasion by exotic species. Nonetheless, green spaces within cities may offer habitat for species which otherwise could not survive in urban areas. Arthropods are the most biodiverse animals, and provide critical ecosystem services, such as pest control and pollination, with potentially important implications for urban agriculture. We studied arthropod communities in urban green spaces in Toledo, OH to document abundance and richness of common arthropod taxa and to determine those factors that drive richness and abundance of important predators and pollinators. In one study, we compared arthropod communities in three urban habitats (forests, vacant lots, and community gardens). We sampled ground-foraging arthropods with pitfall traps, and sampled vegetation, and additional site characteristics. All arthropods were identified to order and feeding group. In a second study, we tested whether presence of plants native to the Oak Openings region of NW Ohio influenced bee communities in backyard vegetable gardens. We sampled bees with elevated pan traps, netting, and observation, and sampled vegetation and floral resources. We correlated the abundance of common arthropod taxa, including predators and pollinators with vegetation and site characteristics with conditional inference trees.

Results/Conclusions

The most abundant arthropods in pitfalls were isopods, ants, harvestmen, millipedes, spiders, and beetles. Predator abundance differed by habitat; there were more millipedes and harvestmen in forests, more ants in lots, and more spiders in gardens and lots. Ant richness was higher in lots and forests, and spider richness was greater in lots and gardens. Predator abundance was strongly correlated with building cover, but predator taxa responded to building and concrete cover, shrub, tree, and herb density, vegetation height, and plant richness. Bee abundance (and native bee abundance) was higher in the gardens with native plants, and bee species composition significantly differed in gardens with and without native plants. Bee richness did not differ between gardens with and without native plants. Bee richness correlated with vegetable garden size, flower garden size, herbaceous plant cover, plant richness, and grass cover. Bee abundance correlated with native plant garden size, number of herbaceous plants, number of white flowers, and size of flower area. In sum, predator abundance and richness varies in urban habitats, and not surprisingly, different taxa respond to different site characteristics. Pollinators respond to several factors in urban gardens, but presence of native plants could be used to promote bee abundance.