PhD. Student University of California Santa Cruz, California
Like other urban green spaces, urban community gardens can act as biodiversity refugees, especially for small organisms like arthropods. In turn, arthropods can provide important ecosystem pest control services to these agroecosystems. Thus, an often-asked question among urban gardeners is how to improve gardens and surrounding areas for natural enemies and associated pest control services. We examine how local vegetation and garden characteristics, as well as the surrounding landscape composition affect ground-dwelling beetles (Coleoptera: Carabidae and Staphylinidae), spiders (Aranea), opilionids (Opilionida), and ladybird beetles (Coleoptera: Coccinellidae), all of which are important pest predators. In the summer 2019, we collected predators, vegetation, ground cover, and garden and landscape characteristic data of ten community gardens in the city of Seattle, Washington. We found that different groups of natural enemies are affected by different environmental variables and at different scales; probably because of differences in their dispersal capabilities, habits, and diets. Floral variables (# of flowers, # of species in flower) had a negative effect on non-flying natural enemies (spiders, opilionids, and ground-dwelling beetles), but not on flying ones (ladybird beetles). Other components of vegetation complexity benefited both flying and non-flying natural enemies. Predominantly foliage-dwelling spiders and ladybird beetles showed similarity in their responses to these variables. The only taxa that was significantly affected by a landscape-scale variable was Opilionida, the only group examined that exclusively disperses by ground. Our results show contrasting results to similar studies in different regions and highlight the need to expand the taxa and regions of study.
