Local and landscape predictors of ladybeetle natural enemy communities in urban agroecosystems
Urban agroecosystems are important ecological spaces in urban landscapes that harbor plant and insect biodiversity, and support ecosystem services like biological control. Yet the management of the urban agroecosystems, and the landscape surroundings may influence abundance and richness of natural enemies and the services they provide. Here, we assess what local factors and landscape features influence abundance and taxonomic diversity of ladybeetles, important natural enemies in gardens. In 19 urban garden sites in the Central Coast of California, we: 1) characterized local habitats (e.g., ground cover, vegetation, floral availability), 2) examined landscape surroundings (e.g., percent of urban, natural, and agricultural land nearby), and 3) sampled ladybeetles with visual surveys and sticky traps five times over the summer of 2014. To determine what garden characteristics correlate with abundance and diversity of predators in urban gardens, we first reduced the number of local and landscape variables in a principal components analysis. We then conducted a multiple linear regression analysis to identify what factors are significant predictors of ladybeetle community composition in urban gardens.
Urban agroecosystems have a high biodiversity of natural enemies, especially gardens within highly urbanized landscapes. We collected a total of 635 individual ladybeetles (visual: 246; sticky: 389) from 16 species. Ladybeetle abundance increased in the presence of buildings in gardens, and increased in gardens with higher amounts of urban area within 2 km (p=0.002, R2Adj=0.58). Similarly, ladybeetle species richness increased in the presence of buildings, with height of herbaceous vegetation, and in low intensity urban cover within 4 km (p=0.005, R2Adj=0.63). Although greater complexity of local plant communities and increased distance away from urban centers frequently increases abundance and richness of urban arthropods, we found higher abundance and richness of ladybeetles near buildings and developed land. Yet, connectivity between gardens within urban landscapes may have greater influence on local predator communities and their movement than just degree of urbanization or location. Our results call for investigation on impacts of urban matrix permeability for abundance and richness. Concluding, urban agroecosystems are significant for natural enemy communities that contribute to biological control. Even gardens in highly developed areas can support functional diversity of insects and the ecosystem services that they provide to gardener communities.