Local Habitat Complexity and Its Effects on Herbivores and Predators in Urban Agroecosystems

Simple Summary Garden plants provide habitat for pests as well as the predatory insects that eat them. In rural agriculture, structurally complex vegetation that includes diverse plant species can help attract predators and enhance pest control, while dense plantings of a single plant species are often associated with pest outbreaks. However, the vegetation composition that best supports predators and pest control in urban agriculture is not yet fully understood. In this study, we measured vegetation cover, diversity, and connectivity (distance between plants) in community garden plots to better understand how vegetation complexity influences the abundance and diversity of pest and predator species and pest control. Gardens with more vegetation cover had the most abundant and diverse predators, while gardens with more diverse vegetation had fewer predators. Further, gardens with abundant predators had higher pest control, whereas gardens with more predator species had lower pest control, possibly due to antagonistic interactions between competing predator species. Our results suggest that gardens with high vegetation cover can help support more predators, which can promote higher pest control. However, pest control benefits may be limited in gardens with diverse and antagonistic predator communities.Abstract In urban community gardens, cultivated vegetation provides variable levels of habitat complexity, which can suppress pests by promoting predator diversity and improving pest control. In this study, we examine three components of the structural complexity of garden vegetation (cover, diversity, and connectivity) to investigate whether higher garden vegetation complexity leads to fewer herbivores, more predators, and higher predation. We worked in eight community gardens where we quantified vegetation complexity, sampled the arthropod community, and measured predation on corn earworm eggs. We found that plots with high vegetation cover supported higher species richness and greater abundance of predatory insects. High vegetation cover also supported a greater abundance and species richness of spiders. In contrast, high vegetation diversity was negatively associated with predator abundance. While high predator abundance was positively associated with egg predation, greater predator species richness had a negative impact on egg predation, suggesting that antagonism between predators may limit biological control. Community gardeners may thus manipulate vegetation cover and diversity to promote higher predator abundance and diversity in their plots. However, the species composition of predators and the prevalence of interspecific antagonism may ultimately determine subsequent impacts on biological pest control.