Cityscape quality and resource manipulation affect natural enemy biodiversity in and fidelity to urban agroecosystems

Abstract

Context Complex landscapes with high resource availability can support more diverse natural enemy communities and better natural pest control by providing resources and facilitating organism dispersal. Moreover, in agricultural landscapes, local agroecosystem management can support biodiversity maintenance and pest control by adding resources in less complex landscapes with fewer resources. However, we lack an understanding of how local and landscape factors interact to affect natural enemy communities and their site fidelity to agroecosystems in urban landscapes (i.e., cityscapes). Objective To better understand how local and landscape factors influence natural enemies in urban agroecosystems, we used urban community gardens as a model system to test if and how local resource manipulation and differences in cityscape quality affect natural enemy (ladybird beetles, parasitoid wasps) communities and their fidelity to urban habitats. Methods We performed two manipulations. First, we added local floral resources in 6 of 12 gardens situated in different cityscapes to measure differences in natural enemy biodiversity. Second, in those 12 gardens, with and without resource additions, we manipulated populations of a common natural enemy, Hippodamia convergens, to assess fidelity to the gardens. Results Floral resource additions increased parasitoid abundance and changed community composition, but had little effect on ladybeetle abundance, richness or site fidelity. Rather, ladybeetle fidelity to gardens was lower in gardens in low quality cityscapes with high impervious cover. Conclusions Cityscape quality influences natural enemies in and fidelity to gardens. Landscape-moderated biodiversity patterns observed in rural landscapes likely differ from urban contexts with implications for pest control.

Context Matters: Contrasting Ladybird Beetle Responses to Urban Environments across Two US Regions

“…We found that urban gardens are supporting more abundant and diverse ladybird beetle populations in more urban areas in California, while in Michigan, ladybird beetles in urban gardens decline in abundance, species richness and diversity with increasing amounts of impervious cover and faster urbanization rates in most instances. Urbanization is clearly driving the abundance, species richness and behavior of ladybird beetles in California, as we have found in previous studies [29,50]. However, we show that this is not the case in another environmental context (Michigan).…”

Gardener demographics, experience, and motivations drive differences in plant species richness and composition in urban gardens

“…The gardens range in size from 444 to 15,525 m² and serve between 5 and 92 different gardeners (or gardener families). All gardens are managed with organic practices but vary in age (6-40 yrs), local habitat characteristics, i.e., vegetation cover, crop richness, and floral abundance, and landscape surroundings (Egerer et al 2018). The population is ethnically diverse, including recent immigrants (from countries including Mexico, El Salvador, Iran, Bosnia, and Vietnam) and long-time residents of California.…”

Level of urbanization and habitat type, and not patch size, influence predacious arthropod diversity patterns of urban grasslands in South Africa

“…The positive correlation between coccinellid abundance observed in our study could therefore also be linked to the higher urbanization levels in HPD, which could have influenced the abundance of aphids (originating from nearby garden floras), and subsequently, coccinellids. Furthermore, Egerer et al (2018b) reported that higher coccinellid abundance and richness was maintained in garden within low-quality cityscapes i.e. areas with more impervious surfaces, thus suggesting that higher levels of urbanization as encountered in HPD would not affect this predatory arthropod group.…”