LB 9-81 - Herbivore and natural enemy metacommunity structure in urban agroecosystems

Urban green spaces, such as urban gardens, are distributed as patches of habitat capable of supporting high amounts of biodiversity within a larger mosaic of urban landscape. Arthropods dispersing between urban gardens thus represent metacommunities of interacting species, including herbivore pests and their natural enemies. The metacommunity dynamics of these arthropods thus have consequences for the long term persistence of natural enemies and biological pest control in urban agriculture. This study takes a pattern-based approach to investigate the metacommunity structure of herbivores and natural enemies in 24 community garden sites in the California central coast. We use the elements of metacommunity structure framework paired with a canonical correspondence analysis to determine the ideological structure of arthropod metacommunities and assess garden habitat (e.g. garden size, vegetation cover, ground cover) and landscape characteristics (e.g. percent urban cover, landscape diversity) as drivers of metacommunity structure. We found that herbivores are best described by a nested subsets pattern while natural enemies follow a Clementsian pattern, indicating that the metacommunity structure of both trophic groups is non-random and suggesting that species distributions are determined by a common environmental gradient. Landscape diversity corresponded highly (CCA1 loading value = -0.812) with herbivore metacommunity structure compared to garden habitat characteristics. In contrast, the number of tree and shrub species in flower in gardens, a local habitat characteristic, corresponded highly with natural enemy metacommunity structure (CCA1 loading value = -0.74030). These results suggest that the composition of the urban landscape has a stronger impact on herbivore metacommunity structure, while the resources provided by urban garden habitats are a stronger determinant of natural enemy metacommunity structure. Thus, by adding resources important for natural enemies, like flowering trees and shrubs, gardeners may be able to promote metacommunities of natural enemies in this region.