Metacommunities in community gardens: relative strength of environmental, spatial, and social filters for species assembly in highly managed urban patches

The metacommunity approach is ideal for understanding how communities are filtered across fragmented habitats. In human-managed systems, such as cities, traditional metacommunity concepts of environmental and spatial filtering need to be adapted to include links to social factors. In this paper, we examine the relative effects of environmental filters (defined here as the biophysical characteristics of a patch that have been influenced by human management decisions at the local and landscape scale), spatial filters (defined here as distance between habitat patches, but which can also be influenced by human management decisions at the landscape scale), and social filters (defined as neighborhood socio-economic and socio-demographic factors) on the community composition of cultivated (crops and ornamentals) and non-cultivated plants (“weeds”), pollinators, and natural enemies (arthropod predators and parasitoids) in urban gardens. We surveyed the species composition of these groups in 23 community gardens in the California Central Coast. We then correlated community dissimilarity or beta-diversity between gardens with environmental, spatial, and social dissimilarity. We found that, with the exception of cultivated plants, all groups fit a metacommunity model indicative of dispersal limitation. In addition, environmental filters, including garden management factors, had a strong influence on community composition of cultivated and non-cultivated plants as well as on pollinators but not on natural enemies. Since communities that are strongly limited by dispersal are prone to local extinction events, we recommend follow-up studies to examine how to improve dispersal between green habitats in urban spaces.