Species- and trait-based natural enemy-herbivore networks in urban agroecosystems show similar responses to management and landscape shifts

Urban agroecosystems are model systems for examining impacts of agricultural and landscape management on species richness, interactions, and ecosystem services. Local management (ground cover, floral abundance) and landscape composition (impervious surface, agriculture) impact arthropod abundance and richness. Yet, examining functional traits of natural enemies and ecological networks may enhance understanding of biological control. We examined how local management and landscape composition impact ecological network metrics of species (taxonomy) based and trait (functional group) based networks. We sampled natural enemies and herbivores from cucurbits and brassicas in gardens, compiled trait information on hunting mode, diet breadth, and body size, classified natural enemies into functional groups, and constructed networks for each crop. We examined relationships between three network metrics and seven predictor variables. We found similar species- and trait-based network results with stronger relationships for species-based networks. For brassicas, we found lower vulnerability with increased agriculture cover for species- and trait-based networks, higher interaction richness with higher brassica density, and higher urban cover, and lower interaction richness with increased agriculture cover for species- and trait-based networks, and lower trophic complementarity with more agriculture cover, for species-based networks. For cucurbit trait-based networks, we found higher vulnerability with increased agriculture and higher trophic complementarity with increased urban cover. Local management features did not often impact networks but landscape factors were important predictors of species- and trait-based networks likely due to shifts in landscape-level resource availability and spillover effects from large-scale industrial agriculture.