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 trait-based networks. For brassicas, we found lower interaction diversity, lower vulnerability, higher functional complementarity with increases in vegetation complexity (e.g., grass cover and vegetation height).For cucurbits, vegetation height was associated with lower interaction diversity and higher functional complementarity, cucurbit density and agriculture cover boosted interaction diversity, and urban cover was associated with lower vulnerability. Thus, we found that both local and landscape features impacted networks, and that network responses varied with crop species with important potential implications for pest control.