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Despite being conspicuous and influential features of the biosphere, urban ecosystems have been neglected in ecological research. Arthropods are abundant in urban settings, but little is known about how these animals respond to urbanization. We systematically monitored the structure of ground arthropod communities for 12 months at 16 sites representing the four most abundant forms of urban land use (residential, industrial, agricultural, and desert remnant) in a rapidly growing metropolitan area (Phoenix, AZ). Although taxonomic richness was comparable among land-use types, community composition differed, with certain taxa being uniquely associated with each form of land use. Three taxa (springtails, ants, and mites) were extremely widespread and abundant, accounting for over 92% of captures; when these three taxa were excluded from analysis, however, differences were revealed in arthropod community composition with urban land use. Trophic dynamics also varied with land use: predators, herbivores, and detritivores were most abundant in agricultural sites, while omnivores were equally abundant in all forms of land use. These community-level differences resulted from taxon-specific responses to habitat structure, which varied with land use. Because arthropod community structure is affected by habitat structure and land use, and because arthropods play key roles in nutrient cycling, organic matter decomposition, pollination, and soil aeration, the spatial heterogeneity of urban ecosystems therefore may affect ecosystem functioning. (C) 2001 Elsevier Science B.V. All rights reserved.