Influences of priority effects, nutrients and urbanization on creosote bush arthropod communities.

摘要

This study investigated the influences of priority effects, nutrients and urbanization on the structure of creosote bush arthropod communities in Phoenix, Arizona. Surveys and field experiments were conducted at multiple sites located within two habitat types varying in degree of fragmentation; namely, fringe deserts (expanses of desert outside of Phoenix) and urban deserts (patches of desert within the urban core of Phoenix).; Arthropod communities were more rich and abundant in fringe deserts than in urban deserts. However, the proportion of herbivores, omnivores and predators did not vary between desert types. Nonetheless, in fringe deserts, communities were composed of proportionally more leaf-chewing herbivores, stalking predators and web-building predators, whereas urban deserts contained more sap-sucking herbivores and ambush predators.; Creosote bushes in urban deserts were higher in foliar carbon:phosphorus (C:P) and nitrogen:phosphorus but did not differ in carbon:nitrogen from bushes in fringe deserts. Elemental composition of creosote bush was generally unrelated to arthropod communities. However, foliar C:P was positively linked to richness of arthropod communities in urban deserts. Additionally, higher C:P bushes had greater abundances of Centrodontus atlas paucivenosus, an insect herbivore. Both relationships suggest that phosphorus may be more limiting to consumers in terrestrial habitats than previously recognized.; Finally, the influence of priority effects—where the presence of one species alters colonization by others—on the assembly of creosote bush arthropod communities was investigated experimentally. Objectives were to test (1) whether predatory pioneer colonists varying in movement rates differentially influenced community assembly, and (2) how long priority effects were detectable. Experiments consisted of defaunating bushes and then seeding them with the following pioneer colonists: (1) jumping spiders (mobile predators), (2) crab spiders (sedentary predators) or (3) no pioneers. There were no clear patterns of priority effects in urban deserts. Conversely, in fringe deserts, the presence of jumping spiders influenced community composition more than crab spiders. However, priority effects were transitory and lasted only 2 weeks. Overall, priority effects are not universally important in the assembly of creosote bush arthropod communities, and even when they do occur, the effects are ephemeral.