Effects of urbanization on trophic dynamics of arthropod communities on a common desert host plant

Urbanization is a dominant demographic trend that radically alters ecological patterns. Most urban ecology studies, however, are strictly observational, and the mechanisms underlying these patterns have not been experimentally examined in cities. We manipulated vertebrate and invertebrate predators and water availability of a common native shrub to investigate the mechanisms controlling trophic dynamics of associated arthropod communities in an outlying desert, an urban desert remnant, and a mesic yard. The outlying desert had higher diversity and greater evenness but lower abundances than urban sites. The desert remnant resembled the mesic yard in terms of arthropod seasonality, abundances, and diversity. Surprisingly, top-down pressures on arthropods were stronger in urbanized areas and controlled already elevated herbivore abundances. Predators were especially sensitive to water availability, suggesting that stress plays an important role in this trophic system. Shifts in trophic dynamics are likely common in cities and preserved remnants may not mimic the trophic structure and function of their more pristine counterparts. If these patterns hold in other urbanized areas, they would have broad implications for conservation biology given that simply preserving natural habitats in urbanizing areas may not be enough to ensure an associated fauna that reflects the more intact and less urbanized habitat. © Springer Science+Business Media, LLC 2009.