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Although prairie dogs may function as keystone species in natural systems, little is known about their impacts in urban settings. We measured vegetative cover, vegetative height and density, and slope on isolated black-tailed prairie dog (Cynomys ludovicianus) colonies in semi-arid habitat along a gradient of urbanization in Denver, CO. We compared these measurements with data taken within the same colonized fragments but in areas unused by prairie dogs, and with data taken on habitat fragments entirely unoccupied by prairie dogs. As predicted, prairie dog colonies had reduced grass and litter layers, but increased forb and bare soil coverage. Plants were shorter and less dense on colonies, and slope was gentler. Grass cover was higher on uncolonized portions of fragments occupied by prairie dogs than on sites unoccupied by prairie dogs, suggesting that prairie dogs were more likely to be present on sites with high grass cover. In general, prairie dog-vegetation interactions we recorded were similar in urban fragmented landscapes to those observed in natural landscapes, providing evidence that some aspects of their ecological role are retained in urban systems. (c) 2007 Elsevier Ltd. All rights reserved.