Ants in an arid urban landscape: Biodiversity, community composition and factors behind the success of an exotic ant species

Urbanization, the creation of cities and their growth, is a process with profound implications for the diversity and community composition of local ecosystems. Urban environments are made up of a diverse patchwork of natural, seminatural and modified habitats that might harbor different plant and animal communities. Frequently, they include invasive or exotic organisms. In arid environments in particular, irrigated spaces constitute a novel habitat that contrasts heavily with natural environments. In the present study, I considered the biodiversity and composition of the ant communities in contrasting environments within the urban area of Tucson, Arizona. First, I assessed the relationship between plant productivity, measured using satellite imagery, ant abundance and ant diversity in irrigated parks, urban desert remnants and natural desert habitat. I found no significant differences in ant diversity among these habitats, despite clear differences in abundance and productivity. Next I considered the differences in ant species composition among the assemblages in the same three habitats. I found that each habitat included a distinct ant community, although those from desert remnants and natural desert were functionally similar to each other. Irrigated parks showed a potential to act as refuges for ant species threatened by the effects of climate change, but they also included a greater abundance of ants considered pests. Finally, I considered some of the characteristics behind the success of the only widespread exotic ant species found in urban habitats in Tucson: the dark rover ant ( Brachymyrmex patagonicus ).These ants were found in large numbers in every park sampled. As a recently introduced species, little was known of their biology. Colonies of these ants displayed aggression among each other which makes it impossible for them to form large interconnected networks of nests. Although colonies occupied nearby nests in the laboratory, under field conditions, each colony inhabited a small territory.