Urbanization is expected to reduce biodiversity; however, recent increases in the number of studies focused on urban ecology suggest a challenge to this assumption. Specifically, this body of research suggests that the influence of urban development on biodiversity is more complex than previously expected. Despite progress in understanding the impacts of urbanization on biodiversity, many gaps in our knowledge remain. Two of the most important aspects involve the consistency of biodiversity changes both among cities and over time within cities. Previous work in this area has relied on inconsistent metrics and methods to compare biodiversity changes among cities, and very few have explored the temporal turnover of communities within cities. Here, we performed fine-scale sampling of ant (Hymenoptera, Formicidae) assemblages among three cities in the Midwestern United States to quantify the consistency of biodiversity changes in urbanized landscapes. We sampled ant communities at five different levels of urbanization, from a gradient of rural to suburban to urban, and across five different time points throughout the growing season within each city.
Our results revealed idiosyncratic patterns of ant biodiversity among the three focal urbanization gradients. Most notably, our results show that urban environments do not consistently reduce biodiversity. In one of our three focal cities, we observed increases in diversity; another city showed no change in biodiversity along the rural-to-urban gradient, and another showed the expected decrease in biodiversity. Importantly, our results also show that, within cities, diversity and species assemblages were consistent across different time points throughout the growing season; this result suggests that single time point observations of urban biodiversity may be sufficient. Together, our results indicate that while the urbanization impacts on communities are fairly stable and consistent over time, they are less so over space, highlighting the uniqueness of individual cities and the complex system of factors that drive community structure.