Ant species richness in the urban mosaic: size is more important than location

Urban environments are one of the fastest growing habitats in the world. We collected ants to study community composition in three urban engineered habitats; city parks, green rooftops, and street medians in Chicago. We addressed two questions about how ant communities respond to the urban mosaic based on the observation that human disturbance increases from green rooftops to urban parks to street medians; first we studied if ant communities on green rooftops, urban parks, and street medians differed or if different types of urban greenspace have similar communities. We determined that different habitats contain distinct communities. Second, we predicted that area would impact species richness in the same way in different habitats. We found that the area of a habitat predicts species richness and community composition but the pattern was not the same in each habitat. Street medians had more ant species than urban parks, which had more species than green rooftops. On average urban parks were larger than street medians which were larger than green rooftops. Ant community composition on green rooftops differed from city parks and street medians, and showed the greatest variability within a given habitat. After accounting for area, isolation from other sites was also a significant predictor of variation in ant community structure. These findings reinforce that urban ecosystems cannot be considered as one large habitat, but would be better approached as a mosaic of interconnected habitats.