Temperate Canopy Ants: Urbanization shifts diversity and nutritional ecology

Background/Question/Methods

Urban areas are one of the fastest growing ecosystems on Earth with more than half of the human population living in cities. Urbanization often has profound ecological impacts that alter the biodiversity and ecological function of an area. Trees provide essential habitat for insects in urban areas, yet the effects of urbanization on the ecologically important community of arboreal insects remains largely unstudied. In non-urban forests, tree canopies can house up to 70% of arthropod biomass, and arboreal insects play key roles in forest nutrient cycles and community assembly. Here, we use ants as a study system to investigate how insect diversity, activity, and nutritional ecology differ in urban street-tree canopies compared to non-urban forest canopies. Ants are ubiquitous ecological indicators, well-suited to urban ecology, and the dominant arboreal insect in intact forest canopies. We use a field study of two common tree species (white oak, Quercus alba; red maple, Acer rubrum) and a novel baiting method in seven urban and seven forest sites in the Piedmont region of North Carolina, USA to characterize the arboreal ant community and its response to an urban environment.

Results/Conclusions

This study represents the first targeted survey of arboreal ants in the region. We collected at least 23 ant species in 10 genera in urban and forest tree canopies, including the invasive needle ant (Brachyponera chinensis), which was previously thought to be a poor climber. Overall, terrestrial baits attracted ants more often than arboreal baits, but arboreal baits were still occupied 65% of the time. Urban baits were occupied by ants more often than forest baits, and preliminary findings suggest urban ant biomass was higher than forest ant biomass. Ant community composition shifted with urbanization to include more tramp and non-native species. In forest tree canopies, ants show no strong nutrient preferences, but ants in urban tree canopies show a preference for protein baits over carbohydrate baits, echoing a pattern seen in tropical canopy ants. This result may indicate that urbanization changes the nutritional demands of arboreal ants, potentially altering canopy nutrient cycling.