Foraging time and neighborhood competition in Aphaenogaster ants: a field experiment

Intraspecific competition can significantly alter the foraging behavior of social insects. How competition might impact closely located colonies with overlapping foraging ranges is largely unknown. Between August–November 2022 and September–November 2023, we investigated the intraspecific competition of three Aphaenogaster species (A. famelica, A. schurri, and A. japonica) in two urban forests in Kunming, China. We estimated the density of ant nest openings and measured foraging distances. Nest opening density was 0.18/m (0.33/m for A. famelica, 0.03/m for A. schurri, and 0.07/m for A. japonica), and mean foraging range was 160 cm (124 cm for A. famelica, 296 cm for A. schurri, and 228 cm for A. japonica). We then ran a series of field experiments to assess the effects of distance, food load, and intraspecific competition on ant foraging. For 36 pairs of nest openings, we placed one light and one heavy tuna bait at various distances between neighboring nest openings. We modified competition intensity by physically blocking one of the nest openings and analyzed time spent on food discovery, removal, and retrieval by ant workers. Ants spent a longer time discovering baits located farther away from, and retrieving heavier or farther baits. Blocking was correlated with a longer time for food removal (for A. schurri/japonica and A. famelica) and transportation (for A. famelica). Selectivity of the light vs heavy bait was not found, suggesting neighborhood distance was too short to generate distance-based selectivity patterns. Differences in nest spacing might be related to species-specific traveling and intraspecific competition.