Optimal foraging and neighborhood competition in Aphaenogaster ants: a field experiment with inferences on seed dispersal

Abstract Optimal foraging is a theoretical framework which assumes maximization of net-energy gain. In the field, factors such as competition may alter animal behaviors and cause deviations from the general assumptions of optimal model. In August-November 2022, a field experiment was conducted which tested optimal foraging while considering intra-specific competition in seed-seeking Aphaenogaster ants (A. famelica, A. schurri) of two subtropical forests in Kunming, Yunnan, China. Density of the ant nests were estimated using distance sampling. Six pairs of neighboring ant nests (A and B) with competitive relationships were selected, with light and heavy tuna baits (resembling ant-dispersed seeds) assigned to three distance-scenarios (near A, in the middle, near B) between each pair. Blocking treatment was employed to detect possible changes under the normal vs. reduced competition stress. Time spent on different foraging phases (food discovery, removal, transportation) was recorded to investigate ant foraging strategy in relation to food load and distance from the nests. The results showed that density of the nests was 0.27(± 0.02) nests/m2. Food-searching was accelerated in the presence of competitors, with heavier foods removed faster when positioned further from the ant nests. While optimization of the foraging process benefits ants by maximizing food-gain under the competition with rivals, intra-specific competition may ultimately drive trait-evolution in myrmecochorous plants for selecting more efficient ant seed-dispersers.