Competition through ritualized aggressive interactions between sympatric colonies in solitary foraging neotropical ants

Abstract

Understanding the structure of food competition between conspecifics in their natural settings is paramount to addressing more complex questions in ecology, evolution, and conservation. While much research on ants focuses on aggressive food competition between large and foraging trail-using societies, we lack a thorough understanding of inter-colony competition in socially less derived, solitarily foraging species. To fill this gap, we explored the activity of ten neighbouring colonies of the giant ant Dinoponera quadriceps, monitoring 2513 foraging trips of hundreds of workers and all its inter-individual interactions. We found that, on encountering, workers from different colonies rarely engaged in aggressive fights but instead avoided each other or performed ritualised agonistic bouts. We discovered that during foraging trips, a few workers within each colony repeatedly rubbed their gaster on the substrate, a behaviour not observed in the field before. We propose that workers use this behaviour to mark the foraging area and mark more frequently in its periphery. Only 25% of the individuals specialised in this behaviour, and we hypothesise that the specialisation results from the history of interactions and experience of individual foragers. Our study suggests that workers of contiguous D. quadriceps colonies engage in low-risk conflict, mainly displaying ritualised behaviours. As these small societies mainly rely on tiny, unpredictably scattered, albeit abundant in the environment, arthropod prey, and not on persistent food sources, they do not aggressively defend exclusive foraging territories. On the other hand, colonies rely on large overlapping foraging areas to sustain their survival and growth, most often tolerating foragers from nearby colonies. We discuss whether this type of competitive interaction is expected in all solitary foraging species.