Decentralized communication, trail connectivity and emergent benefits of ant pheromone trail networks

Communication improves decision-making for group-living animals, especially during foraging, facilitating exploitation of resources. Here we model the trail-based foraging strategy of Pharaoh's ants to understand the limits and constraints of a specific group foraging strategy. To minimise assumptions we used model parameters acquired through behavioural study. Pharaoh's ants (Monomorium pharaonis) exploit the geometry of trail networks bifurcations to make U-turns, if they are walking the wrong way. However, 7% of foragers perform apparently incorrect U-turns. These seemingly maladaptive U-turns are performed by a consistent minority of specialist U-turners that make frequent U-turns on trails and lay trail pheromones much more frequently compared to the rest of the colony. Our study shows a key role for U-turning ants in maintaining the connectivity of pheromone trails. We produced an agent-based model of a heterogeneous ant community where 7% of agents were specialised frequent U-turners whilst the remaining 93% rarely U-turned. Simulations showed that heterogeneous colonies enjoyed significantly greater success at foraging for distant food resources compared to behaviourally homogeneous colonies. The presence of a cohort of specialised trail-layers maintains a well-connected network of trails which ensures that food discoveries are rapidly linked back to the nest. This decentralised information transfer might ensure that foragers can respond to dynamic changes in food distribution, thereby allowing more individuals in a group to benefit by successfully locating food finds. © 2010 Springer-Verlag.