Costs and Benefits of Clearing Physical Trails in Leafcutter Ants (#344)
Leafcutter ants of the genus Atta construct persistent physical trails to harvesting sites by removing undergrowth, leaf litter and debris and even flattening the soil itself. Unlike classical pheromone-based trails, construction and maintenance of these cleared trails incurs a cost to the colony both in time and in energy spent by individuals, and may divert individuals from the foraging effort. At the same time, cleared trails offer the benefit of increased movement speed for workers travelling to the harvesting site and transporting harvested leaf fragments to the nest, leading to an increase in colony productivity. Is this clearing effort worth it?
While the percentage of cleared trails in a colony’s network is high, there is of yet no understanding of what circumstances trigger trail clearing for a given trail. Can we understand the colony trail clearing behaviour in economic cost-benefit terms?
Estimates of the impact of trail clearing and maintenance costs on overall colony foraging efficiency vary. I present a model incorporating field estimates from my own work and the literature of the cost and benefits of relevant behaviours that allow calculation of the net benefits of cleared trails. I use the model to investigate the circumstances under which a net benefit of clearing trails is reached. Our results indicate that trail clearing greatly increases the overall harvesting rate. Thus, trail clearing appears to be an adaptive behaviour in Atta ants, posing the question why portions of the trail network remain uncleared, as frequently observed in the field.