Colony provisioning affects use of leaf-piles in Atta cephalotes

Leaf-cutter ants harvest leaves from the trees surrounding their nest and transport them back to feed their symbiotic fungus, which is the food supply for the colony. The leaf foraging process involves many workers performing specialized tasks in a supply chain that spans from trees hundreds of meters away to the deep chambers of their subterranean nests. Piles of leaves, thought to function as caches, will occasionally form along foraging trails, especially at transition points such as gradient changes and junctions. Although previous work has shown that these leaf-piles form through positive feedback, the impacts of traffic flow on their use and their potential adaptive significance remains unclear. One proposed function of a leaf-pile is that of a stockpile - a temporary reserve that can be drawn upon to buffer fluctuations in leaf supply and demand over time. In this study, we used captive colonies of the leaf-cutter ant Atta cephalotes to analyze the relationship between ant traffic flow and leaf-pile removal. Then we increased the leaf supply of the colony to determine whether this surplus would initiate the formation of a leaf-pile, and if the increased leaves available affected the traffic-pile removal relationship. Results from this study have increased our understanding of the formation and significance of leaf-piles in leaf-cutter ant colonies, and provided insight into the functioning of self-organizing supply chains.