Costs of trail construction and maintenance in the leaf-cutting ant Atta columbica

Abstract

Leaf-cutting ants of the genus Atta use trunk trails during foraging which may persist for months or years. The time and energy costs of trail construction and maintenance were estimated for colonies of Atta columbica on Barro Colorado Island, Panama, to determine if these costs are likely to constrain new trail construction and promote persistence of existing trails. Large workers 2.2-2.9 mm in headwidth participated in trail-clearing significantly more frequently than typical leaf-carriers, indicating that they may form a distinctive task group within the foraging force. Small litter items were carried off trails, while large ones were cut up before removal, greatly increasing the costs of removing large litter items. The average time cost of removing a kilogram of litter was estimated at 3,359 ant-hours, and energy costs at 4.6 kJ. Colonies maintained trail systems 267 m in length and 16.5 m 2 in area, and built an estimated 2.7 km of trail with an area of 134 m 2 during a year. Based on litter standing crop and estimates of litterfall rates, total costs to colonies averaged 11,000 antdays of work and the energy equivalent of 8,000 leaf burdens. These costs are small relative to the number of available workers and rates of mass harvest, suggesting that costs do not significantly constrain trail construction. Instead, trails may persist because they provide access to high-quality resources or because only a few trails are required to fully exploit the foraging territory.

Individual and collective problem-solving in a foraging context in the leaf-cutting ant Atta colombica

“…The range of headwidth and fragment size we found in the experiments with the uncovered bridge is slightly smaller (Feener et al 1988;Shutler and Mullie 1991;Burd 1995) or very similar (Howard 2001) to that found in Weld studies on Atta colombica. Moreover, the correlation between load size and maximal headwidth is similar to that found by other authors (Shutler and Mullie 1991;Burd 1996).…”

Priority rules govern the organization of traffic on foraging trails under crowding conditions in the leaf-cutting ant Atta colombica

“…It remains to be seen whether, in the natural environment, trail widths are adjusted to optimize the net benefit of the trail, given the traffic demand, the cost of clearing (Howard, 2001) and the effect of traffic density on contact rates and information exchange. Indeed, according to our results, building wider foraging trails not only could be more costly but could also result in a lower foraging efficiency.…”

Allometric scaling of foraging rate with trail dimensions in leaf-cutting ants

“…Instead, they make physical transportation corridors as long as 200 m by cutting and clearing debris and vegetation along paths to foraging sites, and they maintain these pathways in the face of a rain of leaf litter [14]. These trails direct and restrict a colony's searching and foraging effort [15,16], so that essentially all resource movement occurs along these transportation corridors.…”

“…These trails direct and restrict a colony's searching and foraging effort [15,16], so that essentially all resource movement occurs along these transportation corridors. Trails carry the traffic of workers to and from leaf sources where ants harvest leaf tissue that is used as a substrate for their mutualist fungal gardens in the nest [14,17]. A colony's cumulative trail network used over the course of a year tends to form a highly branched pattern radiating in all directions from the central nest [18], although only one or a few minimally branching trails may be in active use on a given day.…”