Extended phenotypes and foraging restrictions: ant nest entrances and resource ingress in leaf-cutting ants

Several factors may restrict the acquisition of food to below the levels predicted by the optimization theory. However, how the design of structures that animals build for foraging restrict the entry of food are less known. Using scaling relationships we determined whether the design of the entrances of leaf-cutting ant nests restricts resource input into the colony. We measured nests and foraging parameters in 25 nests of Atta cephalotes in a tropical rain forest. Ant flux was reduced to up to 60% at nest entrances. The width of all entrances per nest increased at similar rates as nest size, but the width of nest entrances increased with the width of its associated trail at rates below those expected by isometry. The fact that entrance widths grow slower than trail widths suggests that the enlargement of entrance holes does not reach the dimensions needed to avoid delays when foraging rates are high and loads are big. The enlargement of nest entrances appears to be restricted by the di...