Branching angles reflect a trade‐off between reducing trail maintenance costs or travel distances in leaf‐cutting ants

Abstract

The design of transport paths in consuming entities that use routes to access food should be under strong selective pressures to reduce costs and increase benefits. We studied the adaptive nature of branching angles in foraging trail networks of the two most abundant tropical leaf-cutting ant species. We mathematically assessed how these angles should reflect the relative weight of the pressure for reducing either trail maintenance effort or traveling distances. Bifurcation angles of ant foraging trails strongly differed depending on the location of the nests. Ant colonies in open areas showed more acute branching angles, which best shorten travel distances but create longer new trail sections to maintain than a perpendicular branch, suggesting that trail maintenance costs are smaller compared to the benefit of reduced traveling distance. Conversely, ant colonies in forest showed less acute branching angles, indicating that maintenance costs are of larger importance relative to the benefits of shortening travel distances. The trail pattern evident in forests may be attributable to huge amounts of litterfall that .increase trail maintenance costs, and the abundant canopy cover that reduces traveling costs by mitigating direct sunlight and rain. These results suggest that branching angles represent a trade-off between reducing maintenance work and shortening travel distances, illustrating how animal constructions can adjust to diverse environmental conditions. This idea may help to understand diverse networks systems, including urban travel networks.

Integrating the host plant phylogeny, plant traits, intraspecific competition and repeated measures using a phylogenetic mixed model of field behaviour by polyphagous herbivores, the leaf-cutting ants

“…We found that the PGLS model captured essential features of LCA foraging behaviour, including the effects of tree size and distance to the colony (Costa et al . 2018, Farji-Brener et al . 2015, Kost et al .…”

“…Up to now, most studies on leaf-cutting ant foraging have focused on testing specific well-defined hypotheses about how host plant properties affect ant behaviours, These have included tree size, the distance from colony to the foraging patch, as well as different measures of leaf characteristics (Farji-Brener et al . 2015, Rocha et al .…”

Unpaved roads alter foraging patterns of the leafcutter antAtta colombica

“…For leafcutter ants, trail building and maintenance are a major energy cost for resource acquisition (Lugo et al 1973;Lewis et al 2008;Farji-Brener et al 2014). The energy invested into resource acquisition is generally balanced against the nutrient value of a resource (optimal diet theory; Rockwood & Hubbell 1987), and thus the trade-off between trail-building costs and resource nutritional value has been hypothesized to partially govern foraging in leafcutter ants (Shepherd 1985;Rockwood & Hubbell 1987).…”

“…Email: mewinsto@uchicago.edu Studies on Neotropical Fauna and Environment, 2015http://dx.doi.org/10.1080/01650521.2015 colonies (Vasconcelos et al 2006). In light of research that has estimated trail maintenance as 75% of the total energetic costs of the colony (Lugo et al 1973), and other work that has shown leafcutters respond to specific environmental conditions to optimize performance (Lewis et al 2008;Farji-Brener et al 2014), it is possible that leafcutter foraging in disturbed habitat differs from that in undisturbed, old growth forest. Conversely, estimation of foraging costs by Howard (2001) suggests the costs of trail maintenance to be minimal relative to the number of available workers and the rates of mass harvest.…”

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

“…The building of trail branches generates a conflict between shortening travel distances and reducing trail maintenance work (Farji‐Brener et al . ). However, there is little information on whether nest entrances are also subjected to ecological trade‐offs that may restrict the input of food into the colony.…”