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

Abstract

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 restricts the entry of food is 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 digging effort required to enlarge nest tunnels and by increments in the risk of inundation, predator/parasitoid attacks and microclimate imbalances inside the nest. The design of the extended phenotypes can also restrict the ingress of food into the organisms, offering additional evidence to better understand eventual controversies between empirical data and the foraging theory.Abstract in Spanish is available with online material.

Morphological determinants of bite force capacity in insects: a biomechanical analysis of polymorphic leaf-cutter ants

“…they render them less generalist. For example, the increased head size may reduce mobility at the nest entrance and within the nest where small heads may be beneficial to successfully manoeuvre through the close-knit structure of the fungal garden (figure 3 f ; [69]). Indeed, significant numbers of larger workers typically only exist in colonies which exceed a minimum size [14], consistent with the hypothesis of specialized large workers but generalist small workers.…”

Why are antlion larvae rare under the leaf litter? Testing the hypothesis of improper trap maintenance

“…In semi‐sedentary organisms, establishment in unfavourable sites should be penalised by natural selection because its relocation capacity is energetically costlier and limited compared to more mobile animals (Pinter‐Wollman & Brown, 2015; Scharf & Ovadia, 2006). For example, leaf‐cutting ant nests are rare in floodable sites because these areas negatively impact leaf‐cutting foraging and survivorship (Farji‐Brener et al, 2018; Rodríguez‐Planes & Farji‐Brener, 2019; Sendoya et al, 2014). Therefore, semi‐sedentary organisms can be considered optimal subjects to study the causes of habitat avoidance and thus, to improve our understanding of the mechanistic basis of habitat selection (Lubin et al, 1993; Morris, 2003).…”

Multiple nest entrances alter foraging and information transfer in ants

“…In addition, because most of the ants located close to the nest openings are oriented towards the incoming foragers, the entrance area acts as a front line where information about environmental opportunities can be first processed and easily updated by nest-mates [29]. At this particular hotspot for information transfer, it has been demonstrated that the rate at which recruits leave the nest depends on the rate at which successful foragers carry food and provide antennal contacts [15][16][17]26], but also on the design of the entrance [30]. In this respect, the number of nest entrances may shape the food recruitment process by segregating the information flow, thus altering the encounter rates that are locally experienced by potential recruits inside the nest.…”