Foraging in highly dynamic environments: leaf-cutting ants adjust foraging trail networks to pioneer plant availability

Major shifts in the availability of palatable plant resources are of key relevance to the ecology of leaf-cutting ants in human-modified landscapes. However, our knowledge is still limited regarding the ability of these ants to adjust their foraging strategy to dynamic environments. Here, we examine a set of forest stand attributes acting as modulating forces for the spatiotemporal architecture of foraging trail networks developed by Atta cephalotes L. (Hymenoptera: Formicidae: Attini). During a 12-month period, we mapped the foraging systems of 12 colonies located in Atlantic forest patches with differing size, regeneration age, and abundance of pioneer plants, and examined the variation in five trail system attributes (number of trails, branching points, leaf sources, linear foraging distance, and trail complexity) in response to these patch-related variables. Both the month-to-month differences (depicted in annual trail maps) and the steadily accumulating number of trails, trail-branching points, leaf sources, and linear foraging distance illustrated the dynamic nature of spatial foraging and trail complexity. Most measures of trail architecture correlated positively with the number of pioneer trees across the secondary forest patches, but no effects from patch age and size were observed (except for number of leaf sources). Trail system complexity (measured as fractal dimension; Df index) varied from 1.114 to 1.277 along the 12months through which ant foraging was monitored, with a marginal trend to increase with the abundance of pioneer stems. Our results suggest that some leaf-cutting ant species are able to generate highly flexible trail networks (via fine-tuned adjustment of foraging patterns), allowing them to profit from the continuous emergence/recruitment of palatable resources.