Canopy substrates influence foraging patterns in arboreal ant communities

Background/Question/Methods For cursorial central-place foragers such as ants, tropical forest canopies present abundant, plant-based carbohydrate resources embedded in a network of relatively linear substrates.  Consequently, arboreal ants forage and interact with each other on highly exposed pathways.  Here we examine how characteristics of two common canopy substrates—tree trunks and vine-like vegetation—influence foraging patterns of arboreal ants visiting patchy resources in a Costa Rican lowland wet forest.  We hypothesized that the relative speed of recruitment and body size distributions of foraging arboreal ants differ predictably among common substrate types.  We measured changes in ant abundance over time at tuna baits placed on bare tree bark, moss‑covered bark, and vine‑like vegetation appressed to bark.  We additionally examined the relationship between vine size (diameter) and forager size (body length) across a range of ant taxa, and quantified the effects of substrate roughness on foraging velocity in Crematogaster spp.  

Results/Conclusions Vine-like substrates reduced patch discovery time and recruitment time.  Experimental removal of vine and moss substrates nullified these differences, whereas addition of vine‑like substrates to trees naturally lacking vines had no effect on ant activity at baits.  Contrary to our expectations, body size showed a bimodal distribution on all three substrates, and there was no relationship between ant size and the diameter of vines they occupied while foraging.  Average running velocities for the fastest and slowest Crematogaster workers were significantly slower on coarse substrates, but the rugosity-velocity relationship was nonlinear.  Our results collectively indicate that linear substrates facilitate access of foraging ants to patchy resources and may have broader implications for competitive interactions.  Our ongoing studies in Panama extend these results to the community level by examining the effects of a large-scale liana removal/addition experiment on arboreal ant species richness and composition.