Print PageIn tropical rain forests, arboreal ants often depend on plants for both food and shelter. However, the plant foods most commonly available to ants tend to be carbohydrate-rich, but nitrogen-poor. To compensate for nitrogen limitation, arboreal ants may either supplement their diets with insect prey or associate with microbial symbionts that are thought to provision their hosts with essential amino acids. Nevertheless, low-N plant foods often make up the largest portion of the diet of many tree-dwelling ants and it is not clear to what extent they depend on the insect herbivores that visit plants to satisfy their nitrogen requirements.
We investigated the contribution of insect prey to the diet of the tropical arboreal ant Allomerus octoarticulatus. We maintained A. octoarticulatus colonies nesting in Cordia nodosa trees in herbivore exclosures and control treatments for nearly a year and then compared the behaviour, morphology, and fitness of ant colonies in the two treatments. We measured ant colony growth over the course of the experiment, and measured the size and dry weight of A. octoarticulatus workers after 11 months. At the end of the experiment, we also compared ant recruitment to protein-rich versus carbohydrate-rich baits in a preference assay.
Results/Conclusions
We found that ants that developed in herbivore exclosures had a stronger preference for protein-rich over carbohydrate-rich baits than ants in the control (i.e., herbivores present) treatment. Furthermore, workers in the control treatment were slightly larger and heavier than in the herbivore exclosure treatment, but ant colony growth did not differ between the treatments. Therefore, when ant colonies were restricted to a mostly plant-based diet, they foraged more intensely for protein-rich foods, but overall colony performance was not affected. To shed more light on the results of this experiment, we are currently investigating the microbial assemblages in the guts of A. octoarticulatus workers.
