Influence of the Hypogaeic Army Ant Dorylus (Dichthadia) laevigatus on Tropical Arthropod Communities

The majority of army ant species forage hypogaeically. Due to the difficulties in observing these ants, their potential influence on hypogaeic and epigaeic arthropod communities has not yet been investigated. As the first hypogaeically foraging army ant studied in detail, we attracted Dorylus laevigatus to areas monitored for their arthropod diversity. Here, for the first time, the same sites were sampled before and after an army ant raid. Furthermore, interactions between D. laevigatus and the five most common ground-nesting ant species were noted and their life-history traits compared, allowing first inferences on possible mechanisms of their coexistence. The occurrence of D. laevigatus within a study plot had no evident effect on the number of arthropod taxa or individuals collected with epigaeic and hypogaeic pitfall traps. Likewise, juvenile arthropods, which are less mobile and thus are potentially easier prey for D. laevigatus, showed no differences in their collected numbers before and after the army ant had visited a plot. However, significantly fewer ant species were collected with hypogaeic traps after D. laevigatus had been within the study plots, indicating a possible predation of D. laevigatus especially on two Pseudolasius and one Pheidole species. The five most common ground-foraging ant species demonstrated their ability to avoid, kill, and even prey on the army ant. The reaction of Lophomyrmex bedoti towards D. laevigatus indicated the former to be a potential prey species, while Pachycondyla sp. 2 showed signs of "enemy specification." Odontoponera diversus and O. transversa actively preyed on D. laevigatus, while Pheidologeton affinis fought with D. laevigatus over resources. All ant species could co-occur with D. laevigatus at palm oil baits. Adding to the differences detected in previous studies between D. laevigatus and epigaeically foraging army ant species, the occurrence of this hypogaeic army ant seems to have less devastating effects on arthropod community compositions than those of epigaeically mass raiding species.