Pruning of host plant neighbors by ants: an experimental approach

Some ants of myrmecophytic plants either obligately or facultatively prune vegetation surrounding their host trees. Pruning behavior occurs at higher frequency in ants with sting defenses than in those with chemical defenses, which may generally convey an advantage in aggressive encounters between ants. Experiments in tropical moist forest of Peru tested the hypothesis that pruning may reduce the threat of invasions by potentially dangerous alien ants. When unseverable contacts were made between Triplaris americana 1-3 m in height and neighboring plants, Crematogaster ants invaded more frequently and in greater numbers than on control plants and inhibited activities of behaviorally subordinate resident Pseudomyrmex dendroicus. Invaders occasionally carried away brood and usurped hollow stem nests of resident ants. Pseudomyrmex cut petioles of leaves on plants contacting their hosts as well as leaves of their own host plants, when these leaves formed bridges for major invasions. Basal clearings maintained by Pseudomyrmex around their hosts appear to reduce the likelihood that Crematogaster workers will occur in the vicinity of the tree trunk. On Cordia nodosa inhabited by Allomerus demararae, numbers of invading ants did not differ on experimental and control trees, perhaps because larger ants cannot invade through dense trichomes. Allomerus workers attacked encroaching vines only when these vines bore large numbers of Crematogaster.