Ant communities are thought to consist of a competitive hierarchy of interacting species, with an assemblage of subordinate species being structured by a dominant species. Mensurative and behavioral studies suggest a significant role for competition in structuring ant communities, although there are few experimental studies to support this contention. We examined the effect of the dominant ant Iridomyrmex purpureus on the ant fauna of sandstone outcrops in southeastern Australia. We conducted a mensurative survey using transect counts to compare ant assemblages at eight outcrops with, and eight without I. purpureus. Using cages, we then successfully excluded the dominant ant from four outcrops and compared assemblages at these exclusion sites with those at sites with and without I. purpureus and with procedural control sites over a period of 12 months. We conducted behavioral studies comparing I. purpureus with six other common species in terms of their abilities to locate, recruit to, and defend bait. While initial surveys indicated both positive and negative effects of I. purpureus on the activity of several subordinate species, exclusion of I. purpureus resulted only in changes in the abundance of other species of Iridomyrmex, which are behaviorally and ecologically similar to the dominant species. Iridomyrmex purpureus was faster at discovering bait than other species, but not always better at recruiting to the bait. It interfered with the foraging of all species tested; however, it displaced other Iridomyrmex from bait most often. While longerâterm studies may provide more definitive results, exclusion of the dominant species over one year had strong effects only on ecologically similar species. Despite its behavioral dominance and association with several other species in the mensurative surveys, I. purpureus was not shown to cause any other major changes in ant community structure.