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The effect of a dominant ant, Iridomyrmex purpureus, on resource use by ant assemblages depends on microhabitat and resource type


* Present address: Department of Animal Ecology, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden (Email:


Abstract  Behaviourally and ecologically dominant ants are thought to structure ant communities through their monopolization of resources. Effects of a dominant ant, Iridomyrmex purpureus, on resource use by ant communities were tested using an exclusion experiment on sandstone outcrops near Sydney, in south-eastern Australia. The success of functionally different ants at honey and mealworm baits placed in rock and vegetation microhabitats was measured in a series of surveys before and after exclusion. I. purpureus was successfully excluded from the outcrops and patterns of resource use following I. purpureus exclusion were consistent with those of sites without I. purpureus and procedural control sites. At sites with I. purpureus, resources were discovered more rapidly, however, other ants were less successful, particularly on rock substrates. Iridomyrmex spp. were more successful on rock than in vegetation, however, in the presence of I. purpureus, the success of other Iridomyrmex on rock substrates and at honey baits was reduced. Camponotine and myrmicine ants had low success at baits and tended to be less successful in the presence of I. purpureus. In contrast, the opportunist Rhytidoponera metallica was not affected by the presence of I. purpureus and was more successful in the vegetation habitat. These findings indicate that the dominant ant affects the success of other ants at baits, particularly the ecologically similar Iridomyrmex. However, effects of I. purpureus on other taxa differ between habitats differing in complexity and resources differing in composition and defensibility.