Experimental confirmation of competition between two dominant species of Iridomyrmex (Hymenoptera: Formicidae)

The well-defined ant succession following disturbance of coastal heathland in eastern Australia includes community replacement triggered by one dominant species of Iridomyrmex (species C) being replaced by another (species A). This paper investigates the consequences of experimentally reducing the abundance of species A by injecting petrol into the nest entrances of colonies. The response of species C was monitored at 2 and 10 months after removal and shows highly significant increases in the number of pitfall traps occupied and the area of territory maintained by this species. It is confirmed that interspecific competition plays an important role in maintaining the observed mosaic pattern of ant distribution and is also important in ant succession. The mechanism of competition is interference or, more exactly, territorial competition. The species appear to actively defend territorial space by patrolling territory boundaries that are breached when the defenders are eliminated.