The role of competitive dominance in the invasive ability of the Argentine ant (Linepithema humile)

To assess the importance of competition in the advance of invasive species, bait stations have been used to determine the dominance hierarchy of a community of native ants in Doñana National Park, southern Spain, and the status of the introduced species Linepithema humile (Argentine ant). Some native species, e.g. Cataglyphis floricola or Camponotus pilicornis, seem to be subordinate, i.e. occupy a low position in the competitive hierarchy; some are dominant (e.g. Pheidole pallidula), and others (e.g. Aphaenogaster senilis) occupy an intermediate position in the hierarchy. The Argentine ant is a competitively dominant species, because of its aggressive behavior and relative abundance. Irrespective of their position in the dominance hierarchy, L. humile and some native species adopt what games theory terms “the bourgeois strategy” during agonistic encounters with other species. Lone workers tend to be submissive in encounters whereas workers in the presence of other colony members are aggressive. L. humile was the only species which aggressively displaced large numbers of ants of other species from the bait. L. humile also expanded its range in the course of the experiment, displacing native species from parts of the study area.