Invasion of Red Imported Fire Ants (Hymenoptera: Formicidae): Microgeography of Competitive Replacement

The invasion of Brackenridge Field Laboratory, Austin, Texas, by the multiple-queen form of the red imported fire ant, Solenopsis invicta Buren, was monitored for 3 yr. This invasion provides a rare glimpse of competitive replacement in progress. It has been remarkable for two reasons. First, imported fire ant colonies replaced colonies of the native fire ant, Solenopsis geminata (F.), at a ratio of 6:1, indicating a radical restructuring of the arthropod community rather than a simple one-for-one substitution of an equivalent species. Secondly, the invasion proceeded at a very slow rate (about 35 m/yr) along a continuous front in a pattern best explained by colony budding and considerable biotic resistance from the native ant community. These data indicate that the invasion process may continue at the local level for years or even decades after the passage of the main invasion front.