PARENT SESSION
Oral Session #86: Invasive species: Ants and other invertebrates.
Presiding: J. Morrison
Thursday, August 8. 1:00 PM to 3:45 PM. Greenlee Meeting Room, TCC.
Colony structure variation and interspecific competitive ability in the invasive Argentine ant.
Holway, David*,1, Suarez, Andrew2, 1 Division of Biology (EBE), UC San Diego, La Jolla, CA2 Department of Environmental Science, Policy and Management, Berkeley, CA
ABSTRACT- Although the success of invasive species is often attributed to escape from natural enemies and competitors, changes in the ecology or behavior of invaders that occur following establishment may also be important. Argentine ants (Linepithema humile) are of interest in this respect: introduced populations almost completely lack intraspecific aggression, whereas in native populations intraspecific aggression is common. We employ three approaches to examine how such variation might influence the interspecific competitive ability of the Argentine ant. We conducted a lab experiment involving pairs of Argentine ant colonies that either did or did not exhibit intraspecific aggression and that were reared with colonies of Forelius mccooki, an aggressive competitor. Unlike intraspecifically aggressive pairs, all non-aggressive pairs fused during the experiment. Non-aggressive pairs also foraged more actively during the experiment and supported more workers and produced more eggs relative to aggressive pairs. Compared to Forelius colonies reared with intraspecifically aggressive pairs, those reared with non-aggressive pairs produced fewer brood, foraged less actively, and supported fewer living workers. Short-term field experiments corroborated lab findings. At natural contact zones between L. humile and Forelius, the introduction of lab colonies of Argentine ants that fought with conspecific field colonies caused this species to abandon baits in the presence of Forelius, whereas the introduction of lab colonies that did not fight with field colonies of Argentine ants resulted in their retaining possession of baits. Additional supportive evidence for this hypothesis comes from the native range. At a site along the Rio Parana, we found that the density of Argentine ants was inversely related to the diversity and abundance of other ant species. These results illustrate that colony structure variation can influence interspecific competitive ability and provide further experimental support for how the loss of intraspecific aggression influences the success of the Argentine ant as an invader.
KEY WORDS: biological invasion, Argentine ant, interspecific competition, intraspecific aggression