PARENT SESSION
Tuesday, August 8, 1:30-5:00 pm
COS 31 - Invasive species II: invasibility of communities and species invasiveness
Ballroom A, Ballroom Level, Cook Convention Center
Presiders: R Smith and S Jose

Community vulnerability to invasion by Argentine ants (Linepithema humile) is influenced more by fine-scale variation in the physical environment than by biotic resistance from native ants.

Menke, Sean^*,1, Holway, David, ¹ University of California, San Diego, San Diego, CA

ABSTRACT- Studies that test the importance of biotic resistance often implicitly assume that native and non-native species will respond in a similar manner to environmental variation. Argentine ant invasions provide an interesting system to examine how the importance of biotic resistance might be affected by large disparities in how native and introduced species differ with respect to key environmental tolerances. For example, we have previously demonstrated that in seasonally dry environments soil moisture controls the degree to which Argentine ants invade native ant communities, but that this physical factor is uncorrelated with native ant diversity. Here, we experimentally test the relative importance of biotic and abiotic factors in the invasion success of Argentine ants. In field manipulations involving added water and native ant removal, we found that (i) Argentine ants invaded all irrigated plots but none of the non-irrigated plots, (ii) Argentine ants were unable to invade non-irrigated plots from which native ants had been removed, (iii) an intact native ant community is able to slow but not prevent Argentine ant invasion at irrigated plots, and (iv) Argentine ants and certain native ant species responded positively to increased soil moisture. Our results provide a unique experimental demonstration of how relatively minor changes in physical conditions can far exceed competition from natives in determining invasion success. In addition, we demonstrate that L. humile and native ants responded heterogeneously to our manipulation of the physical environment. Interestingly, the two behaviorally dominant species, the native fire ant (Solenopsis xyloni) and the invasive Argentine ant, responded in a parallel manner to added water, whereas other native ants appeared largely unaffected by this treatment.

Key words: invasions, biotic resistance, ants