9520835 FEENER Biological invasions provide excellent opportunities to study the organization of natural communities. This research uses Argentine ant invasions in northern California to test hypotheses concerning the causes of these invasions. The first objective is to quantify how different biotic and abiotic factors control the rate of invasions by conducting a natural trajectory experiment at 20 independent invasion fronts. These factors can be examined with unusual clarity because the invasion fronts of Argentine ants are well delineated and advance slowly. Of particular importance is determining if features of native ant communities govern the rate of spread of Argentine ants. The second objective is to determine the competitive mechanisms whereby Argentine ants displace native ants. Short-term introductions of Argentine ants at baits controlled by native ants will be used to examine mechanisms used by Argentine ants to supplant other species. In addition, the repellency of chemical defenses of the Argentine ants will be tested in laboratory experiments. Biological invasions are a common feature of most ecological communities. This study of invasion by Argentine ants should reveal competitive mechanisms that are common to other successful invaders, as well as some of the features governing invasion success in other natural communities.
