EFFECTS OF ABIOTIC FACTORS ON THE DISTRIBUTION AND ACTIVITY OF THE INVASIVE ARGENTINE ANT (HYMENOPTERA, FORMICIDAE)

The Argentine ant, Linepithema humile (Mayr). has spread worldwide, of ten decimating native ant populations and other arthropod species in i nvaded, areas. It is not known what abiotic and biotic conditions limi t its distribution. We investigated the distribution of the Argentine ant in the Jasper Ridge Biological Preserve in northern California a n ature preserve that has been partially invaded by these ants. Canonica l correlation analysis showed that the Argentine ant is most likely to occur near the edges of the preserve, which are next to disturbed are as and in low-elevation areas. Native ant species are associated with higher-elevation areas farther from the presence edge. Distance to sur face water and insolation were less important in predicting Argentine ant distribution. This suggests that dispersal from disturbed areas st rongly determines the spread of the invasion. We examined how the dail y activity patterns of Argentine ants and several native ant species d epend on soil temperature, air temperature, and relative humidity. The re was considerable overlap in activity times, and there were no value s of ally of the abiotic factors measured in which native ant species were more likely to be active than Argentine ants. Because the Argenti ne ant is usually active at the same times as any native species, most native species in invaded areas are likely to encounter the invaders frequently. Diet overlap was high with most native ant species except for seed-eating species. Overlap in activity times may intensify both exploitative and interference competition between the Argentine and na tive ant species.