Argentine ant (Linepithema humile) distribution along urban and riparian interfaces in southern California

The Argentine ant (Linepithema humile) is a widespread invasive species whose spread has been largely linked to abiotic variables. I documented the distribution of L. humile with respect to an urban edge and riparian corridor at two sites in southern California. I attempted to link their distributions to relative humidity, temperature, and soil moisture; variables often cited as possible predictors of invasion. I also tested for associations between L. humile and other ant species. I studied the interplay between soil moisture and humidity levels in Argentine ant survival and reproduction in a laboratory experiment. Argentine ants were more abundant near the urban and riparian interface as predicted, although this relationship was not consistent. Temperature, relative humidity or soil moisture did not correlate with their distributions. Contrary to expectations, the majority of ant species were independently distributed with respect to L. humile. In the laboratory, L. humile worker survival was greater in humid habitats with ample soil moisture as compared to dry conditions. More eggs were laid in humid habitats than dry indicating an increase in reproduction under high humidity.