Effects of Argentine Ants on Invertebrate Biodiversity in Northern California

Although most biological invasions usually fail (Elton 1958; Simberloff 1981; Lodge 1993), some invasive species can change the composition and function of communities and ecosystems through competition, predation, and habitat alteration (Elton 1958; Simberloff 1981; Mooney & Drake 1986; Drake et al. 1989; Vitousek 1990). The effects of invasive ant species on native ant fauna have been described in many systems (Foster 1908; Crowell 1968; Haskins & Haskins 1965, 1988; Erickson 1971; Tremper 1976; Haines & Haines 1978; Clark et al. 1982; Lubin 1984; Medeiros et al. 1986; Ward 1987; Porter et al. 1988; De Kock 1990; Porter & Savignano 1990; Cole et al. 1992; Holway 1995). Most of these studies have reported striking declines in the abundance and species richness of native ants in areas invaded by exotic ant species, although particular groups of ants occasionally coexist with the invaders (Haskins & Haskins 1965, 1988; Ward 1987). The effects of invasive ants on non-ant invertebrates have been less extensively studied than effects on other ant species. Invertebrate displacement by invasive species could have cascading effects on ecosystems because many invertebrates play important roles in ecosystem processes. Moreover, understanding how broad classes of organisms are associated with an invasive species can provide insight into the mechanisms of invasion and displacement. We compare the composition of invertebrate communities in areas invaded and uninvaded by the Argentine ant ( Lipepithema humile ). The Argentine ant is native to South America, and it is an increasingly common invasive species world-wide (Ward 1987; Holway 1995; Human & Gordon 1996). Methods