Distribution of the introduced Argentine ant (Iridomyrmex humilis) in natural habitats of the lower Sacramento Valley and its effects on the indigenous ant fauna

Abstract

Of 4 natural habitats surveyed (valley riparian woodland, foothill riparian woodland, blue oak-digger pine woodland, and chaparral) in Yolo and Solano counties only valley riparian woodland was colonized by I. humilis. Sites occupied by I. humilis have permanent sources of water and tend to be environmentally degraded. Patches of semidisturbed riparian woodland provide refuges from which populations of I. humilis may invade adjacent agricultural land, and vice versa. The species richness of native ants is markedly reduced at riparian woodland sites occupied by I. humilis. Among the common native ants, epigaeic species are more susceptible to displacement by I. humilis than are hypogaeic species. The most adversely affected species (Liometopum occidentale, Tapinoma sessile, Formica occidua), absent from sites colonized by I. humilis, are dominant epigaeic ants: 2 of the 3 least displaced species (Stenamma diecki, S. californicum) are timid, cryptobiotic ants that forage in soil and leaf litter. -from Author