Nonindigenous Ants Associated with Geothermal and Human Disturbance in Hawai'i Volcanoes National Park

Although the Hawaiian Islands lack indigenous ants, more than 40 exotic species have become established there, primarily in lowland areas, where they have been implicated in the extermination of much of the endemic Hawaiian fauna. In June to August 1994, I surveyed ants in the K.I1auea Caldera region (elevation 1090-1240 m) of Hawai'i Volcanoes National Park to evaluate the current range and potential impact of ants in this protected montane ecosystem. Ants were common in areas disturbed by geothermal or human activity, but rare in undisturbed forest. A total of 15 ant species was collected, including 10 "lowland" ant species that are generally restricted to elevations below 900 m in Hawai'i. Pheidole megacephala and Anoplolepis longipes, major pest species in lowland Hawai'i, occurred in very high densities in and around the geothermal area near the park headquarters. Paratrechina bourbonica and Cardiocondyla venustula, two cold-tolerant species, were the most common ants in a second geothermal area, the Puhimau hot spot, and in areas disturbed by human activity, including roadsides. Linepithema humile, a major pest species in drier highland areas, occurred only in and around park buildings. The geothermal areas and park buildings appear to serve as warm "habitat islands" that allow Ph. megacephala, A. longipes, and other lowland ants to extend their ranges to higher elevations. Colonization of geothermal areas by lowland ant species, such as Ph. megacephala and A. longipes, poses a threat to endemic Hawaiian species in those areas. Colonization of roadsides and other disturbed areas by more cold-tolerant ants, such as P. bourbonica, C. venustula, and L. humile, poses a more general threat to endemic Hawaiian species found at higher elevations