Effects of the Argentine Ant on Arthropod Fauna of Hawaiian High‐Elevation Shrubland

Abstract

Human—caused biological invasions by an alien species are a worldwide phenomenon. They are particularly significant on isolated oceanic islands and represent a serious threat to endemic biota. The Argentine ant (Iridomyrmex humilis) has become established in portions of the high—elevation shrubland of Haleakala National Park, Maui, Hawaii, over the past 25 yr. This ecosystem lacks native ants but possesses many locally endemic and rare anthropod species. Pitfall trapping and under—rock surveys were conducted to determine the effects of I. humilis on the local arthropod fauna. More than 180 taxa were sampled, mostly Arthropoda. Presence of the Argentine ant is associated with reduced populations of many native and non—native anthropod species, including important predator species and major pollinators of native plants. Effects of ant invasion were particularly severe at higher elevations of Haleakala volcano where endemic species normally exist at low densities. Some taxa, primarily alien species, were more abundant in the presence of ants. Invasion of the Argentine ant has locally reduced the abundance of many endemic species in the shrubland ecosystem. Although the spread of this ant species is slow, I. humilis appears to have the potential to invade a much larger area of Haleakala National Park than it now occupies. Active management of Argentine ant populations will be necessary if the endemic fauna is to be preserved.

Relative risk of invasive ants (Hymenoptera: Formicidae) establishing in New Zealand

“…ants do not forage during heavy rain, and in high rainfall areas foraging time is reduced and possibly so also is the probability of establishment (cole et al 1992;Vega & Rust 2001). in high rainfall areas it may be the permeability of the soil and the availability of relatively dry areas to nest that limits distribution, rather than rainfall per se (chen et al 2002).…”

Bait Preference by the Argentine Ant (Hymenoptera: Formicidae) in Haleakala National Park, Hawaii

“…Because ants were absent from this evolutionary process, nothing with their predatory capability helped shape native arthropod defense mechanisms. The consequent vulnerability of native arthropods to ant predation has been well documented (Perkins 1913, Cole et al 1992, Gillespie and Reimer 1993.…”

“…Typically, the effects of alien ants have been limited to sea level and lowland areas of the islands, but the Argentine ant, Linepithema humile (Mayr), differs in that it has become established at higher elevations, and therefore has invaded largely intact natural areas such as Haleakala National Park on Maui (Cole et al 1992). Not only do these higher elevation populations put L. humile into mostly undisturbed native habitat, but they also take it out of the range of other dominant alien ants.…”

“…In Haleakala National Park, Cole et al (1992) have demonstrated the effects of the ant's presence and predation on the native arthropod fauna, and they have suggested that this could have an impact on native plant reproduction, as some of the affected insects are major pollinators of native plants.…”

“…Despite rather extreme climatic conditions on upper Haleakala, the Argentine ant has been able to persist, reproduce, and expand. In fact, by the mid-1980s, 2 distinct populations have become established at 2 different elevations on Haleakala's upper western slopes (Medeiros et al 1986, Cole et al 1992, and by 1995-1996 the ant had occupied >450 ha of the park and surrounding areas.…”