Ecology of some lesser-studied introduced ant species in Hawaiian forests

Abstract

Invasive ants can have strong ecological effects on native arthropods, but most information on this topic comes from studies of a handful of ant species. The ecological impacts of the many additional introduced 'tramp' ant species are largely unknown. In mesic upland forests of O'ahu, Hawai'i, ten species of introduced ants were found on four species of understory trees. However, these ants were generally uncommon and occurred at relatively low densities in this habitat type. The most common and abundant ant was Plagiolepis alluaudi, which favored the native tree Pipturus albidus. Ecological effects of ants on arthropods were found to be modest, with overall arthropod community composition not significantly different between ant-occupied and ant-free trees. Most taxonomic groups were similar in abundance and richness between ant-occupied and ant-free trees, except adventive Coleoptera, adventive Hemiptera, and Lepidoptera were less abundant on ant-occupied trees, and adventive Coleoptera and adventive Hemiptera also had lower richness on ant-occupied trees. Among Lepidoptera, caterpillars of two endemic groups had significantly lower incidences on trees with higher ant abundances, while other caterpillars did not. Arthropod trophic structure was largely unaffected, except that chewing herbivores comprised a smaller fraction of biomass on ant-occupied trees. While overall ecological effects were weak in comparison to prior results involving other ant species in Hawai'i, some of the impacts suggest that higher densities of these introduced ant species could result in similar interactions with arthropods as those of the better-studied invasive ant species.

Plagiolepis alluaudi Emery, 1894, a globally spreading exotic ant (Hymenoptera, Formicidae) newly recorded from Tenerife (Canary Islands, Spain)

“…Most exotic ants are not imposing threats to native ecosystems and only a relatively small subset of species can establish outside disturbed areas (McGlynn 1999;Holway et al 2002). However, P. alluaudi has in several places spread into relatively undisturbed forests, for example in Hawaii, where it is now the most common ant species in some areas (Krushelnycky 2015).…”

“…Being a generalist forager that frequently tends Hemiptera for honeydew (Smith 1957;Krushelnycky 2015), it can live in mutualistic association with many honeydew producers (compare Staab et al 2015), many of which are also exotic and can facilitate the ecological success of exotic ants (Lach 2003). Thus, in case P. alluaudi will become established in native habitats, it may compete with native ants for resources.…”

Alien Species and Insect Conservation

“…Krushelnycky ( 2015 ) noted a total of nearly 60 introduced ant species, and found 10 of these on understorey trees in the mesic forests of Oahu. For Hawai'i.…”

Alien Insects and Insect Conservation

“…For Hawai'i. Krushelnycky ( 2015 ) noted a total of nearly 60 introduced ant species, and found 10 of these on understorey trees in the mesic forests of Oahu. Only about a third of his 384 samples included ants, and fewer than 10 % had fi ve or more individuals.…”