Indirect effects of ant eradication efforts on offshore islets in the Hawaiian Archipelago

Abstract

Invasive species eradication and control are considered vital components of the conservation, restoration, and management of many native ecosystems. Invasive ants, which are notoriously difficult to eradicate, can cause catastrophic changes in ecosystems and are aggressive colonists. Here we report the eradication and control of two widely distributed invasive ants and subsequent unanticipated effects on arthropod and avian communities. We used a paired experimental design that included 1 year of baseline data collection, to test the effects of the formicide hydramethylnon on abundances of two ant species on two pairs of offshore islets. Pheidole megacephala was eradicated from the treated islet in pair 1 and was not detected during 2003-2008. On pair 2 Solenopsis geminata numbers declined, but the species remained present. Target ant densities remained high on untreated islets. Application of hydramethylnon reduced numbers of alien cockroaches (Order: Blattaria), but we did not detect effects on other nontarget arthropods. The eradication of P. megacephala was followed by dynamic compositional changes in the ant community, including the apparent colonization by three species (S. geminata, Tetramorium bicarinatum and Anoplolepis gracilipes) previously undetected on the islet. One of these, A. gracilipes, underwent a rapid range expansion during 2006-2008 which corresponded with reduced seabird nesting success. We conclude that hydramethylnon can be used effectively to eradicate P. megacephala. However, ant eradications can have detrimental effects on ecosystems and the potential for subsequent colonization of sites by other ant species that may be more harmful and more difficult to eradicate needs to be considered.

The hitchhiker’s guide to alien ant invasions

“…Hoffmann (2010) reported a complete recovery of native ants after eradication of P. megacephala in northern Australia, whereas Plentovich et al (2011) observed colonization by other invasive species after eradication of P. megacephala on small offshore islets in the Hawaiian archipelago. Natural succession and re-colonization, however, is often hampered by the severity of modification inflicted by the invader.…”

Invasive ants influence native lizard populations

“…An additional explanation for our finding that RIFAs did not influence fence lizard survival is that Amdro, although largely targeted to control RIFAs, can reduce native ant and orthoptera populations (Plentovich et al. ). Ants comprise a large proportion of the fence lizard diet (approximately 80% in juveniles), though other invertebrates (e.g., Orthoptera) make a considerable contribution (Hamilton and Pollack , DeMarco et al.…”

High invasive ant activity drives predation of a native butterfly larva

“…], Hawai'i [Plentovich et al . ]), which may be more susceptible to effects of invasive species than continental ecosystems (Simberloff ). Only one published study has investigated effects of A. gracilipes on invertebrate communities on mainlands, and it found no significant effect of A. gracilipes on the abundance or richness of ground invertebrates (Hoffmann & Saul ).…”