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.

A predator‐proof fence was built at Kaena Point Natural Area Reserve, Hawaii in 2010 as part of an ecosystem restoration project. All non‐native mammalian predators were removed and are now excluded. Non‐native plants are being removed and native species are being outplanted. We monitored abundance and reproduction of Puffinus pacificus (wedge‐tailed shearwaters), collected soil samples before and after fence construction, and examined the relationship between changes in shearwater numbers and soil nutrients. Shearwater numbers increased over time, from 11 young produced in 1994 to 3,274 in 2012. The average number of shearwaters produced during the 3 years before and after fence construction increased from 614 ± 249 to 2,359 ± 802 (384% increase). The average number of shearwater pairs attempting to nest also increased during the same periods, from 3,265 ± 827 to 4,726 ± 826 (45% increase). Soil samples from 2010 to 2013 showed an overall decline in concentration of ammonium (NH4+) and no change in concentration of nitrate (NO3−) or orthophosphate (PO43−). However, there was a positive relationship between changes in shearwater numbers and changes in ammonium. Examination of spatial patterns in nutrient abundance showed that the highest nutrient concentrations occurred in areas dominated by the non‐native nitrogen‐fixing plants Leucaena leucocephala and Prosopis pallida. Removal of these plants caused local nutrient declines, but increases in shearwater numbers have countered this at some points. We anticipate that shearwaters and other seabirds will replace non‐native plants as the dominant source of nitrogen and phosphorous and facilitate recovery of a native‐dominated plant assemblage.

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