Drivers of variation in yellow crazy ant ( <i>Anoplolepis gracilipes</i> ) abundance and impacts on native fauna in an atoll ecosystem

Abstract The yellow crazy ant ( Anoplolepis gracilipes ; YCA) is a widespread invader of islands across the Pacific and Indian oceans. This species can negatively affect native fauna and, at high abundances, ecosystem functions. Here we investigated the activity patterns, habitat preferences, and impacts of YCA on a Polynesian atoll (Teti'aroa). We found that YCA activity decreases with increasing substrate temperature, and that YCA favored substrates rich in coarse woody debris and Pisonia grandis trees. By comparing 46 sites varying in YCA abundance (including on non‐invaded islets) we found that ground nesting seabird (brown noddy, Anous stolidus ) presence and abundance decreased with increasing YCA abundance. Terrestrial hermit crab abundance also varied relative to YCA abundance; YCA abundance was negatively correlated with the presence of Coenobita perlatus and positively correlated with the presence of Coenobita rugosus (apparently due to a shared habitat preference for woody debris) and Coenobita brevimanus (potentially due to a shared preference for Pisonia forest). These impacts occurred despite the relatively low abundance of YCA during our surveys. In addition to identifying some drivers of variation in YCA abundance, this study provides an example of how YCA can impact the fauna of atoll islets with ground nesting seabirds. YCA control or eradication measures may be required in order to restore healthy seabird and terrestrial crab populations in this context.