Invasive ants compete with and modify the trophic ecology of hermit crabs on tropical islands

*[Here, we demonstrate how the trophic ecology of the remote atoll nation of Tokelau is changing due to competition between the invasive ant, Anoplolepis gracilipes, & native terrestrial hermit crabs, Coenobita spp., for carrion. A significant negative correlation was observed between A. gracilipes & hermit crab abundance. On islands with A. gracilipes, crabs were generally restricted to the periphery of invaded islands. Very few hermit crabs were found in central areas of these islands, where A. gracilipes abundances were highest. Ant exclusion experiments demonstrated that changes in the abundance & distribution of hermit crabs on Tokelau are a result of competition. The ants did not kill the hermit crabs. Rather, when highly abundant, A. gracilipes attacked crabs by spraying acid, driving crabs away from carrion resources. Analysis of naturally occurring N and C isotopes suggests that the ants are effectively lowering the trophic level of crabs. According to delta-15N values, hermit crabs have a relatively high trophic level on islands where A. gracilipes have not invaded. In contrast, where these ants have invaded, we observed a significant decrease in delta-15 N for all crab species. This result concurs with our experiment in suggesting long-term exclusion from carrion resources, driving co-occurring crabs towards a more herbivorous diet. Changes in hermit crab abundance or distribution may have major ramifications for the stability of plant communities. Because A. gracilipes have invaded many tropical islands where the predominant scavengers are hermit crabs, we consider that their competitive effects are likely to be more prominent in structuring communities than predation.]