, Volume 160, Issue 1, pp 187–194 | Cite as

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

  • Alice McNatty
  • Kirsti L. Abbott
  • Philip J. Lester
Community Ecology - Original Paper


Invasive species can dramatically alter trophic interactions. Predation is the predominant trophic interaction generally considered to be responsible for ecological change after invasion. In contrast, how frequently competition from invasive species contributes to the decline of native species remains controversial. Here, we demonstrate how the trophic ecology of the remote atoll nation of Tokelau is changing due to competition between invasive ants (Anoplolepis gracilipes) and native terrestrial hermit crabs (Coenobita spp.) for carrion. A significant negative correlation was observed between A. gracilipes and 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 and 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 and drove 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 δ15 N 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 δ15 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.


Anoplolepis gracilipes Exclusion Carrion Invasive ants Trophic ecology 



We would like to thank the Pulenuku and Taupulega of Nukunonu Atoll, Tokelau, for permission to conduct this study and for support during fieldwork. Megan Sarty, Luka Luka and Kelemete Perez assisted with field work. Two anonymous referees and Nate Sanders provided comments that substantially improved this manuscript. This project was funded by the Royal Society of New Zealand Marsden Fund, The Pacific Conservation and Development Trust and Victoria University of Wellington.

Supplementary material

442_2009_1279_MOESM1_ESM.doc (643 kb)
Supplementary material 1 (DOC 643 kb)


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Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • Alice McNatty
    • 1
  • Kirsti L. Abbott
    • 2
  • Philip J. Lester
    • 1
  1. 1.School of Biological ScienceVictoria University of WellingtonWellingtonNew Zealand
  2. 2.Science FacultyMonash UniversityMelbourneAustralia

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