Invasive ants compete with and modify the trophic ecology of hermit crabs on tropical islands |
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Authors: | Alice McNatty Kirsti L Abbott Philip J Lester |
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Institution: | (1) School of Biological Science, Victoria University of Wellington, PO Box 600, Wellington, New Zealand;(2) Science Faculty, Monash University, Melbourne, VIC, Australia |
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Abstract: | 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.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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Keywords: | Anoplolepis gracilipes Exclusion Carrion Invasive ants Trophic ecology |
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