Different prey resources suggest little competition between non-native frogs and insectivorous birds despite isotopic niche overlap

Abstract

Non-native amphibians often compete with native amphibians in their introduced range, but their competitive effects on other vertebrates are less well known. The Puerto Rican coqui frog (Eleutherodactylus coqui) has colonized the island of Hawaii, and has been hypothesized to compete with insectivorous birds and bats. To address if the coqui could compete with these vertebrates, we used stable isotope analyses to compare the trophic position and isotopic niche overlap between the coqui, three insectivorous bird species, and the Hawaiian hoary bat. Coquis shared similar trophic position to Hawaii amakihi, Japanese white-eye, and red-billed leiothrix. Coquis were about 3 ‰ less enriched in δ15N than the Hawaiian hoary bat, suggesting the bats feed at a higher trophic level than coquis. Analyses of potential diet sources between coquis and each of the three bird species indicate that there was more dietary overlap between bird species than any of the birds and the coqui. Results suggest that Acari, Amphipoda, and Blattodea made up >90% of coqui diet, while Araneae made up only 2% of coqui diet, but approximately 25% of amakihi and white-eye diet. The three bird species shared similar proportions of Lepidoptera larvae, which were ~25% of their diet. Results suggest that coquis share few food resources with insectivorous birds, but occupy a similar trophic position, which could indicate weak competition. However, resource competition may not be the only way coquis impact insectivorous birds, and future research should examine whether coqui invasions are associated with changes in bird abundance.

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Acknowledgements

USDA APHIS National Wildlife Research Center provided funding. This research was supported by the Utah Agricultural Experiment Station, Utah State University, and approved as journal paper number 8900. We thank A. Wallis and A. Crusoe for assistance collecting samples in Hawaii, B. Mossman for laboratory assistance and insect identification, and H. Coad for bat sample preparation. This research was conducted under USU’s IACUC permit # 2371, USFWS permit MB37092B-0, Hawaii Protected Wildlife permit WL14-07, a DOFAW insect collection permit, and a NARS scientific research access permit. We thank P. Banko and two anonymous reviewers for useful commentary on an earlier version of this manuscript.

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Correspondence to Karen H. Beard.

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Smith, R.L., Beard, K.H. & Shiels, A.B. Different prey resources suggest little competition between non-native frogs and insectivorous birds despite isotopic niche overlap. Biol Invasions 19, 1001–1013 (2017). https://doi.org/10.1007/s10530-016-1333-9

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Keywords

  • Stable isotope analyses
  • 13C
  • 15N
  • Hawaiian Islands
  • Non-native amphibians