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Introduced galliforms as seed predators and dispersers in Hawaiian forests

Abstract

In altered communities, novel species’ interactions may critically impact ecosystem functioning. One key ecosystem process, seed dispersal, often requires mutualistic interactions between frugivores and fruiting plants, and functional traits, such as seed width, may affect interaction outcomes. Forests of the Hawaiian Islands have experienced high species turnover, and introduced galliforms, the largest of the extant avian frugivores, consume fruit from both native and non-native plants. We investigated the roles of two galliform species as seed dispersers and seed predators in Hawaiian forests. Using captive Kalij Pheasants (Lophura leucomelanos) and Erckel’s Francolins (Pternistis erckelii), we measured the probability of seed survival during gut passage and seed germination following gut passage. We also examined which seeds are being dispersed in forests on the islands of O’ahu and Hawai’i. We found that galliforms are major seed predators for both native and non-native plants, with less than 5% of seeds surviving gut passage for all plants tested and in both bird species. Gut passage by Kalij Pheasants significantly reduced the probability of seeds germinating, especially for the native plants. Further, larger-seeded plants were both less likely to survive gut passage and to germinate. In the wild, galliforms dispersed native and non-native seeds at similar rates. Overall, our results suggest the introduced galliforms are a double-edged sword in conservation efforts; they may help reduce the spread of non-native plants, but they also destroy the seeds of some native plants. Broadly, we show mutualism breakdown may occur following high species turnover, and that functional traits can be useful for predicting outcomes from novel species’ interactions.

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Acknowledgements

This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. 1747504. Our research was also supported by the Strategic Environmental Research and Development Program (SERDP) and the U.S. Army Corps of Engineers. JVB was supported in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (Capes)—Finance Code 001. Research at HAVO was funded by T. Pratt (United States Geological Survey) and D. Hu (National Park Service). We thank R. Tam, H. Wilson, H. Horowitz, and N. Shah for assistance with data collection. We also thank J. Hoh and other staff at Waimea Valley Botanical Gardens and Kapua Kawelo and other staff at the Army Natural Resource Program on O‘ahu (ANRPO) for site access and assistance with project logistics. This is publication #16 of the Hawai‘i VINE (Vertebrate Introductions and Novel Ecosystems) Project.

Funding

This work was supported by the United States Department of Defense SERDP (award number W912HQ-14-C-0043), the US Army Corps of Engineers—Engineer Research and Development Center (grant number W9132T-17-2-0002), and the National Science Foundation (NSF) Graduate Research Fellowship Program (award number 1747504). The authors have no relevant financial or non-financial interests to disclose. JVB received a scholarship from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (Finance Code 001).

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Correspondence to Samuel B. Case.

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The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

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Appendix

Appendix

See Tables 2, 3 and 4.

Table 2 Summary from model selection, including the top models (< 2 Δ AICc from the top model) for gut passage effects on (A) seed survival and (B) seed germination
Table 3 Summary of germination trials.
Table 4 Summary of intact seeds detected in fecal samples of Kalij Pheasants and Erckel’s Francolins, summed from all feces collected between sites on O’ahu and Hawai’i

See Fig. 5.

Fig. 5
figure 5

Histogram of maximum gut passage time per trial with both bird species pooled

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Case, S.B., Postelli, K., Drake, D.R. et al. Introduced galliforms as seed predators and dispersers in Hawaiian forests. Biol Invasions (2022). https://doi.org/10.1007/s10530-022-02830-6

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  • DOI: https://doi.org/10.1007/s10530-022-02830-6

Keywords

  • Galliformes
  • Gamebirds
  • Novel ecosystem
  • Invasional meltdown
  • Island ecology