Invasive coqui frogs are associated with differences in mongoose and rat abundances and diets in Hawaii
With the increasing rate of species being introduced to areas outside of their native ranges, non-natives are likely to interact in ways that influence each other’s populations. The high densities of invasive coqui frogs (Eleutherodactylus coqui) in Hawaii have been hypothesized to increase non-native mongoose (Herpestes auropunctatus) and rat (Rattus spp.) abundances, and in turn increase bird nest depredation rates. We compared the relative abundances of rats and mongooses and artificial bird nest predation rates at 12 sites that had plots with similar habitat invaded and not invaded by coqui frogs across the island of Hawaii. We interpret our results considering mongoose and rat stomach analyses and camera trap data collected to monitor coqui scavengers. We found that coqui presence was associated with 30% greater mongoose abundance and 17% lower Pacific rat (R. exulans) abundance. Based on our diet analyses and scavenging data, both mongooses and rats consume coquis, but mongooses were the most important consumers of coquis, which may have contributed to their increase in coqui plots. We speculate that coquis are competing with rats for invertebrate prey due to reduced Pacific rat abundance and greater amounts of fruit in rat stomachs collected in coqui-invaded compared to uninvaded plots. We did not observe any difference in bird nest predation rates in coqui-invaded and uninvaded plots. Our results suggest that the coqui invasion may increase or decrease non-native mammal populations, and non-native amphibians may serve as both novel prey and competitors to non-native mammals.
KeywordsEleutherodactylus coqui Herpestes auropunctatus Island Rattus spp. Nest predation Scavenger Trophic interactions
We thank the USDA APHIS NWRC and the USU Ecology Center for funding; the NWRC Hilo field station and technicians, A. Grant, J.J. Cieslewics, and J. Gardner for assistance; J. Young for comments on earlier versions of this manuscript and S. Durham for statistical help. We thank C. Lepczyk for his editorial assistance and two anonymous reviewers for comments that greatly improved the manuscript. This research was supported by the Utah Agricultural Experiment Station, Utah State University, and approved as journal paper number 9102. This research was conducted under access permits from the Hawaii Division of Forestry and Wildlife, Natural Area Reserves System, State Parks Department, and Injurious Wildlife Export Permit #16-05 and was conducted in compliance with USU’s IACUC guidelines as protocols #2519 and #2753.
Conceived and designed the research: KHB and ABS. Performed the research: SAH. Analyzed the data: SAH and SRS. Wrote the paper: SAH and KHB. Helped revise the paper: all authors.
Compliance with ethical standards
Conflict of interest
The authors have declared that no competing interests exist.
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