Do predators control prey species abundance? An experimental test with brown treesnakes on Guam

Authors

  • Earl W. Campbell III,

    1. Ohio Cooperative Fish and Wildlife Research Unit, 1735 Neil Avenue, Columbus, Ohio 43210 USA
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    • Present address: USFWS, Pacific Islands Fish and Wildlife Office, 300 Ala Moana Boulevard, Room 3-122, P.O. Box 50088, Honolulu, Hawaii 96850 USA.

  • Amy A. Yackel Adams,

    Corresponding author
    1. U.S. Geological Survey Fort Collins Science Center, 2150 Centre Avenue, Building C, Fort Collins, Colorado 80526 USA
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  • Sarah J. Converse,

    1. U.S. Geological Survey Patuxent Wildlife Research Center, 12100 Beech Forest Road, Laurel, Maryland 20708 USA
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  • Thomas H. Fritts,

    1. U.S. Geological Survey, National Museum of Natural History, MRC 11, Washington, D.C. 20560-0001 USA
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    • Present address: 24 Madrone Flyway, Belen, New Mexico 87002 USA.

  • Gordon H. Rodda

    1. U.S. Geological Survey Fort Collins Science Center, 2150 Centre Avenue, Building C, Fort Collins, Colorado 80526 USA
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  • Corresponding Editor: J. B. Yavitt.

Abstract

The effect of predators on the abundance of prey species is a topic of ongoing debate in ecology; the effect of snake predators on their prey has been less debated, as there exists a general consensus that snakes do not negatively influence the abundance of their prey. However, this viewpoint has not been adequately tested. We quantified the effect of brown treesnake (Boiga irregularis) predation on the abundance and size of lizards on Guam by contrasting lizards in two 1-ha treatment plots of secondary forest from which snakes had been removed and excluded vs. two 1-ha control plots in which snakes were monitored but not removed or excluded. We removed resident snakes from the treatment plots with snake traps and hand capture, and snake immigration into these plots was precluded by electrified snake barriers. Lizards were sampled in all plots quarterly for a year following snake elimination in the treatment plots. Following the completion of this experiment, we used total removal sampling to census lizards on a 100-m2 subsample of each plot. Results of systematic lizard population monitoring before and after snake removal suggest that the abundance of the skink, Carlia ailanpalai, increased substantially and the abundance of two species of gekkonids, Lepidodactylus lugubris and Hemidactylus frenatus, also increased on snake-free plots. No treatment effect was observed for the skink Emoia caeruleocauda. Mean snout–vent length of all lizard species only increased following snake removal in the treatment plots. The general increase in prey density and mean size was unexpected in light of the literature consensus that snakes do not control the abundance of their prey species. Our findings show that, at least where alternate predators are lacking, snakes may indeed affect prey populations.

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