Inventory of the Reptiles of the War in the Pacific National Historical Park, Guam

Rodda, Gordon H.
Dean-Bradley, Kathy
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Pacific Cooperative Studies Unit, University of Hawaii at Manoa
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There are no native amphibians on Guam. Reptile species of offshore islets were reported in an earlier paper (Perry et al.1998). In February through April 2001 we intensively sampled the reptiles of the mainland portions of War in the Pacific National Historical Park (WAPA). Snake populations were sampled using a mark-recapture technique to estimate population size. Two trapping grids, each four ha, were placed in the Opop section of the Asan unit. Snakes were captured, marked, released, and recaptured for 33 days. Lizards in selected units were sampled using a total removal methodology. In our application of this technique, six 10 × 10 m patches of habitat were surrounded by a lizard-proof barrier (fence at ground level to contain terrestrial lizards and canopy separation to contain arboreal species), and all aboveground vegetation was minutely inspected for lizards as it was being removed. Three samples were collected in each of two types of habitat: grassland and tangantangan forest. These yielded the first absolute population density estimates for lizards in grassland habitat on Guam and on National Park Service land. Concurrently, we sampled the lizards of the same habitat types using adhesive trapping, a technique for estimating relative abundance that has been used extensively throughout the Pacific region. Adhesive trap samples can be compared to the densities discovered through absolute removals to assess the sampling biases of the more widely used but unvalidated relative-density technique. In addition, we conducted eleven spot adhesive-trapping samples of park units not otherwise sampled. Only common species were found. Brown Treesnakes were found at low to moderate densities (7-20/ha compared to our Guam average of 29/ha). The lizard spot samples and removals indicated that several species, although fairly dense, do not generally attain densities in the sampled areas as high as in comparable tangantangan habitat elsewhere on Guam. For example, the Pacific Blue-tailed Skink (Emoia caeruleocauda) averaged 1933/ha and the Curious Skink (Carlia fusca) averaged 1800/ha compared to the Guam average of 2400/ha and 6000/ha respectively for tangantangan forest. Overall, about half of all lizard individuals were skinks (lizards in the family Scincidae, primarily day-active terrestrial species); the remainder were geckos (lizards in the family Gekkonidae, primarily nocturnal species found usually in trees). Because this sampling yielded the first absolute density estimates for grassland habitat in Guam, these samples cannot be readily compared to other samples from Guam. Compared to the tangantangan habitat of WAPA, the total density of grassland lizards was less than half, with the gecko fraction accounting for most of the difference. All geckos averaged 467/ha in the grassland plot, significantly less than the 4500/ha average in tangantangan. In addition to quantifying the lizard fauna of the WAPA in unprecedented detail, and providing data on the impact of the Brown Treesnake on Guam lizards, the data obtained from this work will be utilized for comparisons with tropical lizard assemblages throughout the world, for detailed evaluation of the role of forest structure in the habitat requirements of lizards, and for validating other techniques which may be used for sampling lizards. Representative analyses along these lines are presented.
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Rodda GH, Dean-Bradley K. 2001. Inventory of the reptiles of the War in the Pacific National Historical Park, Guam. Honolulu (HI): Pacific Cooperative Studies Unit, University of Hawaii at Manoa. Technical Report, 169. 45 pages.
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