Breeding-site characteristics of pond-breeding amphibians at Whitehorse Ponds, Crater Lake National Park

Bergmann, Stefan

In the face of apparent amphibian population declines at global and regional scales, knowledge of the distribution and population dynamics of amphibian is becoming increasingly important. For pond-breeding amphibians, which require lentic habitats for egg-laying and for larval development, species patterns and population dynamics may be associated with the distribution and character of breeding sites. The purpose of this research was to examine the characteristics of pond-breeding sites for amphibians within a small and apparently undisturbed watershed, Whitehorse Ponds, in the Oregon Cascade Range. Predictions of species-patterns were based upon factors that may contribute to pond-insularity as suggested by island biogeography theory. Specifically, I examined associations between the species richness and relative abundance of breeding amphibians and the areal extent (site size), temporal extent (duration that water persists), habitat complexity (vegetation, substrate, water depth), and distribution of pond sites. Data collection for each site involved physical habitat characterization and amphibian sampling, which was comprised of basic pond (i.e., dip-netting) and funnel trapping surveys. Pond-breeding amphibians in their larval stages were detected in 7 (64%) of 11 sites. Species richness (1 salamander, 3 anurans) varied between 0 and 4 with method and site. Logistic regression revealed a significant association between water persistence and the number of larval species detected by netting, trapping, and incidental observations. There was a significant association between water persistence and the abundance of the salamander species (Ambystoma spp.) detected by trapping, but no association was found with netting. There were also significant associations between pond surface area and depth and between pond substrate class and sub-dominant substrate. The basic pond and funnel trapping surveys may detect different species, and it appears testing the effectiveness of the methods for inventory-level (e.g., species richness) and more intensive surveys (e.g., relative abundance) would be useful. The study suggests that insularity for breeding amphibians may occur at local and landscape scales. A metapopulation approach that balances local and landscape characters may be most appropriate in pursuing the notion of pond insularity and breeding amphibians.

Breeding-site characteristics of pond-breeding amphibians at Whitehorse Ponds, Crater Lake National Park

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