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Our objectives in this chapter are to 1) review current information on physical stressors on amphibian population declines, 2)address the roles that changes in the physical environment could play in amphibian declines, 3) make predictions about the effects of physical stressors, and 4) determine what information is needed to evaluate the effects of physical stressors on amphibian populations.

Vernal pools are sensitive environments that provide critical habitats for many species, including amphibians. In 2005 and 2006, water samples were collected from vernal pools and adjacent flowing waters in Parks in Iowa, Washington, D.C., and Maryland, prior to and just after the local use of glyphosate. Results indicate that vernal pools and adjacent streams can be contaminated by the use of herbicides within Parks to control weeds in cropped areas or noxious or nonindigenous plants. Contamination also originates from pesticide use occurring outside Park boundaries.

Amphibians occupy a range of habitats throughout the world, but species richness is greatest in regions with moist, warm climates. The objectives of this research were to model the statistical relations of anuran and caudate species richness with mean annual climate for the conterminous U.S., and to compare the strength of these relations at national and regional levels. Model variables were calculated for county and subcounty mapping units, and included 40-year (1960-99) annual mean and mean annual climate statistics, mapping unit average elevation, mapping unit land area, and estimates of anuran and caudate species richness. Climate data were derived from more than 7,500 first-order and cooperative meteorological stations and were interpolated to the mapping units using multiple linear regression models. Anuran and caudate species richness were calculated from the U.S. Geological SurveyNULLs Amphibian Research and Monitoring Initiative (ARMI) National Atlas for Amphibian Distributions. The national multivariate linear regression (MLR) model of anuran species richness had an adjusted coefficient of determination (R2) value of https://0.64 and the national MLR model for caudate species richness had an R2 value of https://0.45. Stratifying the U.S. by coarse-resolution ecological regions provided models for anurans that ranged in R2 values from https://0.15 to https://0.78. Regional models for caudates had R2 values ranging from https://0.27 to https://0.74. In general, regional models for anurans were more strongly influenced by temperature variables, while precipitation variables had a larger influence on caudate models.

We evaluated the potential toxicity of environmental mixtures of 5 classes of pesticides using concentrations from water samples collected from 50 sites on midwestern streams. Results indicated that some samples had probable toxicity to duckweed and green algae, but few are suspected of having significant toxicity to bluegill sunfish or chorus frogs.

Vernal pools are sensitive environments that provide critical habitats for many species, including amphibians. In 2005 and 2006, water samples were collected from vernal pools and adjacent flowing waters in Parks in Iowa, Washington, D.C., and Maryland, prior to and just after the local use of glyphosate. Results indicate that vernal pools and adjacent streams can be contaminated by the use of herbicides within Parks to control weeds in cropped areas or noxious or nonindigenous plants. Contamination also originates from pesticide use occurring outside Park boundaries.

Natural history note

Appendix to monitoring manual

Beavers (Castor canadensis) are ecosystem engineers, altering hydrologic regimes, ecosystem processes, and modifying community structure. How beaver alter landscape patterns of wetlands or lentic habitat (e.g., ponds) and the distribution of obligate species remains an interesting unexamined question. A database of over 100 watersheds in southwestern Montana was used to compare the scale and pattern of lentic habitat and Columbia spotted frog (Rana luteiventris) detection between watersheds with and without signs of beaver presence.

Ambient ultraviolet-b (UV-B) radiation (280 – 320 nm) has increased at north-temperate latitudes in the last two decades. UV-B can be detrimental to amphibians, and amphibians have shown declines in some areas during this same period. We documented the distribution of amphibians and salmonids in 42 remote, subalpine and alpine ponds in Olympic National Park, Washington, USA. We inferred relative exposure of amphibian habitats to UV-B by estimating the transmission of 305 and 320-nm radiation in pond water. We found breeding Ambystoma gracile, A. macrodactylum and Rana cascadae at 33%, 31%, and 45% of the study sites, respectively. Most R. cascadae bred in fishless shallow ponds with relatively low transmission of UV-B. The relationship with UV-B exposure remained marginally significant even after the presence of fish was included in the model. At 50-cm water depth, there was a 55% reduction in incident 305-nm radiation at sites where breeding populations of R. cascadae were detected compared to other sites. We did not detect associations between UV-B transmission and A. gracile or A. macrodactylum. Our field surveys do not provide evidence for decline of R. cascadae in Olympic National Park as has been documented in Northern California, but are consistent with the hypothesis that the spatial distribution of R. cascadae breeding sites is influenced by exposure to UV-B. Substrate or pond depth could also relate to the distribution of R. cascadae in Olympic National Park.