SHENANDOAH NATIONAL PARK
BIG BEND NATIONAL PARK
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PRIMENET AMPHIBIAN PROJECT AT SHENANDOAH AND BIG BEND NATIONAL PARKS
Robin E. Jung, Samuel W. Droege, and John R. Sauer
USGS Patuxent Wildlife Research Center, Laurel, MD 20708
Photo by Christopher J. Leary
Northern red salamander (Pseudotriton ruber)
In National Parks, amphibians are (hopefully) not subjected to the same degree of habitat loss and degradation which are so prominent in unprotected areas throughout the world. Yet amphibian populations everywhere, even in National Parks, can fluctuate widely in response to climatic variation and can be affected by anthropogenic stressors such as acid rain, contaminants, and increasing ultraviolet radiation. In response to concerns about widespread amphibian declines, we initiated a study in the spring of 1998 to evaluate and validate amphibian monitoring techniques at Shenandoah and Big Bend National Parks, which represent extremes in amphibian communities and environments (temperate deciduous forest and desert). The project is funded by PRIMENet (Park Research and Intensive Monitoring of Ecosystems Network), an interagency effort of the EPA and NPS.
The goals of the project are to 1) test and validate amphibian survey methods, 2) assess relationships between amphibian distribution and abundance and environmental factors in the parks, and 3) propose standardized, long-term monitoring protocols. It is important to determine efficient amphibian sampling designs which accurately reflect the populations present and which, when implemented over the long-term, could yield information on whether changes in amphibian populations over time are associated with changes in environmental factors.
SHENANDOAH NATIONAL PARK
At Shenandoah National Park, estimates of terrestrial salamander (mostly Plethodon cinereus) population size were based on capture-recapture using area-constrained searches under natural and artificial cover objects during the day and on wet nights (Table 1). We established 30 plots at six areas representing different land use histories (Fig. 1), and marked salamanders with 3 colors of elastomer at four body locations (Fig. 2). In spring 1998, we found that the proportion of salamanders (p) detected during sampling varied significantly among plots, suggesting that the use of capture-recapture is essential for estimating population sizes (Table 2). However, the adjusted population estimates are extremely variable relative to capture indices (mean daily or total counts), and may not be the best parameter to use for relating salamander populations to environmental variables such as soil pH.
For streamside salamanders, four survey techniques were used at nine streams throughout the park (Table 3, Fig. 3). In general, the 50 x 1 m transects yielded the highest species richness (Fig. 4). Certain techniques worked better for some species than others. For example, 1 m2 quadrats always revealed the presence of and provided the highest counts of Desmognathus monticola (Fig. 5). For other species, such as Eurycea bislineata, no single survey method consistently revealed the greatest abundance. Electroshocking was not a reliable technique, and the three-pass removal technique did not yield adequate estimates of population size. We will continue capture-recapture work with streamside salamanders this year.
BIG BEND NATIONAL PARK
The frogs, toads, and spadefoots in the Chihuahuan desert of Big Bend National Park are difficult to monitor, because their breeding revolves around rains that sweep through the park from June to October. Thunder storms typically hit only a portion of the park at any one time, increasing the challenge for determining when and where to monitor amphibians. Monitoring methods evaluated at Big Bend are shown in Table 4. Over 100 springs were surveyed for amphibians in 1998 (Fig. 6). Repeated spring surveys revealed dramatic temporal variation in numbers of amphibians (Fig. 7). Next year, we will increase the numbers of springs visited and visit a subset of springs on a more intensive basis.
Texas Toad (Bufo speciosus)
Photo by Kevin E. Bonine
Four night-time canoe survey routes were run five times (Fig. 8), revealing temporal variation in amphibian numbers (Table 5). Six night driving routes (Fig. 9) showed interesting patterns of amphibian distribution throughout the park (e.g., Fig. 10) which we will relate to environmental factors such as soil type, topography, and elevation.
Variation in Counts from River Visual Surveys
Rio Grande Leopard Frog Bullfrog Mean CV Mean CV Gravel Pit-Rio Grande Village 158 0.49 0.67 1.73 Solis-Rooneyís Place 75 0.77 2 0.50 Rio Grande Village-Boquillas 118 0.46 Santa Elena-Castolon 61.33 0.07 4.33 0.26
Red-Spotted Toad, Bufo punctatus
Last Updated 1/13/2000