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In many regions of the world, amphibian species have inexplicably declined or disappeared, and serious malformations have been observed, particularly in the upper Midwest region of North America. Causes for the declines and malformations probably are varied and may not even be related. The seemingly sudden declines in many amphibians, however, suggests that a vigilant approach is necessary to monitor populations and to identify causes when declines or malformations are discovered.
In the United States, amphibian declines frequently have occurred in protected areas which should provide an ideal habitat against the most common causes of decline, habitat loss and changes in land use. In particular, declines in western National Parks have concerned biologists, resource managers, and legislators to the extent that Congress authorized the U.S.
Geological Survey to set up a national amphibian monitoring program on Federal lands to develop the sampling techniques and biometrical analyses necessary to determine status and trends, as well as identify possible causes of amphibian declines and malformations when they are discovered.
Great Smoky Mountains National Park is the most visited park in the National Park Service system. It is also a center of salamander diversity in North America (with 31 species recorded historically) and contains a moderate number of frog species (13 species recorded historically). Because of this diversity, the Park was selected as a prototype amphibian monitoring location, and USGS biologists conducted intensive sampling throughout all regions and habitats from 1998 to 2001. This report presents the results of this intensive sampling, beginning with an overview of the Park’s amphibians, the factors affecting their distribution, a review of important areas of biodiversity (particularly Cades Cove and the Cane Creek drainage), and a summary of amphibian life history in the southern Appalachians; it concludes with an extensive list of references for inventorying and monitoring amphibians.
As part of the project, a variety of inventory, sampling, and monitoring techniques were employed and tested. These included widescale visual encounter surveys of amphibians at terrestrial and aquatic sites, intensive monitoring of selected plots, randomly placed smallgrid plot sampling, leaf-litterbag sampling in streams, monitoring nesting females of selected species, call surveys, and monitoring specialized habitats, such as caves. Coupled with information derived from amphibian surveys on Federal lands using various other techniques (automated frog call data loggers, PVC pipes, drift fences, terrestrial and aquatic traps), an amphibian monitoring program was designed to best meet the needs of biologists and natural resource managers within the Park after taking into consideration the logistics, terrain, and life histories of the species found within the 2,071 km2 area of the Park. Each monitoring technique was described, including an example of how the technique was set up, what the results tell the observer, and limitations of the technique and the data derived from it.
Survey and monitoring projects are both time and labor intensive, and resource managers must make the best use of the resources available. For this reason, labor-intensive techniques, such as the use of drift fences with or without pitfall traps, and various types of trapping techniques which require continuous checking, are not recommended. Because only one species of frog (Cope’s Gray Treefrog, Hyla chrysoscelis) is likely to be attracted to PVC pipe (as a hideaway), PVC is not recommended, particularly when the species of frog can more easily be detected by listening for calls or by employing automated frog call data loggers (AFCDL). AFCDL are effective at detecting frogs within Great Smoky Mountains National Park, but are best employed in areas with extensive wetlands, such as ponds within Cades Cove. An extensive guide is included as an appendix to this manual with instructions on the construction and deployment of AFCDL. Coverboards are not recommended because of potential biases (in which species and age classes are observed) associated with sampling.
Extensive use of both small (10 x 10 m) and large (30 x 40 m) plots, either randomly sampled or “permanently” established, suggested that plot surveys are inefficient when compared with visual encounter (or time constraint) surveys. In addition, it is difficult to extrapolate counts obtained during plot surveys to actual amphibian abundance, despite efforts to standardize survey techniques, locations, and timing. Inasmuch as capture-recapture protocols are labor and time intensive, and that recapture rates are usually very low, capture-recapture surveys also are not recommended to park personnel.
The most consistent and effective survey technique to monitor amphibians within the Park, especially considering temporal, personnel, and logistic constraints, is to use visual encounter surveys based on repeated site visits. The use of leaf litterbags is also an effective nondestructive technique for determining the presence of secretive salamander larvae in streams. Data on presence (present/not detected), rather than abundance, is used to record a capture history for each species at each location. Thus, a data set is developed that, in practice, looks very much like the capture history of individuals in a typical capture-recapture study. By recording changes in these species’ capture histories through time, biologists can determine detection probabilities for each species. Trends can be determined by changes in the percentage of area occupied by a species and by changes in detection probabilities. URLs for free, downloadable software are included in this report.
Amphibians in the Park should be monitored in a three-tiered approach, which will depend on the amount of funding available. With minimum funding, biologists should:
As funding levels increase, the number of sites monitored could be increased and species with specific habitat requirements (Hellbenders, Cryptobranchus alleganiensis; cave species) can be included. In all cases, visual encounter (or time constraint) survey techniques are recommended.
Because disease agents were found within the Park (iridovirus and fungus in several species at Cades Cove), biosecurity protocols must be employed after sampling each wetland within this region. All nets, boots, and equipment must be cleansed using a 10 percent bleach solution, and researchers should carry materials into the field which will allow them to process dead, dying, or live amphibians. Disease protocols and instructions for handling amphibians suspected of harboring disease were developed by the USGS National Wildlife Health Center, and are reprinted in this report.
Sampling a diverse amphibian assemblage in an area as large as Great Smoky Mountains National Park, and with limited physical access, is not an easy task. Randomization of sampling sites is not strictly possible, so some form of a stratified sampling paradigm must be employed. Depending on the amphibian species or community sampled, biologists must use trails, watersheds, hydrological units, elevation, or other parameters to narrow sampling focus. Ultimately, however, rarer species or those with specialized habits could be overlooked. Species identification also is challenging, and the use of experienced survey personnel is critical for obtaining factual data. In this regard, USGS and Park biologists must establish cooperative efforts and training to ensure that the congressionally mandated amphibian surveys are performed in a statistically rigorous and biologically meaningful manner, and that amphibian populations on Federal lands are monitored to ensure their long-term survival.
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