Standardized monitoring methods for amphibians in national parks and associations in time and space between amphibian abundance and environmental stressors


Principal Investigator:

  Robin E. Jung
USGS Patuxent Wildlife Research Center
12100 Beech Forest Rd.
Laurel, MD 20708-4038
Phone: (301) 497-5875
FAX: (301) 497-5784
email: robin_jung
Sam Droege, USGS Patuxent Wildlife Research Center
John R. Sauer, USGS Patuxent Wildlife Research Cente

Parks: Big Bend National Park, Shenandoah National Park, Acadia National Park


Project Summary:

        Amphibian declines world-wide have created a need for more extensive and standardized monitoring of amphibian populations and for elucidating underlying causes of amphibian declines. In response to concerns about amphibian populations, a study evaluating and validating amphibian survey techniques was initiated in Shenandoah and Big Bend National Parks under the auspices of PRIMENet.

        The goals for the project are to document spatial and temporal variation in amphibian populations and associations between amphibian populations and natural and anthropogenic environmental factors in the Parks. We will (1) evaluate bias, precision, and efficiency for several sampling methods for amphibians, (2) conduct validation studies to determine the relationship between capture indices and adjusted population estimates using capture-recapture and other techniques, 3) evaluate temporal and spatial variation in amphibian populations in association with environmental features, and (4) implement park-wide monitoring programs that will provide baseline data on amphibian populations.

        In order to design appropriate monitoring programs, it is necessary to first develop sampling frames for the species of interest, then validate and estimate variances associated with site-specific population estimates within the sampling frames. Several different sampling frames and estimation procedures will be needed to ensure that amphibian groups are adequately sampled. In the first year, emphasis will be placed on studies designed to validate population indices and estimate variation in the indices spatially and in relationship to environmental variables. In the second year, the information from the first year will be used to develop extensive surveys based on the tested indices (or visibility-adjusted population estimates) within sampling frames based on information on habitats and on spatial variation in environmental variables. In the third year, which will be continued through a series of university contracts, further development and testing of methodological and spatial components will occur.

        Sampling frames must be developed for terrestrial salamanders, stream and streamside salamanders, and frogs and toads. For each group, habitats will be identified and preliminary strata will be developed using GIS information from the parks. Within these preliminary strata, a variety of validation studies will be conducted to assess appropriate sampling methods in the first year of the project. In the second year, the GIS-based sample frames will be used to select random samples within strata and sampling (and additional validation) conducted within the strata. Based on results from the second year, the sampling frames will be reassessed and additional sampling and validation will be conducted in the third year with the intent of better documenting associations between environmental features and amphibian populations.

        Central to the development of monitoring methods is validation of population indices. In general, only a portion of animals in a given sampling area are generally encountered, and investigators must either use the count data as an index to abundance or use estimation procedures such as capture-recapture to estimate the proportion of animals missed. Indices to abundance never provide estimates of absolute abundance unless the proportion of animals sampled (the detection rate) is estimated; differences in indices can not be used to estimate population change unless the detection rates are the same in the indices that are compared. Consequently, before indices are used in a monitoring program or any analysis of population change, it is necessary to estimate detection rates to determine their magnitudes and evaluate whether the rates change over time or space. If the indices are not consistent (i.e., the detection rates differ over time or space), estimation of detection rates must be an implicit component of the monitoring program.

        With amphibians, further complications are introduced because a single sampling method cannot be used to monitor all the species. Instead, several methods must be used, each of which samples a group of species with common life history attributes. Each of these methods must be evaluated with regard to variation in detection rates for each group of species.

        We will implement a variety of validation studies for preliminary indices to amphibian abundance. Additional studies in progress at the USGS Patuxent Wildlife Research Center and other sites will provide information that will also be used to estimate detection rates for indices used in the PRIMENet monitoring. The validation studies have three primary objectives: (1) estimation of detection rates for selected indices of amphibian abundance, (2) estimation of measurement error associated with indices, and (3) estimation of spatial and temporal variation in indices, and of relevant environmental features likely to be associated with variation in indices. Where possible, these validation studies will be placed in experimental contexts where these estimates of population size and variation can be used to test for relationships with natural and anthropogenic stressors.

        In spring/summer 1999, additional tasks of sampling amphibians along a Pb gradient in Acadia National Park will be coordinated with the K. Weathers investigation of deposition gradients.


PRIMENet amphibian publications

2001 PRIMENet Meeting Presentation: PRIMENet Amphibian Project (Robin Jung, Sam Droege, John Sauer)

2000 PRIMENet Meeting Presentations: PRIMENet Amphibian Project (Robin Jung, Sam Droege and John Sauer); PRIMENet Amphibian Project 2 (Robin Jung, Sam Droege and John Sauer)

For more information about the PRIMENet Amphibian Monitoring Program visit:


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