A POWER ANALYSIS FOR THE USE OF COUNTS OF EGG MASSES TO MONITOR WOOD FROG (LITHOBATES SYLVATICUS) POPULATIONS

作者：Scherer Rick D^*; Tracey Jeff A

来源：Herpetological Conservation and Biology, 2011, 6(1): 81-90.

• amphibians
• Lithobates sylvaticus
• monitoring
• power analysis
• Wood Frog

Counts of numbers of egg masses have been proposed as a state variable for monitoring Wood Frog (Lithobates sylvaticus) populations, and some important benefits of this approach have been identified (e.g., low cost). If the power to detect trends in time series of numbers of egg masses is low, however, this approach may not be useful. We used computer simulation to evaluate the effects of several parameters on the statistical power of detecting trends in counts of numbers of egg masses. Results of the simulations indicate that a minimum of nine years of monitoring is necessary to have high statistical power (>= 0.80) for detecting a 10% decline per year. For populations experiencing low rates of annual decline (<= 4% annually), two decades or more of monitoring data are required to achieve high levels of power. Increasing the proportion of egg masses detected by surveyors results in only minor improvements in statistical power, while increasing the Type I error rate (alpha) results in greater improvements. Insufficient duration of financial and institutional support for collection of data is a common cause of failure in monitoring programs. The results of this study provide guidance regarding the necessary duration of monitoring programs for amphibian populations and highlight components of the sampling design that can be altered to improve statistical power.

• 出版日期2011-4