A Power Analysis for the Use of Counts of Egg Masses to Monitor Wood Frog (Lithobates sylvaticus ) Populations

Abstract/Summary

Counts of egg masses have been proposed as a valid state variable for monitoring Wood Frog (Rana sylvatica) populations. Here, we investigate the statistical power of egg mass counts to identify trends in egg mass abundance using computer simulation. We also calculate the expected bias in using the slope of a trend line fit to a time series of egg mass counts as an estimate of trend in abundance. The results of the simulations suggest that a minimum of eight years of monitoring is necessary to achieve high statistical power for monitoring programs that use counts of Wood Frog egg masses as a state variable. In addition, the slope of a trend line fit to a time series of egg mass counts is a biased estimate of trend in abundance. Increasing the duration of monitoring, however, minimizes the bias and improves inference regarding trend. Managers and herpetologists who plan to monitor Wood Frog populations using counts of egg masses should plan on a minimum of eight years of data collection to have high power to detect trends.