Comparison of Traditional Counts and Distance Sampling Methods for Estimating the Abundance of Ute Ladies'-tresses ('Spiranthes diluvialis')

摘要

Annual monitoring for Ute ladies-tresses traditionally consists of complete counts by several observers of all the detected individuals in a population. We tested the efficacy of distance sampling methodology as an alternative to traditional counts. The theory allows for some objects to go undetected and for detectability to decrease with increasing distance from the transect line. Population estimates using distance sampling cluster methods were generally similar to traditional counts, and better models than the distance sampling individual method (P more than 0.05). We concluded traditional complete counts are most appropriate for small populations (less than 100) with distribution patterns that are linear (e.g., 4x100 m) or in small patches. Alternatively, distance sampling is more appropriate in evenly distributed large populations (more than 250) in homogenous blocks. In addition, distance sampling is replicable and generates a mean population estimate with 95% confidence intervals that facilitate tests for statistical significance among populations and years. Distance sampling provides a more valid and powerful estimate of population trends regardless of observer experience. We recommend establishing permanent distance sampling transects at 25-m intervals within contiguous populations of Ute ladies-tresses to facilitate evaluating population trend significance.