A review of quadrat-based sampling of rare, geographically clustered populations

Some common sampling designs are reviewed from the perspective of their app ropriateness for accurately estimating the total abundance of a rare popula tion. In addition, a small simulation study was performed in which the desi gns for three populations with varying numbers of rare elements were studie d. The simulation study provided information on the efficiency of the desig ns and the shapes of the sampling distributions of the estimators. The best design was stratified random sampling in which strata were constructed so that quadrats with rare elements were confined to a single small stratum an d that stratum was disproportionately oversampled. The estimator for this d esign had the smallest variance and a sampling distribution most similar to a normal distribution. Systematic sampling is a good second choice if an a uxiliary variable on which to stratify is not available. The estimator had reasonably small variance, which was further reduced if adaptive cluster sa mpling was added. The disadvantages are that an estimate of the variance is not available if only a single systematic sample is taken and the sampling distribution of the estimator is discontinuous and definitely not shaped l iked a bell curve.