Date of this Version
Kowalewski, L. K. 2014. Accuracy or precision: implications of sample design and methodology on abundance estimation. Master's thesis. University of Nebraska, Lincoln.
Estimation of population size by spatially replicated counts (point-count method) has been used for many large-scale animal-monitoring programs, yet its application in aquatic environments has been limited. Multiple site-specific estimates of abundance can be averaged and combined with covariate data to predict total abundance across an area of interest. Covariate data also provide an understanding of the relationship between abundance and habitat use, which is a fundamental interest of many animal-population investigations. Design of sampling scenarios for point-count population-estimate surveys can influence the accuracy and precision of the population estimate. The first objective of this study was to examine how different sampling scenarios, given interaction with environmental factors, influence accuracy and precision of population estimates derived from the point-count method. In general, across the sampling scenarios combined with environmental factors evaluated, a trade-off exists between accuracy and precision of population estimates. Sample scenarios with many sample units of small area provided estimates that were consistently closer to true abundance than sample scenarios with few sample units of large area. However, when considering precision of abundance estimates, sample scenarios with few sample units of large area provided abundance estimates with smaller widths of 95% confidence intervals than abundance estimates derived from sample scenarios with many sample units of small area. Of the environmental factors evaluated, only density of individuals influenced accuracy and precision of population estimates, in which, greater density of individuals magnified the trade-off between accuracy and precision. The second objective of this study was to evaluate the applicability of the point-count population estimation method within an aquatic environment. The point-count population estimation method generated a population estimate of largemouth bass Micropterus salmoides in a small impoundment (12 ha). Spatial modeling allowed by this method provides an advantage over other population estimation methods, although refinement of sampling technique is needed to increase precision of abundance estimates derived from the point-count method within a small impoundment. The spatial component of these models allows biologists to relate abundance and detection to habitat covariates, thus providing a link to the relationship of abundance, detection, and habitat use.
Advisor: Kevin L. Pope