Improving population size estimation for larval stream plethodontids
Perofsky, Amanda Claire
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Plethodontid salamanders are among the most abundant vertebrates of forested ecosystems in the eastern United States. Southern Appalachian streams are hotspots of diversity for semi-aquatic plethodontids. A single stream may include more than a dozen plethodontid species; however, estimates of their abundance are highly variable. Stream plethodontids are potentially important predators of first and second order streams and are likely to be important nutrient sinks. Measuring the importance of stream plethodontids requires accurate determination of their abundance. This research compares abundance estimation of four stream plethodontid species by mark-recapture across six streams at the Coweeta Hydrological Laboratory LTER site. The different categories of mark-recapture models include closed-population, open-population, and robust design models to demonstrate how different model assumptions can result in a wide range of population estimates. Our results indicate that the assumptions of the closed-population and open-population methods are violated by the occurrence of temporary emigration (i.e., the nonrandom movement of individuals into (or out of) the sampling area) and that only 5% of the total population is available for capture on the surface at a given time. We believe that Pollock’s robust design model is the most appropriate population abundance estimator for stream plethodontids because of its capacity to incorporate variation in capture probabilities and to estimate temporary emigration probabilities. This study suggests that failure to consider temporary emigration can lead to significantly low-biased estimates of population size, which in turn diminishes the actual role of stream salamanders in ecosystem processes.