Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Past and present processes influencing genetic diversity and effective population size in a natural population of Atlantic sturgeon.

Abstract

Threats such as habitat loss, invasive species, and overexploitation cause species extinctions; however, stochastic processes can accelerate extinction rates as census sizes decline. Using molecular and ecological data, we explored the influence of these processes on the demography of a candidate species under the U.S. Endangered Species Act - the Atlantic sturgeon Acipenser oxyrinchus oxyrinchus. We used molecular microsatellite markers to estimate the effective population size (Ne) and effective number of breeders (Nb) and we used mark-recapture data to estimate the number of spawners (Na) for Atlantic sturgeon of the Altamaha River, Georgia. We found that estimates of Nb were 7-45% less than the estimated Na over four consecutive cohorts and that skewed sex ratios could explain the relative decrease of Nb to Na. Our estimate of contemporary Ne was 125 (95% confidence interval=75-348) and was at least an order of magnitude less than our estimate of historical Ne. To explain the large discrepancy between these estimates, we tested several alternative evolutionary scenarios that might explain the observed pattern of genetic diversity. Our results indicated that the observed genetic data were indeed best explained (i.e., 0.998 posterior probability of the data given the hypothesis) by overexploitation during the last half of the 20th century.