Estimating Viability of Gopher Tortoise Populations

摘要

Although the gopher tortoise (Gopherus polyphemus) is widespread across the southeastern United States where conditions are favorable, the species is in serious decline. While biologists and land managers might consider any of a variety of in-situ and ex-situ management options when determining how best to manage individual populations, there are no good decision tools for evaluating or predicting whether the existing population is viable in the long term. This study developed demographic models for gopher tortoise populations and has proposed to use those models to predict outcomes for a variety of population conditions and management scenarios. The major limiting factor in the development of models was the availability of complete lifehistory data. Because of its demonstrated importance in population stability in other turtle species, adult survivorship was assumed to be high in all model scenarios. However, reproduction and survivorship of other life stages varied among simulations. The model results demonstrated that, of the parameters manipulated, hatchling survivorship was the most critical life history stage because of the very small likelihood that hatchlings survive to their second year. Any management actions that increase hatchling success are likely to increase population viability significantly.