Demographics of an ornate box turtle population experiencing minimal human-induced disturbances
Human-induced disturbances may threaten the viability of many turtle populations, including populations of North American box turtles. Evaluation of the potential impacts of these disturbances can be aided by long-term studies of populations subject to minimal human activity. In such a population of ornate box turtles (Terrapene ornata ornata) in western Nebraska, we examined survival rates and population growth rates from 1981–2000 based on mark–recapture data. The average annual apparent survival rate of adult males was 0.883 ( se = 0.021) and of adult females was 0.932 ( se = 0.014). Minimum winter temperature was the best of five climate variables as a predictor of adult survival. Survival rates were highest in years with low minimum winter temperatures, suggesting that global warming may result in declining survival. We estimated an average adult population growth rate ( λ^ ) of 1.006 ( se = 0.065), with an estimated temporal process variance ( σ^ 2 ) of 0.029 (95% ci = 0.005–0.176). Stochastic simulations suggest that this mean and temporal process variance would result in a 58% probability of a population decrease over a 20-year period. This research provides evidence that, unless unknown density-dependent mechanisms are operating in the adult age class, significant human disturbances, such as commercial harvest or turtle mortality on roads, represent a potential risk to box turtle populations.