Consequences of individual removal on persistence of a protected population of long-lived turtles

Abstract

Box turtles Terrapene carolina are long-lived vertebrates found in many habitats throughout eastern North America. Because they routinely live >30–70 years, individuals and populations likely face periodic catastrophic effects from habitat alteration, such as hurricanes and other violent storms, flooding, and climatic perturbations such as cold or drought. We used a dataset based on a 16-year mark-recapture study of a Florida box turtle population inhabiting an isolated island to model the effects of rare and chronic removal of individuals from the population. ‘Removing’ individuals based on actual sampling records allowed us to compare the resulting effects on population structure and persistence with the known demographic characteristics of the population. For the increasing population, removal had no effect on population size over a projected 50-year time span. However, only the increasing population could sustain an annual loss of up to 56 individuals (3.8% of our initial model population) per year. Beyond this level of annual removal, the population would eventually go extinct. Both the stable and declining populations were projected to become extinct by year 50, regardless of removal intensity. Irrespective of frequency, a pre-reproductive season loss leads to a smaller population than a post-reproductive season loss. These results have implications for understanding the effect of individual removal on population persistence of declining box turtle populations.