Matrix and agent-based modeling of threats to a diamond-backed terrapin population

Abstract

Population models are important tools for evaluating human impacts and potential management approaches on declining species. However, often studies are limited by constraints of the specific modeling approach. In this study we considered the persistence of a diamond-backed terrapin (Malaclemys terrapin) population using two distinct modeling approaches. Two of the models were deterministic matrix models. Analysis of the discrete non-spatial models showed that female adult survival rate had the largest positive impact on population growth while delaying sexual maturity decreased population growth. The matrix models also demonstrated that an increase in crab traps skewed the sex ratio of the population in favor of females. The third model was a stochastic agent-based formulation that evaluated how increases in the number of crab traps and frequency of nest disturbances affected the long-term viability of diamond-backed terrapins. The spatial agent-based model revealed how terrapin mortality was highly sensitive to the proximity of traps to the primary terrapin habitat. Results from this project improve our understanding of threats to diamond-backed terrapins and can be used to guide conservation efforts.