Stochasticity in a Loggerhead Turtle Population Matrix Model and Conservation Implications

Schimmel/Conrades Science Center Atrium

Loggerhead turtles are listed under the Endangered Species Act as threatened, some populations even listed as endangered. As conservation efforts work to allow this species to recover from its threatened status it is important to evaluate the effectiveness of various strategies. A stage-based population model with demographic parameters is an effective way to evaluate efforts for the loggerhead sea turtle as various efforts concentrate on different life stages. The life history of the species also means that individuals in different age classes do not have the same relative impact on populations numbers and reproduction. A mathematical model with known or estimated demographic parameters can be used to understand the impact on recovery by changing parameters of various age groups as well as to compare recovery after certain management strategies are implemented. Previous models have been deterministic however demographic stochasticity can greatly affect smaller populations like those considered threatened. I modified a stage-based population model with five distinct life stages of the loggerhead turtle. I updated demographic parameters where possible and incorporated variation in each parameter. I hope the model will help us understand the impact that variability and stochasticity can have on population projections as well as the differing impact this has on specific parameters.