Viability Modeling for Decision Support with Limited Data: a Lizard Case Study

Plateau Spot-tailed Earless Lizards Holbrookia lacerata are a species of ground lizard in central Texas that are under review for listing as endangered under the U.S. Endangered Species Act, but heretofore no predictive models of population dynamics or viability have been developed. We used limited available data and published demographic rates in a population viability analysis model to predict the future status of these lizards under parametric and ecological uncertainty and temporal variability. Even in cases where data are sparse and life history information are limited, viability models can help clarify the consequences of management choices given the uncertainty. Our model predicted that on average populations will decline in the future. Quasi-extinction probability was low 20 years into the future but up to 0.60 by 50 years. Extinction risk was highly dependent on the road mortality effect and the proportion of the population exposed to roadways, both of which are currently uncertain quantities. Despite these unknowns, our model enables managers to consider the future abundance and extinction risk for the species and make decisions about management to project population viability and also identifies key uncertainties for future research and monitoring.