Evaluating the assumptions of population projection models used for conservation

Abstract

Population projection models, such as matrix and integral projection models, are used increasingly to understand potential effects of anthropogenic stressors and inform conservation actions. However, vital rate and life history information needed to create robust population models is often missing or incomplete, making assumptions about parameters and population processes necessary. Understanding how assumptions affect results is critical, particularly if the study will be used to guide policy or management actions. I review published amphibian population projection models to determine whether model output is evaluated with population data, what assumptions are made, and whether sensitivity analyses are performed. I found that only 21% of published models were evaluated with population data, and most models (67%) were explored with sensitivity analyses. I then simulated the effects of four assumptions and varying population carrying capacities on model output and sensitivity results using existing matrix population models from three amphibian species with different life histories: Anaxyrus boreas, Lithobates sylvaticus, and Ambystoma maculatum. Simulations showed that changes in model output and sensitivity analyses under different assumptions depended more on the species examined than the assumption implemented. There were changes in which parameters model output was most sensitive to under all assumptions examined for all species, suggesting caution when using results if there is great uncertainty about model assumptions. Models and their parameterization should be regularly updated with new information to ensure conservation biologists are using the most robust information on potential outcomes of threats and conservation actions.