A Decision-theory Approach to Cost-effective Population Supplementation for Imperiled Species

Abstract

Despite decades of managing endangered species, few have been successfully recovered. One option to reduce this gap is to use decision analysis to weigh alternative recovery actions. Using decision analysis, we evaluated tradeoffs between recovery actions to reduce extinction risk and financial cost for the imperiled Oregon spotted frog (Rana pretiosa). We simulated population supplementation via captive breeding or head-starting, and releasing offspring into the wild as larvae or young of the year. We ranked the efficacy of recovery scenarios, represented by a culmination of a series of decision points, to reduce the 10-year extinction risk below 10% while minimizing financial costs. We explored how rankings varied with respect to the extinction risk target, the endangered population size, and the reproductive output captive females. Our top-ranked pathway was to supplement with captive bred larvae, resulting in a 3% reduction in extinction risk for every $100,000 spent. In general, supplementing with captive bred larvae resulted in the biggest reduction in extinction risk per dollar invested. Additionally, we found that increasing spending does not always result in a proportional reduction in extinction risk. These results link quantitative and applied conservation by considering the biological and economic efficacy to recover endangered species.