Quantitative tools for implementing the new definition of significant portion of the range in the Endangered Species Act
In July 2014, the U.S. Fish and Wildlife Service and National Marine Fisheries Service announced a new policy interpretation for the Endangered Species Act. According to the Act, a species must be listed as threatened or endangered if it is determined to be threatened or endangered in a significant portion of its range. The 1973 law does not define “significant portion of its range,” leading to concerns that interpretations of “significant” by federal agencies and the courts could be inconsistent. The 2014 policy seeks to provide consistency by establishing that a portion of the range should be considered significant if the associated individuals’ “removal would cause the entire species to become endangered or threatened.” Here, we review quantitative techniques to assess whether a portion of a species’ range is significant according to the new guidance. Our assessments are based on the “3R” criteria – Redundancy (i.e., buffering from catastrophe), Resiliency (i.e., ability to withstand stochasticity), and Representation (i.e., ability to evolve) – that the Fish and Wildlife Service uses to determine if a species merits listing. We identify data needs for each quantitative technique and indicate which methods might be implemented given the data limitations typical of rare species. We also identify proxies that may be used with limited data. To assess potential data availability, we evaluate seven example species by assessing the data in their Species Status Assessments, which document all the information used during a listing decision. Our evaluation suggests that resiliency assessments will likely be most constrained by limited data. While we reviewed quantitative techniques for the US Endangered Species Act, other countries have legislation requiring identification of significant areas that could benefit from this research.