Fitzgerald, D., M. Freeman, K. Maloney, J.Young, A. Rosenberger, D. Kazyak, and D. Smith. Accepted with Revisions. Multispecies approaches to status assessments in support of Endangered Species classifications. Conservation Science and Practice DOI:10.111/csp2.12825.
Multispecies risk assessments have developed within many conservation policies, reflecting a widespread need for efficiency in status assessments. While some frameworks adopt procedures for assigning threatened status to ecological communities or ecosystems, multispecies assessments under the United States Endangered Species Act ultimately lead to species-level listing decisions. This presents a range of potential benefits and consequences, and guidance is needed for how multispecies approaches can be incorporated into ESA risk assessments. To aid development of such guidance, this study reviewed multispecies assessments conducted between 1993–2019 in support of ESA listing decisions to identify the ecological basis for combining species, the assessment approach used, and the policy factors that may influence their efficacy. Forty-two unique cases were identified, covering 359 individual species. Most assessments (81%) included between 2–5 species, although some contained as many as 82. A common theme among reviewed cases was grouping narrow endemics or habitat specialists based on taxonomic relatedness, similar distributions, and common threats to persistence, although what constituted similar distributions varied from zero to nearly 100% overlap in ranges. All assessments included a combined threats analysis, but relatively few employed a similar species’ response model or expert elicitation process. While ESA risk assessments are distinct from policy decisions, majority of assessments resulted in decisions that all species warranted endangered status. The challenge with developing guidance for selecting species based on qualitative proxies such as common geographies or threats is that ecological patterns and processes are scale dependent. We therefore argue for a tiered approach that recognizes these assessments as a collection of methods with varying degrees of potential bias and gains in efficiency. The ESA presents several unique challenges for implementing multispecies risk assessments, but a flexible approach may provide opportunities to realize increased efficiency while minimizing the risk of biasing decisions.