Threatened species face similar types and numbers of threats as endangered species when listed under the Endangered Species Act

Abstract

AbstractWith species increasingly imperiled due to anthropogenic activities, conservation practitioners are tasked with determining conservation priorities to make the best use of limited resources. One way of setting priorities is to categorize species based on risk of extinction. The United States' Endangered Species Act (ESA) has two listing statuses into which imperiled species are placed to receive protections: threatened or endangered. Our objective was to identify differences between threatened and endangered (T&E) species beyond what is outlined in their ESA definitions. For 6 broad‐resolution threats (habitat modification, overutilization, pollution, species‐species interactions, environmental stochasticity, and demographic stochasticity), we investigated whether there is a difference in the number and types of threats which impacted T&E species at the time of their listing. We found that threatened (x̄ = 2.9, SD = 1.4) and endangered (x̄ = 3.0, SD = 1.1) species faced a similar number of threats at time of their listing. The only broad‐resolution threat that impacted endangered species more than threatened species was demographic stochasticity, with endangered species being 2.1 times (95% CI = 1.5–2.8) more likely to be impacted than threatened species. We examined demographic stochasticity by breaking it down into finer‐resolution threats to identify additional differences between T&E species. We found 4 finer‐resolution demographic stochasticity threats (few individuals in one population, few individuals in multiple populations, lack of reproduction, and genetic loss) to be strong predictors of endangered status. The similarities in the number and types of broad‐resolution threats faced by T&E species indicated that they are equally conservation reliant.