LAUSR

Extinct in the Wild (EW) species are placed at the highest risk of extinction under the International Union for Conservation of Nature Red List, but the extent and variation in this risk have never been evaluated. Harnessing global databases of ex situ animal and plant holdings, we report on the perilous state of EW species. Most EW animal species—already compromised by their small number of founders—are maintained at population sizes far below the thresholds necessary to ensure demographic security. Most EW plant species depend on live propagation by a small number of botanic gardens, with a minority secured at seed bank institutions. Both extinctions and recoveries are possible fates for EW species. We urgently call for international effort to enable the latter. Description Managing species on the brink As we face a global extinction crisis, international commitments promise to prevent extinctions of threatened species. However, some of the most threatened species are often overlooked: those that now exist only in zoos, aquaria, gardens, or seed banks, which are classified as “extinct in the wild. ” Smith et al. synthesized data on extinct-in-the-wild plant and animal species to assess their state of risk and what actions are being taken to recover them. Most ex situ populations are small (less than 1000 individuals) and were founded by few individuals, likely with low genetic diversity. Reestablishment of species in the wild has been successful in some cases, but it has only been attempted for about one-fourth of current extinct-in-the-wild species. —BEL A review explains that species extinct in the wild may recover after reintroduction if ex situ populations maintain genetic diversity. BACKGROUND As international commitments to prevent extinction and improve the status of threatened species go unmet, a crisis of species loss unprecedented in human history intensifies. The field of conservation biology has, however, begun to demonstrate that species can be recovered, and extinctions in the wild prevented and even reversed. These successes suggest that the post-2020 global biodiversity draft targets of arresting the increase in extinction rates and reducing the proportion of threatened species are within our capacity. A nexus of responsibility, vulnerability, and opportunity lies in those species that—having been entirely extirpated in the wild—exist solely in zoos, aquariums, botanical gardens, or seed banks—i.e., those that qualify for the International Union for Conservation of Nature (IUCN) Red List of Threatened Species (Red List) category of extinct in the wild (EW). This is a considerably overlooked category; despite being considered most at risk, the populations of EW species are not assessed under the Red List process. Consequently, we have largely ignored the extent of, and variation in, extinction risk of the very group of species for which humans are most responsible, and whose futures are among the least assured. ADVANCES We reveal the dynamic and perilous state occupied by EW species. We provide an overview of the fates of the 95 species that, since 1950, are known to have persisted in ex situ care despite extirpation in the wild and characterize the present statuses of the 84 species currently assessed as EW. We found considerable variation and alarming deficiencies in factors critical to their long-term recovery potential. Where known, most EW species, already compromised by their small number of founders, are maintained at levels at which the risks to demographic security and loss of genetic diversity are considered intolerably high. Further, most depend on maintenance at a small number of institutions. Even when individuals are spread across institutions, metapopulation management is often lacking, especially in plants. By pausing generational turnover, seed storage may offer protection from many ex situ processes, but we find that most EW plant species are not represented in seed storage institutions. Underscored by the finding that we have lost 11 species entirely under our care to extinction since 1950, we highlight the need to drive recovery and return EW species to the wild. We know this to be possible as we report on 12 species that have recovered wild status having once been restricted to ex situ care. Although most EW animal species have been subject to translocations back to wild conditions, most EW plant species have not. Overall, 41 extant EW species have never been subject to such actions. OUTLOOK The cases we examined chart more than 70 years of attempts to use ex situ conservation to prevent extinction and facilitate the recovery of species on the very brink, highlighting both the fragility of this space and the potential for success despite that fragility. Ensuring that the fortunes of EW species continue to bend away from extinction requires a redoubling of effort and a collective realization—in the minds of the conservation community, legislators, and the public—of their existence and plight. In response, the IUCN World Conservation Congress 2020 called for the reestablishment of EW species in the wild by 2030. We urge a forward-looking approach to rescue, revitalize, release, and reinforce populations: responsibly rescue suitable species close to extinction into ex situ care, revitalize and strengthen current ex situ populations to ensure continued viability, engage in ambitious and innovative release programs to return species to the wild, and drive recovery of released populations through continued reinforcement and management. Though we recognize that the challenges decision makers face are considerable, we argue that real opportunities to prevent extinction and return previously lost species to the wild abound and we must take them. Ex situ care on the brink of extinction. Ex situ care can save species with declining wild populations from outright extinction. However, populations extirpated to ex situ care are in a precarious state and require growth and careful management to mitigate the risks of genetic deterioration and extinction. These populations can be crucial in species’ long-term recovery through translocations back to the wild.