Priorities for a coordinated effort on behalf of lost species: a commentary on Martin et al. (2022)

Martin et al. (2022) contributed a thoughtful quantitative analysis to the understudied conservation topic of lost species. Knowing the numbers of animals, fungi, and plants that are currently lost rather than extinct is crucial for deciding on which species to focus conservation efforts to prevent possible extinctions. To reduce this Latimerian shortfall of knowledge (i.e., number of species not known with certainty to be extant or extinct), field surveys must be employed based on a curated list of lost species with well-defined and accurately populated criteria. As the extinction crisis deepens and the conservation status of a growing number of species becomes unknown, a new area of conservation research is emerging around lost species. In parallel to Martin et al. (2022), a global standard for lost species nomenclature was also published to align and simplify terminology (Long & Rodr ıguez, 2022). This nomenclature follows a pathway of loss, from missing to lost to long-lost. A lost species is thus considered “one not confirmed alive by photographic, audio or genetic information for over 10 years in the wild and has no ex-situ population under human care. ” Missing species are those not seen in the wild and not under human care for over five years but under 10 years, while long-lost applies to those not seen in over 50 years. The lost species definition used by Martin et al. (2022) was therefore inconsistent with this proposed standard as they use over 50 years as their definition of a lost species. The focus on species lost for over 50 years (i.e., long-lost species) permits a useful comparison between long-lost and Critically Endangered (Presumed Extinct) species as per the IUCN Red List guidelines (IUCN, 2012). The result that lost species outnumber extinct species for all Classes except birds (Martin et al., 2022) demonstrates that where adequate search effort and data are available, informed decision making on the likelihood of extinction can be determined. However, in cases where severe immediate threats are the potential driver of population decline (such as disease, acute pollution, catastrophic weather, and habitat destruction) the over-50-year threshold may fail to detect the need for expedited intervention. For example, Harlequin toads (Atelopus spp.) have been devastated by the Batrachochytrium dendrobatidis fungus, leading to 70% of the species being considered Critically Endangered or Possibly Extinct in fewer than 20 years (Jaynes et al., 2022). This highlights the need for an understanding of the reason why a species has become lost. There are potentially multiple, non-exclusive explanations why a species has not been seen, such as inaccessible habitat, lack of search effort, taxonomic changes, the species is highly cryptic, and extinction. Each of these lead to different conservation actions including, but not limited to, doing nothing further, conducting searches, implementing conservation interventions, and proposing an extinction declaration. Documented classification of the driver(s) of a species’ lost status is important for determining the required action. Martin et al. (2022) stressed the critical importance, but inconsistent use, of the “year last seen” field in the IUCN Red List of Threatened Species which is the underlying knowledge base of their list. The IUCN Red List is created by thousands of volunteer experts in the IUCN Species Survival Commission (SSC) Specialist Groups, and while taxing in terms of both time and resources, the many applications and uses of the list cannot be overemphasized (Betts et al., 2019). The importance of the “year last seen” field in a Red List assessment for species not seen in over five years cannot be stressed enough, as it would permit easy identification of species in need of specific conservation attention under the banner of lost species. Making this a mandatory field in such situations would significantly support catalyzing conservation efforts for overlooked species. Martin et al. (2022) also suggested more consistent use of the Possibly Extinct marker which would help clarify expert opinion on the status of lost species. Four groups of vertebrates were collated by Martin et al. (2022) for their list of long-lost species, while Re:wild and SSC maintain a list of all lost species (lost and longlost) (Re:wild & IUCN SSC, 2022). A single, comprehensive list that includes all taxa, all stages of the pathway of loss, data on the reason(s) for loss, and proposed actions needs to be updated and published annually with a Digital Object