Explainer: Extaille

When describing the status of a species, extant and extinct are well defined: 'existing', and 'no longer in existence', respectively. What is the appropriate term, however, for a species that is extant, but whose abundance has dropped to an exceptionally low value? In practice, we tend to describe this species as 'nearly extinct', or similar. Terms such as 'rare' and 'endangered' have multiple meanings, but none address ecological functions. Also, in conservation biology, when we ask 'what drove a species extinct?', we do not mean 'what killed the last individual?' - we mean 'what drove a species' population size so low that extinction was likely?'. There is no term for this, so we rely on imprecise wording and assume that the reader knows what we mean. Banks proposed the term 'extaille' to fill this void (pronounced ex-tayl). Extaille is the status of a species whose abundance has been reduced so much that it no longer functions as a significant part of its normal ecosystem; "extation" refers to the condition of becoming extaille. These terms have not caught on in the scientific literature, and I recommend against them. Use of this jargon could hurt communication outside the discipline, and a term like "functionally extinct" (or similar) better meets our needs.