A new paper “When should we save the most endangered species?” by Howard B. Wilson et al. looks at the question of whether to concentrate funds on the most endangered species, or rather on those species that can more easily be raised to a better status, which allows targeting more, alas not so endangered species. Similar to a previous study by Martin Drechsler and me (The time horizon and its role in multiple species conservation planning), Wilson et al. find that the answer to this question depends on the time horizon of the conservation planner: for a short time horizon, targeting the most endangered species will often be optimal. If one aims at preserving biodiversity on longer timescales, however, cruel mathematics do tell that it is often more sensible support species that are less endangered first, because here the “return” on conservation funds is typically greater on the long run than for the most endangered species.
Wilson et al. presumed in their analysis that the general conservation objective is to save as many species as possible. This is sensible, but one could look at other options, too. For example, if the sole goal of a planner were to save all species (“all or nothing”), then the time horizon has no influence on the conservation decision. We discuss this in the 2008 paper. However, the “all or nothing” objective is not one that we would advice due to its tendency to use large amounts of funds on species for which the probability of survival is very low. As we show in the same paper, objectives that only put value on saving ALL species distribute funds in some situations such that the expected number of surviving species is actually MINIMIZED, which is clearly not the intend of a typical conservation planner.