Designing nature reserves in the face of uncertainty

Abstract

Conservation reserves are one of the most important tools for managing biodiversity. Ever since Diamond, based on theory of island biogeography, proposed that a single large reserve was preferable to several small reserves of the same total area, there has been an enduring debate about the veracity of his assertion. The so-called SLOSS debate - should we have a Single Large reserve Or Several Small reserves - features in every conservation text book and is central to conservation theory. Population dynamic models suggest that the design that minimizes the risk of extinction of species is case-specific, with the optimal number of reserves ranging between one and very many. Uncertainty is pervasive in ecology, but, the previous analyses of the SLOSS debate have not considered how uncertainty in the model of extinction risk might influence the optimal design. Here we show that when uncertainty is considered, the SLOSS problem is simplified and driven more by the aspirations of the manager than the population dynamics of the species. For a given budget of land area to be reserved in a region, the optimal solution is to have on the order of twenty or fewer reserves for any species. This result shows counter-intuitively that considering uncertainty actually simplifies rather than complicates decisions about designing nature reserves.