Rarity and Conservation Planning across Geopolitical Units

Abstract

Abstract: Conservation planning is usually done within geopolitical units that tend to encompass only part of the geographic range of most species. Consequently, the relative rarity of a species within the study area considered does not necessarily reflect its relative global rarity or its conservation relevance. We investigated the implications of species' rarity in complementary reserve selection across geopolitical boundaries based on data on the distribution of birds in southern Africa. Our results demonstrate that restricted‐range species have a disproportionate effect on the number and identity of the cells selected by complementarity. The most extreme situation occurs when species whose ranges occupy single cells impose the selection of those particular sites as irreplaceable cells. Not all restricted‐range species are equally important. Some are “apparent rarities” in the study area because they are vagrants, occur very marginally to their range, or have been introduced, and these are mainly irrelevant to conservation planning in a region. Filtering rare nontarget species from the data before reserve selection results in a significant increase in the efficiency of minimum complementary sets. It is particularly recommended for taxa with high mobility, in which vagrancy is more likely. Dividing the study area into geopolitical units has a profound effect on the sites selected by complementarity. It results in loss of overall efficiency, in a tendency for selection of sites at the periphery of the units, and in some species receiving more protection at the edge of their ranges than at the center. Geopolitical coordination in conservation planning may not only result in improved overall efficiency but also a better allocation of resources that improves the long‐term robustness of reserve networks.