How Many Endangered Species Remain to Be Discovered in Brazil?

How many species are likely as-yet unknown to science? Even in relatively well-known groups, there may be substantial numbers of such species. It seems likely that these unknown species will be rare and threatened with extinction. Indeed, science may not discover them before they go extinct. We address these issues for a sample of endemic flowering plants and three vertebrate groups: amphibians, birds, and mammals, all from Brazil. We predict the likely numbers of missing species from models of the declining numbers of species described per five-year interval. The raw numbers increase over time, so we must scale these by the taxonomic effort. We show that while the catalogues of birds and mammals are nearly complete, the numbers of amphibians may increase by 15% and the numbers of endemic plants by ~10 to ~50% depending on region. These percentages may still seem encouragingly low, given the complexities of studying a country as large as Brazil, with its extraordinary diversity, and with many of its regions large and still poorly explored. What is more worrying is that these numbers of as-yet unknown species are broadly the same as the percentages of species that are presently considered threatened with extinction. That is, we know only half of the species in danger of extinction – and our knowledge of even those species has mostly been acquired in the last