Implications of endemics-area relationships for estimates of species extinctions

Species are disappearing at unprecedented rates because of habitat destruction. Lack of detailed knowledge about total numbers of species and their global or regional distributions, however, makes it difficult to quantify extinction rates precisely. Current estimates of extinction rates attributed to habitat destruction generally rely on species-area relationships. Many of the predictions based on species-area relationships, however, appear to overestimate the extent of current species extinction. In a previous paper, we used the species-area relationship as our starting point to derive a relationship for the areal distribution of endemics within a habitat, or an "endemics-area relationship." The endemics area relationship is logically and mathematically consistent with the species-area relationship, but it provides additional information about the distribution of species within a biome. In this paper, we use the endemics-area relationship to improve estimates of species extinction rates attributed to habitat destruction or conversion. At low levels of habitat destruction, estimates of species loss using the endemics-area relationship are significantly lower than existing estimates, but a rapid rise in predicted species loss when a threshold of habitat loss is exceeded suggests that extrapolation of recent rates of species loss may underestimate future species extinctions under continued land clearing.