Predicting the Pattern of Decline of African Primate Diversity: an Extinction Debt from Historical Deforestation

Abstract: Populations that have survived extensive habitat loss may still face extinction owing to a time lag between initial habitat loss and eventual population collapse. Using island biogeography theory, I investigated the potential existence and magnitude of such “extinction debts” among African forest primates as a result of historical deforestation. Forest primate species exhibited a classic species‐area relationship ( S = cA z ) with forest habitat across African countries. I conducted three tests based on the species‐area relationship that indicate extinction debts are likely to exist in African forest primates; in particular, several national extinctions should have already occurred solely as a result of forest loss in the last 50 years (if extinctions occurred simultaneously with habitat loss), but none of these extinctions have yet taken place. I also used the species‐area relationship to predict the number of species that make up the total debt accumulated since deforestation began in these countries. My results suggest that in most countries the debt currently consists of over 30% of the forest primate fauna, which usually constitutes between four and eight species. These figures are likely to be accurate because the same model predicts with a reasonable degree of precision (1) the severity of threat of extinction from deforestation faced by country endemics, (2) the distribution of regional community endemics threatened by deforestation, and (3) the total number of African species threatened by deforestation (according to the 1996 IUCN Red List). My findings indicate that although protected areas are an essential part of conservation, the protection of the remaining forest alone may not be enough to prevent extinctions caused by habitat loss.