Deriving species richness, endemism, and Threatened species patterns from incomplete distribution data in the Bioko Island, Equatorial guinea

The knowledge of the spatial patterns of species richness and, particularly, of endemic and threatened species at the scale at which management activities take place is crucial for conservation. Yet, detailed descriptions of species’ distribution areas are often lacking or incomplete, especially in the tropics. This article focuses on the African island of Bioko and uses species accumulation curves to evaluate the completeness of its biological inventory for three plant groups (ferns, monocotyledons and dicotyledons), birds and monkeys. Results showed that the current inventory is fairly complete for monkeys and birds, but only covers half of the vegetation in the island. Bioclimatic models were used to estimate the potential distribution of each species and to assemble species richness patterns for each taxa and for endemic and threatened species, revealing that montane and lowland rainforests were the richest habitats, while high altitude shrubs and subalpine meadows were the poorest ones. Predicted richness values for monsoon forests were unexpectedly low for plants and birds, probably because of insufficient sampling in these areas. Additionally, the comparison of species richness patterns with the proposed delineation of protected areas for the island shows that these will cover most hotspots of species richness, endemism and threatened species, except for dicotyledonous plants and endemic birds. The potential utility of the predicted patterns for conservation priorities and initiatives in Bioko is discussed.