Estimating the global species richness of an incompletely described taxon:an example using parasitoid wasps (Hymenoptera : Braconidae)

The need to estimate the magnitude of undescribed species richness arises f rom the limited resources available to the description and conservation of biodiversity, the continuous loss of diversity that we are currently experi encing, and the sheer scale of the task of accurate measurement. Several es timation methods have previously been described and discussed in some detai l, but the reliability of these methods is difficult to assess. In this stu dy, we use two independent methods to predict the glob al species richness of the subfamilies of the parasitic wasp family Braconidae. The first is to extrapolate from the decreasing rate of species descriptions to the point at which this rate reaches zero. The second method uses the geographical di stribution of species in two well-studied taxa (butterflies and mammals) to extrapolate from our knowledge of braconid diversity in the Palaearctic. F or the subfamilies which currently contain at least 50 species, there is a significant correlation between the proportions of undescribed species pred icted by each method. Each method predicts an average increase of between 1 00% and 200% for the Braconidae as a whole. Applying the figures we obtain to the class Insecta yields an estimate of 2.05-3.4 million global insect; species. (C) 2001 The Linnean Society of London.