Estimating vertebrate biodiversity using the tempo of taxonomy – a view from Hubbert’s peak

Reservoirs of natural resources are finite and, with increasing exploitation, production typically increases, reaches a maximum (Hubbert’s peak) and then declines. Similarly, species are the currency of biodiversity, and recognized numbers are dependent upon successful discovery. Since 1758, taxonomists have exploited a shrinking reservoir of as-yet-unnamed vertebrate taxa such that rates of species description at first rose, reached a peak and then declined. Since about 1950, increases in research funding and technological advances have fostered a renewed increase in rates of discovery that continues today. Many attempts to estimate global biodiversity are forecasts from data on past rates of description. Here we show that rates of discovery of new vertebrate taxa have been dependent upon the size (richness) of the taxonomic pool under consideration and the intensity of ‘sampling’ effected by taxonomists in their efforts to discover new forms. Because neither the current number of as-yet-to-be-described taxa nor future amounts of taxonomic efforts can be known a priori, attempts to produce an accurate estimate of total global biodiversity based on past rates of discovery are largely unconstrained.