Biodiversity hotspots house most undiscovered plant species

Abstract

For most organisms, the number of described species considerably underestimates how many exist. This is itself a problem and causes secondary complications given present high rates of species extinction. Known numbers of flowering plants form the basis of biodiversity "hotspots"--places where high levels of endemism and habitat loss coincide to produce high extinction rates. How different would conservation priorities be if the catalog were complete? Approximately 15% more species of flowering plant are likely still undiscovered. They are almost certainly rare, and depending on where they live, suffer high risks of extinction from habitat loss and global climate disruption. By using a model that incorporates taxonomic effort over time, regions predicted to contain large numbers of undiscovered species are already conservation priorities. Our results leave global conservation priorities more or less intact, but suggest considerably higher levels of species imperilment than previously acknowledged.

Fig. 1.

Left: The numbers of species described per 5-y interval for three selected regions increase broadly exponentially over time. Right: Corrected for the number of taxonomists involved in their description, most regions are like Mexico and Central America in showing a pronounced decrease in the rate of species described per taxonomist, leading to a modeled increase that averages 15% more species than at present. For both the region from Ecuador to Peru and the Northern Palearctic, however, there is no decrease, suggesting that considerable numbers of species are still missing from the taxonomic catalog. In both figures, plotted data start when the region has accumulated at least 40 endemic species.

Fig. 2.

Currently known patterns of flowering plant species richness as a percent of all species (Left) and patterns when corrected for species predicted to be missing from the taxonomic record (Right). They are broadly similar; differences are noted in the text. Although our results do not take area into account, we plot the results in an equal-area projection to help visualize the sometimes confusing relationship between undiscovered species and region. We excluded gray regions (Saharan Africa and the Arabian Peninsula) from the analysis as a result of low numbers of endemic species. Original TDWG regions are shown in Fig. S1. Fig. S3 shows raw estimates of numbers of missing species in each region.

Fig. 3.

Left: The number of all of taxonomists involved in species description in a given 5-y interval, the first and last named, and just the first named. Right: The last two measures plotted against the first. The very strong correlations mean that using other counts of taxonomic effort than the one we use (all taxonomists) would not seriously alter our estimates of species numbers.