Shortcomings of shortcuts: common species cannot fully explain multiscale patterns of species richness

A number of “shortcuts” for assessing biodiversity and prioritizing conservation action have been proposed, one of which is to focus on a subset of the most common species. I critically evaluated the claim that common species better explain patterns of species richness than rare species, using bird data from the same spatial extent at two markedly different spatial resolutions and a third dataset for a larger spatial extent. I did find situations where common species convey more information about species richness patterns than rare species, such as in sequential correlations of species sets with total species richness. However, “hotspots” of species richness tended to be most associated with species occurring with intermediate frequency, rather than the most common (or most rare) species. Furthermore, differences in the degree and sequence of rarity across the three datasets meant that conclusions drawn from species in one dataset did not necessarily hold in the others. Overall, therefore, I found little evidence that common species alone could provide a satisfactory shortcut to understanding biodiversity, particularly given that rare species are often facing the greatest risk of extirpation or extinction. Drawing upon citizen scientists to aid in monitoring and ensuring that unusual or unique ecosystem types and configurations are surveyed may be invaluable in obtaining the thorough understanding of biodiversity needed for successful conservation outcomes.