DOI:10.1093/sysbio/syr030 Point of View Determining Species Boundaries in a World Full of Rarity: Singletons, Species Delimitation Methods

Singletons—species only known from a single specimen—and uniques—species that have only been collected once—are very common in biodiversity sam-ples. Recent reviews suggest that in tropical arthropod samples, 30 % of all species are represented by only one specimen (Bickel 1999; Novotny and Basset 2000; Coddington et al. 2009), with additional sampling help-ing little with eliminating rarity. Usually, such sampling only converts some of the singleton species to double-tons, with new singleton species being discovered in the process (Scharff et al. 2003; Coddington et al. 2009). Here, we first demonstrate that rare species are simi-larly common in specimen samples used for taxonomic research before we argue that the phenomenon of rarity has been insufficiently considered by the new quantita