Estimating the number of species not yet described and their characteristics: the case of Western Palaearctic dung beetle species (Coleoptera, Scarabaeoidea)

To determine the degree of completion of Western Palaearctic dung beetlespecies inventory, as well as to ascertain some of the main geographical andmorphological characteristics associated with the probability of new speciesdescription, the available taxonomic and biogeographic information of the threeScarabaeoidea families that are associated with dung was analyzed. An asymptotic fit of the cumulative number of described species is used to estimatethe approximate number of species not yet described. Variation partitioning andhierarchical decomposition techniques were used to explore the influence ofbody size, geographical range size and geographical location variables on theprocess of species description. Results indicate that the inventories of WesternPalaearctic Scarabaeidae and Geotrupidae species are almost complete, but thataround 16% of Aphodiidae species have yet to be described. As the joint effectof geographical distribution and location is the main determinant of the speciesdescription rate in this family, it was predicted that new dung beetle specieswould be found in smaller areas of the southern and eastern Western Palaearcticregion. The species body size accounted for a negligible fraction in thevariation of the year of description. Both the geographical range size and thegeographical location are essential variables negatively correlated with theyear of species description, whose pure and combined effect can account for highpercentages in the year of description variation (from 41 to 56%). The locationof most of the taxonomic workforce in areas where broader-ranged generalist speciesprevail in the assemblages is the probable reason for this pattern.