title: New approaches narrow global species estimates for beetles, insects, and terrestrial arthropods.
abstract: It has been suggested that we do not know within an order of magnitude the number of all species on Earth [May RM (1988) Science 241(4872):1441-1449]. Roughly 1.5 million valid species of all organisms have been named and described [Costello MJ, Wilson S, Houlding B (2012) Syst Biol 61(5):871-883]. Given Kingdom Animalia numerically dominates this list and virtually all terrestrial vertebrates have been described, the question of how many terrestrial species exist is all but reduced to one of how many arthropod species there are. With beetles alone accounting for about 40% of all described arthropod species, the truly pertinent question is how many beetle species exist. Here we present four new and independent estimates of beetle species richness, which produce a mean estimate of 1.5 million beetle species. We argue that the surprisingly narrow range (0.9-2.1 million) of these four autonomous estimates--derived from host-specificity relationships, ratios with other taxa, plant:beetle ratios, and a completely novel body-size approach--represents a major advance in honing in on the richness of this most significant taxon, and is thus of considerable importance to the debate on how many species exist. Using analogous approaches, we also produce independent estimates for all insects, mean: 5.5 million species (range 2.6-7.8 million), and for terrestrial arthropods, mean: 6.8 million species (range 5.9-7.8 million), which suggest that estimates for the world's insects and their relatives are narrowing considerably.
authors.affiliation: Environmental Futures Research Institute, Griffith School of Environment, Griffith University, Nathan, QLD 4111, Australia; nigel.stork@griffith.edu.au.
authors.forename: Nigel E
authors.initials: NE
authors.lastname: Stork
authors.affiliation: Environmental Futures Research Institute, Griffith School of Environment, Griffith University, Nathan, QLD 4111, Australia;
authors.forename: James
authors.initials: J
authors.lastname: McBroom
authors.affiliation: Agronomy, Forestry, Water and Environmental Science and Technology Institute, University of Lorraine, F-54052 Nancy, France;
authors.forename: Claire
authors.initials: C
authors.lastname: Gely
authors.affiliation: Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Dookie Campus, Currawa, VIC 3647, Australia; Office of the Deputy Vice-Chancellor (Research and Innovation), Federation University Australia, Mt Helen Campus, Ballarat, VIC 3353, Australia.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Hamilton
mesh_terms: D000818:Animals; D001181:Arthropods / Q000145:classification*; D044822:Biodiversity; D049628:Body Size; D001517:Coleoptera / Q000033:anatomy & histology / Q000145:classification* / Q000235:genetics; D049810:Genetic Speciation; D007313:Insecta / Q000145:classification*
keywords: Coleoptera; biodiversity; body size; species richness