How Many Species, Revisited

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Science  03 Aug 2001:
Vol. 293, Issue 5531, pp. 763
DOI: 10.1126/science.293.5531.763b

Despite three centuries of avid collecting, cataloguing, and classifying, large uncertainties have surrounded the total number of species of eukaryotic organisms on Earth. Recent estimates have ranged from as few as 3 million to over 30 million. Increasingly, estimates are homing in on values at the lower end of the spectrum. Most efforts consider insects, which constitute the vast majority of terrestrial metazoa.

Dolphin and Quicke focus on the parasitic wasp family Braconidae and use two models to extrapolate from the number of described species to the total. Their first method uses the rate of taxonomic description of new species, and the second uses biogeographic comparisons with other insect groups that are better described (such as butterflies). Both estimates produce similar results, indicating that the total number of species is likely to be 2.1 to 3.4 times the number of species so far described. Extended to insects as a whole, this would place an upper bound of around 3.4 million species. — AMS

Biol. J. Linn. Soc.73, 279 (2001).

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