Camilo Mora; Derek P. Tittensor; Sina Adl; Alastair G. B. Simpson; Boris Worm

“ Assessment of this pattern for all kingdoms of life on Earth predicts ∼8.7 million (±1.3 million SE) species globally, of which ∼2.2 million (±0.18 million SE) are marine. Our results suggest that some 86% of the species on Earth, and 91% in the ocean, still await description. Closing this knowledge gap will require a renewed interest in exploration and taxonomy, and a continuing effort to catalogue existing biodiversity data in publicly available databases. ”

“ The contrasting patterns in the description of new species and new higher taxa suggest that taxonomic effort is probably not driving observed flattening of accumulation curves in higher taxonomic levels as there is at least sufficient effort to maintain a constant description of new species. ”

“ With extinction rates now exceeding natural background rates by a factor of 100 to 1,000 [30] , our results also suggest that this slow advance in the description of species will lead to species becoming extinct before we know they even existed. High rates of biodiversity loss provide an urgent incentive to increase our knowledge of Earth's remaining species. ”

“ This underestimation in the number of higher taxa would lower our prediction of the number of species through our higher taxon approach, which suggests that our species estimates are conservative, particularly for poorly sampled taxa. ”

“ When applied to all eukaryote kingdoms, our approach predicted ∼7.77 million species of animals, ∼298,000 species of plants, ∼611,000 species of fungi, ∼36,400 species of protozoa, and ∼27,500 species of chromists; in total the approach predicted that ∼8.74 million species of eukaryotes exist on Earth (Table 2) . Restricting this approach to marine taxa resulted in a prediction of 2.21 million eukaryote species in the world's oceans (Table 2) . We also applied the approach to prokaryotes ”

“ Vertical lines indicate the consensus standard error. (P–T) Frequency distribution of the number of subordinate taxa at different taxonomic levels. For display purposes we present only the data for Animalia; lines and test statistics are from a regression model fitted with a power function. Changes in taxonomic effort
Taxonomic effort can be a strong determinant of species discovery rates [14] . Hence the estimated asymptotes from the temporal accumulation curves of higher taxa (dotted horizontal line in Figure 1A–1E) might be driven by a decline in taxonomic effort. ”

“ To account for yet-to-be-discovered higher taxa, our approach fitted asymptotic regression models to the temporal accumulation curve of higher taxa. A critical question is how the completeness of such curves will affect the asymptotic prediction. To address this, we performed a sensitivity analysis in which the asymptotic number of taxa was calculated for accumulation curves with different levels of completeness. ”

“ Finally, we are indebted to Stuart Pimm, Andrew Solow, and Catherine Muir for helpful and constructive comments on the manuscript and to Philippe Bouchet, Frederick Grassle, and Terry Erwin for valuable discussion.The authors have declared that no competing interests exist.Funding was provided by the Sloan Foundation through the Census of Marine Life Program, Future of Marine Animal Populations project. ”