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Staggering numbers of undiscovered species

Every year, 15,000 new species are added to the approximately 1.3 million species named and cataloged by scientists. And that may be just the tip of the iceberg.

Using a new method of estimating biodiversity, Marine Ecologist Camilo Mora, of the University of Hawaii at Manoa, and colleagues obtained a total of approximately 8.7 million species on the earth and in the sea. Their findings were published online on August 23 in the journal PLoS Biology.

Previous estimates by taxonomic experts put the number of species anywhere between three and one hundred million. Although the current estimate narrows the range of expected diversity, it suggests that 86percent of land species and 91percent of marine species have yet to be identified and described.

Mora and colleagues' method is based on an analysis of the number of species that fall into each level of the traditional Linnaean classification system (kingdom, phyllum, class, order, family, genus, species). The authors showed that the number of organisms in the higher classification levels followed a consistent pattern from which the number of species in a group could be estimated. This method was accurate when used to predict species richness in the most well-known groups of organisms, such as birds and mammals.

This method of estimation may not hold as accurately for lesser-studied groups, such as fungi. Mora and colleagues also make clear that their estimates only apply to eukaryotic organisms and not to bacteria and archaea.

Of the species that have been described, there is a bias towards conspicuous, larger organisms with large geographical ranges and abundances. This means that most of the species that remain to be discovered are likely to be concentrated in hotspots and less explored environments such as the deep sea and soil. Finding these cryptic organisms will require extensive exploration and classification.

For the scientists who catalog global species richness, curiosity about the biodiversity of life is one motivation for the extensive work that remains. Conservation is another: It is a race against the clock to identify the Earth's remaining species and provide a reference point for current, and future, losses of biodiversity. 

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