Abstract
The desire to know how many living beings there are on the planet has been a permanent obsession of biologists. Many inventories have been done, especially with large animals and plants, since naturalists began modern taxonomy in the 18th century. But there is the feeling that we are missing a large part of the diversity of microorganisms. How large this ignorance is, however, is a matter of debate. In PNAS, Locey and Lennon (1) provide one such estimate that, if true, will have microbiologists struggling with the task of describing this diversity for decades, maybe centuries. Fig. 1 A shows the distribution of primary producers on the planet, both on land and in the oceans. Despite the known difficulties of determining species and avoiding synonyms, we have a reasonable knowledge of where the ∼300,000 species of the main primary producers on land, the vascular plants, are (Fig. 1 B ). When we turn to the main primary producers in the oceans, however, we are at a loss to say how many species are there and how they are distributed. We are left with just the chlorophyll concentrations in Fig. 1 A , because the marine primary producers are microbes. The contrast between our knowledge of the diversity of macrobes and microbes is thus apparent; the paper by Locey and Lennon (1) tries to put together data on both to estimate the total number of microbial species on Earth. Fig. 1. ( A ) Abundance of primary producers on Earth. Tan to green colors on land show density of green vegetation as the normalized difference vegetation index. Deep blue to yellow color in the oceans show chlorophyll concentration (mg/m−3). Image courtesy of NASA Earth Observatory. ( B ) Number of vascular plant species on land, from 5,000 (red). Image courtesy of ref. … [↵][1]1To whom correspondence should be addressed. Email: cpedros{at}cnb.csic.es. [1]: #xref-corresp-1-1
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