8.74 Million Species on Earth

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Census time again, but don't look for a form in the mailbox. This census estimated the number of species on Earth.

Eight million, seven hundred and four thousand eukaryote species share this planet, give or take 1.3 million. Eukaryotes have cells with nuclei and other membrane bound structures, which means bacteria and other simple organisms were excluded from the count.

But it looks like a lot of species neglected to fill out their census cards. Eighty-six percent of all land-dwelling species and 91 percent in the water have yet to be discovered and cataloged by science, according to an estimate published in PLoS Biology by the Census of Marine Life scientists.

To complete their count of life on Earth, the scientists didn't go from door to door, or crevice to cave as the case may be. They used a statistical technique to extrapolate from patterns in branches of the taxonomic classification system started 253 years ago by Carl Linnaeus.

There are 1.2 million species officially registered in the Catalogue of Life and the World Register of Marine Species. The researchers discovered numerical relationships between the higher levels of taxonomic division, like order and phylum, and the number of species. Using these patterns they were able to make a more realistic estimate of species numbers that previous guesses, which ranged from 3 to 100 million.

"We discovered that, using numbers from the higher taxonomic groups, we can predict the number of species,” said Sina Adl, one of the co-authors of the study. “The approach accurately predicted the number of species in several well-studied groups such as mammals, fishes and birds, providing confidence in the method."

Census Results for the Five Kingdoms of Eukaryotes (approximate)

  • ANIMALS – 7.77 million species (of which 953,434 have been described and cataloged)
  • PLANTS – 298,000 species (of which 215,644 have been described and cataloged)
  • FUNGI – 611,000 species (of which 43,271 have been described and cataloged)
  • PROTOZOA – 36,400 species (single-cell organisms with animal-like behavior, such as movement, of which 8,118 have been described and cataloged)
  • CHROMISTS – 27,500 species (including, brown algae, diatoms, water molds, of which 13,033 have been described and cataloged)

Many of the researchers involved in the census look forward to the discovery of the millions of species yet to be described, but they fear that many species may disappear before they are even discovered.

BLOG: Lack of Spare Species Leaves Ecosystems Flat

"We have only begun to uncover the tremendous variety of life around us," says co-author Alastair Simpson. "The richest environments for prospecting new species are thought to be coral reefs, seafloor mud and moist tropical soils. But smaller life forms are not well known anywhere. Some unknown species are living in our own backyards — literally."

"The question of how many species exist has intrigued scientists for centuries and the answer, coupled with research by others into species' distribution and abundance, is particularly important now because a host of human activities and influences are accelerating the rate of extinctions,” said lead author Camilo Mora of University of Hawaii and Dalhousie University in Halifax, Canada.

BLOG: Animal, Plant Species Less Diverse Than Once Thought

“Many species may vanish before we even know of their existence, of their unique niche and function in ecosystems, and of their potential contribution to improved human well-being,” said Mora.

"Awaiting our discovery are a half million fungi and moulds whose relatives gave humanity bread and cheese," says Jesse Ausubel, Vice-President of the Alfred P. Sloan Foundation and co-founder of the Census of Marine Life.

Another author, Boris Worm, noted that the International Union for the Conservation of Nature has assessed only 59,508 species, of which 19,625 are classified as threatened. That means less than 1% of life on Earth is being watched for threats of extinction.

BLOG: Global Biodiversity Still in Peril, Despite Progress

Just as every man's death diminished John Donne, every species' extinction diminishes humanity as well. For example, humans depend of wild types of plants to improve the hardiness and productivity of our crops.

Robert May, Lord of Oxford, published a commentary along with the census in which he said, "(W)e increasingly recognize that such knowledge is important for full understanding of the ecological and evolutionary processes which created, and which are struggling to maintain, the diverse biological riches we are heir to.”

“Such biodiversity is much more than beauty and wonder, important though that is. It also underpins ecosystem services that — although not counted in conventional GDP — humanity is dependent upon," May said.

He noted that in the 1970's a strain of rice created by crossing conventional crop species with one from the wild resulted in a 30 percent increase in grain yield.

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"Given the looming problems of feeding a still-growing world population, the potential benefits of ramping up such exploration are clear," May said.

Completing that exploration May calls for may be a long way off. The study estimated that describing all remaining species using traditional approaches could require up to 1,200 years of work by more than 300,000 taxonomists.

The study even managed to put a price tag on describing all the species on Earth, $364 billion.

"With the clock of extinction now ticking faster for many species, I believe speeding the inventory of Earth's species merits high scientific and societal priority. Renewed interest in further exploration and taxonomy could allow us to fully answer this most basic question: What lives on Earth?" concluded Mora.

IMAGE 1:Histiophryne psychedelica is a highly atypical frogfish (Antennaridae) first described in 2009 from a handful of specimens photographed in Ambon, Indonesia in 2008. It has a vestigial, non-functional lure (illicium/esca) and probably traps its prey inside coral holes and crevices or within coral rubble. The unusual pattern is thought to mimic the appearance of several kinds of hermatypic coral, and while varying slightly from individual to individual, appears to remain unchanged throughout the life of each individual. (Photo by: David Hall)

IMAGE 2: Carolus Linnaeus in Laponian costume; replica of a painting in Estate Hartenkamp by

Hendrik Hollander (1823-1884) (Wikimedia Commons)

IMAGE 3: A coral reef in Timor (Wikimedia Commons)