An Estimated 8.7 Million Animal Species Live On Earth

August 24, 2011


A new study by scientists from the Census of Marine Life has placed the number of species of animals on planet Earth to about 8.7 million, a number based on a validated analytical technique that narrows the range much more than the previous estimate of between 3 million and 100 million.

The scientists also noted that only about a quarter of all species on the planet have been discovered, and they say that many could exist in our own backyard. So far, only 1.9 million species have been discovered. Scientists say that cataloguing all the species on Earth could take more than a thousand years.

The team warned in the journal PLoS Biology that many species will become extinct before they can be identified and studied.

The study said that 86 percent of all land-dwelling species and 91 percent of those in the planet´s oceans, lakes and rivers have yet to be discovered, described and catalogued.

Lead author in the study, Camilo Mora, of the University of Hawaii and Dalhousie University in Halifax, Nova Scotia, said in a recent press release: “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. 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.”

“This work deduces the most basic number needed to describe our living biosphere,” said co-author Boris Worm of Dalhousie University. “If we did not know — even by an order of magnitude (1 million? 10 million? 100 million?) — the number of people in a nation, how would we plan for the future?”

“It is the same with biodiversity. Humanity has committed itself to saving species from extinction, but until now we have had little real idea of even how many there are,” said Worm.

Dr. Worm noted that the recently updated Red List of endangered species issued by the IUCN assessed more than 59,000 species, of which 19.625 are classified as threatened. This means the IUCN Red List monitors less than 1 percent of world species. And the IUCN is the leading study of its kind.

Although the number of species on the planet might seem an obvious figure to know, a way to calculate it with accuracy has remained elusive until now.

In a commentary also published in the PLoS Biology journal, former Royal Society president Lord Robert May said: “It is a remarkable testament to humanity’s narcissism that we know the number of books in the US Library of Congress on 1 February 2011 was 22,194,656, but cannot tell you – to within an order of magnitude – how many distinct species of plants and animals we share our world with.”

It appears that now we can do that, he noted.

“We’ve been thinking about this for several years now – we’ve had a look at a number of different approaches, and didn’t have any success,” Derek Tittensor, a research team member, told BBC News. “So this was basically our last chance, the last thing we tried, and it seems to work.”

Tittensor, who is based at the UN Environment Program´s World Conservation Monitoring Center and Microsoft Research in Cambridge, UK, worked on the project along with his peers from Dalhousie University and the University of Hawaii.

The vast majority of the 8.7 species on the planet are animals, with progressively smaller numbers of fungi, plants, protozoa and chromists. The figure doesn´t account for bacteria and other micro-organisms.

The method the team used to come up with a plausibly accurate estimate was to look at the relationship between species and the broader groupings to which they belong.

Groups of closely related species belong to the same genus, which in turn are clustered into families, then orders, classes, phylum, and then finally into kingdoms — such as the animal kingdom.

The higher up the tree of life you look, the rarer new discoveries become. This is not surprising, as a discovery of a new species will be much more common than the discovery of a totally new phylum or class.

The team of researchers quantified the relationship between the discovery of new species and the discovery of new higher groups such as phyla and orders, and then used it to predict how many species there are likely to be.

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

The estimate came out to be 8.7 million — plus or minus a million.

The rate of new discoveries has remained about even ever since the Art Forms of Nature was compiled nearly a century ago.

“The rest are primarily going to be smaller organisms, and a large proportion of them will be dwelling in places that are hard to reach or hard to sample, like the deep oceans,” added Tittensor.

“When we think of species we tend to think of mammals or birds, which are pretty well known,” he told BBC News. “But when you go to a tropical rainforest, it’s easy to find new insects, and when you go to the deep sea and pull up a trawl, 90% of what you get can be undiscovered species.”

The scientists say they do not expect their calculations to effectively end the line of inquiry, and are looking to peers to refine methods and conclusions to come up with an even more accurate estimate of the world´s number of species.

One researcher who has looked through the paper is Professor Jonathan Baillie, director of conservation programs at the Zoological Society of London.

“I think it’s definitely a creative and innovative approach, but like every other method there are potential biases and I think it’s probably a conservative figure,” he told BBC News reporter Richard Black. “But it’s such a high figure that it wouldn’t really matter if it’s out by one or two million either way.”

“It is really picking up this point that we know very little about the species with which we share the planet; and we are converting the Earth’s natural landscapes so quickly, with total ignorance of our impact on the life in them,” said Baillie.

“We are really fairly ignorant of the complexity and colorfulness of this amazing planet,” added Worm. “We need to expose more people to those wonders. It really makes you feel differently about this place we inhabit.”

Harvard biologist Edward O. Wilson, who was not part of the study, said that many of these undiscovered species may have potential benefits, some of which could provide important medicines needed to cure and prevent disease.

“We won’t know the benefits to humanity (from these species), which potentially are enormous,” noted Pulitzer Prize-winning Wilson. “If we’re going to advance medical science, we need to know what’s in the environment.”


Mora, Worm and their colleagues predict the number of species that may exist on Earth:

–7.77 million species of animals (of which 953,434 have been described)

–298,000 species of plants (of which 215,644 have been described)

–611,000 species of fungi (of which 215,644 have been described)

–36,400 species of protozoa

–27,500 species of chromists

Based on current costs and requirements, the researchers suggest that describing all remaining species using traditional approaches could require up to 1,200 years of work by more than 300,000 taxonomists at an approximate cost of $364 billion. Fortunately, new techniques such as DNA barcoding are radically reducing the cost and time involved in identifying new species.

“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,” noted Mora. “Renewed interest in further exploration and taxonomy could allow us to fully answer this most basic question: What lives on Earth?”

Image Caption: Kiwa hirsuta, also dubbed the “yeti crab” for its silky blond setae that resembles fur, was one of some 6000 new species discovered by Census of Marine Life scientists. This interesting looking crustacean was discovered in 2005 in the South Pacific. Credit: A. Fifis/IFREMER.

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Source: RedOrbit Staff & Wire Reports

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