Carl Zimmer The New York Times 23 Aug 11;
In the foothills of the Andes Mountains lives a bat the size of a raspberry. In Singapore, there’s a nematode worm that dwells only in the lungs of the changeable lizard.
The bat and the worm have something in common: They are both new to science. Each of them recently received its official scientific name: Myotis diminutus for the bat, Rhabdias singaporensis for the worm.
These are certainly not the last two species that scientists will ever discover. Each year, researchers report more than 15,000 new species, and their workload shows no sign of letting up. “Ask any taxonomist in a museum, and they’ll tell you they have hundreds of species waiting to be described,” says Camilo Mora, a marine ecologist at the University of Hawaii.
Scientists have named and cataloged 1.3 million species. How many more species there are left to discover is a question that has hovered like a cloud over the heads of taxonomists for two centuries.
“It’s astounding that we don’t know the most basic thing about life,” said Boris Worm, a marine biologist at Dalhousie University in Nova Scotia.
On Tuesday, Dr. Worm, Dr. Mora and their colleagues presented the latest estimate of how many species there are, based on a new method they have developed. They estimate there are 8.7 million species on the planet, plus or minus 1.3 million.
The new paper, published in the journal Public Library of Science Biology, is drawing strong reactions from other experts. “In my opinion this is a very important paper,” said Angela Brandt, a marine biologist at the University of Hamburg in Germany. But critics say that the method in the new paper can’t work, and that Earth’s true diversity is far greater.
In 1833, a British entomologist named John Obadiah Westwood made the earliest known estimate of global biodiversity by guessing how many insect species there are. He estimated how many species of insects lived on each plant species in England, and then extrapolated that figure across the whole planet. “If we say 400,000, we shall, perhaps, not be very wide of the truth,” he wrote.
Today, scientists know the Westwood figure is far too low. They’ve already found more than a million insect species, and their discovery rate shows no signs of slowing down.
In recent decades, scientists have looked for better ways to determine how many species are left to find. In 1988, Robert May, an evolutionary biologist at the University of Oxford, observed that the diversity of land animals increases as they get smaller. He reasoned that we probably have found most of the species of big animals, like mammals and birds, so he used their diversity to calculate the diversity of smaller animals. He ended up with an estimate 10 to 50 million species of land animals.
Other estimates have ranged from as few as 3 million to as many as 100 million. Dr. Mora and his colleagues believed that all of these estimates were flawed in one way or another. Most seriously, there was no way to validate the methods used, to be sure they were reliable.
For the new estimate, the scientists came up with a method of their own, based on how taxonomists classify species. Each species belongs to a larger group called a genus, which belongs to a larger group called a family, and so on. We humans, for example, belong to the class of mammals, along with about 5,500 other species.
In 2002, researchers at the University of Rome published a paper in which they used these higher groups to estimate the diversity of plants around Italy. At three different sites, they noted the number of genera, families and so on. There were fewer higher-level groups than lower ones at each site, like the layers of a pyramid. The scientists could estimate how many species there were at each site, much as it’s possible to estimate how big the bottom layer of a pyramid based on the rest of it.
The paper drew little notice at the time, but Dr. Mora and his colleagues seized on it, hoping to use the method to estimate all the species on Earth. They charted the discovery of new classes of animals since 1750. The total number climbed steeply for the first 150 years and then began to crest — a sign that we’re getting close to finding all the classes of animal. They found that the discovery rate of other high-level groups has also been slowing down. The scientists built a taxonomic pyramid to estimate the total number of species in well-studied groups, like mammals and birds. They consistently made good predictions.
Confident in their method, the scientists then used it on all major groups of species, coming up with estimates of 7.7 million species of animals, for example, and 298,000 species of plants. Although the land makes up 29 percent of the Earth’s surface, the scientists concluded that it is home to 86 percent of the world’s species.
“I think it is an interesting and imaginative new approach to the important question of how many species actually are alive on earth today,” said Lord May.
But Terry Erwin, an entomologist at the Smithsonian Institution, think there’s a big flaw in the study. There’s no reason to assume that the diversity in little-studied groups will follow the rules of well-studied ones. “They’re measuring human activity, not biodiversity,” he said.
David Pollock, an evolutionary biologist at the University of Colorado who studies fungi — a particularly understudied group — agrees. “This appears to be an incredibly ill-founded approach,” he said. There are 43,271 cataloged species of fungi, based on which Dr. Mora and his colleagues estimate there are 660,000 species of fungi on Earth. But other studies on fungus diversity suggest the number may be as high as 5.1 million species.
The authors of the new study acknowledge that their method doesn’t work well with bacteria. Scientists have only started to really dig into the biodiversity of microbes, and so they are finding high-level groups of bacteria at a brisk pace. Dr. Mora and his colleagues write that their estimate — about 10,000 species — should be considered a “lower bound.”
Microbiologists, on the other hand, are fairly sure the diversity of microbes will turn out to dwarf the diversity of animals. A single spoonful of soil may contain 10,000 different species of bacteria, many of which are new to science.
Jonathan Eisen, an expert on microbial diversity at the University of California, Davis, said he found the new paper disappointing.
“This is akin to saying, ‘Dinosaurs roamed the Earth more than 500 years ago,’ ” he said. “While true, what is the point of saying it?”
Number of species on Earth tagged at 8.7 million
Most precise estimate yet suggests more than 80% of species still undiscovered.
Lee Sweetlove Nature 23 Aug 11;
There are 8.7 million species on our planet — give or take 1.3 million. The latest biodiversity estimate, based on a new method of prediction, dramatically narrows the range of 'best guesses', which was previously between 3 million and 100 million. It means that a staggering 86% of land species and 91% of marine species remain undiscovered.
Camilo Mora, a marine ecologist at the University of Hawaii at Manoa, and his colleagues at Dalhousie University in Halifax, Canada, have identified a consistent scaling pattern among the different levels of the taxonomic classification system (order, genus, species and so on) that allows the total number of species to be predicted. The research is published in PLoS Biology1 today.
Mora argues that knowing how many species there are on Earth is one of the most important questions in science. "Finding this number satisfies a basic scientific curiosity," he says.
Bob May, a zoologist at the University of Oxford, UK, who wrote a commentary on the work2, agrees. "Knowing how many plants and animals there are on the planet is absolutely fundamental," he says. He also highlights the practical significance: "Without this knowledge, we cannot even begin to answer questions such as how much diversity we can lose while still maintaining the ecosystem services that humanity depends upon."
But the unstinting efforts of field taxonomists are not going to provide the number any time soon. In the more than 250 years since Swedish biologist Carl Linnaeus began the science of taxonomy, 1.2 million species have been identified and classified — less than 15% of Mora's new total. At this pace, May estimates that it will take another 480 years to complete the job of recording all species.
The catalogue of life
Instead, scientists have tried to predict the total number of species from the number already known. Some of the estimates amount to little more than educated guesses. "These predictions are unverifiable and experts change their mind," says Mora. Other approaches use assumptions that he describes as "unreliable and easy to break".
Mora's method is based on an analysis of the taxonomic classification for all 1.2 million species currently catalogued. Linnaeus's system forms a pyramid-like hierarchy — the lower the category, the more entities it contains. There are more species than genera, more genera than families, more families than orders and so on, right up to the top level, domain.
Mora and his colleagues show that a consistent numerical trend links the numbers in each category, and that this can be used to predict how many entities there should be in poorly catalogued levels, such as species, from the numbers in higher levels that are much more comprehensively described.
"The unique thing about this approach is that we are able to validate it," he says. "By testing the predictions against well catalogued groups such as mammals, birds, reptiles and amphibians, we were able to show that we could predict the correct number of species."
The analysis also reveals that some groups are much better known than others. For example, some 72% of the predicted 298,000 plant species on land have already been documented, in comparison with only 12% of predicted land animal species and 7% of predicted land fungi species.
May is impressed. "I like this approach. Not only is it imaginative and novel, but the number it comes up with is within the range of my own best estimate!"
References
Mora, C. , Tittensor, D. P. , Adl, S. , Simpson, A. G. B. & Worm, B. PLoS Biol. 9, e1001127 (2011).
May, R. M. PLoS Biol. 9, e1001130 (2011).
How many species on Earth? 8.7 million
Most precise estimate ever is based on novel, validated analytical technique; Yet to be discovered, described, catalogued: 91 percent of marine species, 86 percent of species overall
Census of Marine Life EurekAlert 23 Aug 11;
Eight million, seven hundred thousand species (give or take 1.3 million).
That is a new, estimated total number of species on Earth -- the most precise calculation ever offered -- with 6.5 million species found on land and 2.2 million (about 25 percent of the total) dwelling in the ocean depths.
Announced today by Census of Marine Life scientists, the figure is based on an innovative, validated analytical technique that dramatically narrows the range of previous estimates. Until now, the number of species on Earth was said to fall somewhere between 3 million and 100 million.
Furthermore, the study, published today by PLoS Biology, says a staggering 86% of all species on land and 91% of those in the seas have yet to be discovered, described and catalogued.
Says lead author Camilo Mora of the University of Hawaii and Dalhousie University in Halifax, Canada: "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," says 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."
Dr. Worm notes that the recently-updated Red List issued by the International Union for the Conservation of Nature assessed 59,508 species, of which 19,625 are classified as threatened. This means the IUCN Red List, the most sophisticated ongoing study of its kind, monitors less than 1% of world species.
The research is published alongside a commentary by Lord Robert May of Oxford, past-president of the UK's Royal Society, who praises the researchers' "imaginative new approach."
"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," Lord May writes.
"(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."
Drawing conclusions from 253 years of taxonomy since Linnaeus
Swedish scientist Carl Linnaeus created and published in 1758 the system still used to formally name and describe species. In the 253 years since, about 1.25 million species -- roughly 1 million on land and 250,000 in the oceans -- have been described and entered into central databases (roughly 700,000 more are thought to have been described but have yet to reach the central databases).
To now, the best approximation of Earth's species total was based on the educated guesses and opinions of experts, who variously pegged the figure in a range from 3 to 100 million -- wildly differing numbers questioned because there is no way to validate them.
Drs. Mora and Worm, together with Dalhousie colleagues Derek P. Tittensor, Sina Adl and Alastair G.B. Simpson, refined the estimated species total to 8.7 million by identifying numerical patterns within the taxonomic classification system (which groups forms of life in a pyramid-like hierarchy, ranked upwards from species to genus, family, order, class, phylum, kingdom and domain).
Analyzing the taxonomic clustering of the 1.2 million species today in the Catalogue of Life and the World Register of Marine Species, the researchers discovered reliable numerical relationships between the more complete higher taxonomic levels and the species level.
Says Dr. Adl: "We discovered that, using numbers from the higher taxonomic groups, we can predict the number of species. The approach accurately predicted the number of species in several well-studied groups such as mammals, fishes and birds, providing confidence in the method."
When applied to all five known eukaryote* kingdoms of life on Earth, the approach predicted:
~7.77 million species of animals (of which 953,434 have been described and cataloged)
~298,000 species of plants (of which 215,644 have been described and cataloged)
~611,000 species of fungi (moulds, mushrooms) (of which 43,271 have been described and cataloged)
~36,400 species of protozoa (single-cell organisms with animal-like behavior, eg. movement, of which 8,118 have been described and cataloged)
~27,500 species of chromista (including, eg. brown algae, diatoms, water moulds, of which 13,033 have been described and cataloged)
Total: 8.74 million eukaryote species on Earth.
(* Notes: Organisms in the eukaryote domain have cells containing complex structures enclosed within membranes. The study looked only at forms of life accorded, or potentially accorded, the status of "species" by scientists. Not included: certain micro-organisms and virus "types", for example, which could be highly numerous.)
Within the 8.74 million total is an estimated 2.2 million (plus or minus 180,000) marine species of all kinds, about 250,000 (11%) of which have been described and catalogued. When it formally concluded in October 2010, the Census of Marine Life offered a conservative estimate of 1 million+ species in the seas.
"Like astronomers, marine scientists are using sophisticated new tools and techniques to peer into places never seen before," says Australian Ian Poiner, Chair of the Census' Scientific Steering Committee. "During the 10-year Census, hundreds of marine explorers had the unique human experience and privilege of encountering and naming animals new to science. We may clearly enjoy the Age of Discovery for many years to come."
"The immense effort entering all known species in taxonomic databases such as the Catalogue of Life and the World Register of Marine Species makes our analysis possible," says co-author Derek Tittensor, who also works with Microsoft Research and the UN Environment Programme's World Conservation Monitoring Centre. "As these databases grow and improve, our method can be refined and updated to provide an even more precise estimate."
"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."
"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. "For species discovery, the 21st century may be a fungal century!"
Mr. Ausubel notes the enigma of why so much diversity exists, saying the answer may lie in the notions that nature fills every niche, and that rare species are poised to benefit from a change of conditions.
In his analysis, Lord May says the practical benefits of taxonomic discovery are many, citing the development in the 1970s of a new strain of rice based on a cross between conventional species and one discovered in the wild. The result: 30% more grain yield, followed by efforts ever since to protect all wild varieties of rice, "which obviously can only be done if we have the appropriate taxonomic knowledge."
"Given the looming problems of feeding a still-growing world population, the potential benefits of ramping up such exploration are clear."
Based on current costs and requirements, the study suggests 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 $US 364 billion. Fortunately, new techniques such as DNA barcoding are radically reducing the cost and time involved in new species identification.
Concludes Dr. Mora: "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?"
Species count put at 8.7 million
Richard Black BBC News 23 Aug 11;
The natural world contains about 8.7 million species, according to a new estimate described by scientists as the most accurate ever.
But the vast majority have not been identified - and cataloguing them all could take more than 1,000 years.
The number comes from studying relationships between the branches and leaves of the "family tree of life".
The team warns in the journal PLoS Biology that many species will become extinct before they can be studied.
Although the number of species on the planet might seem an obvious figure to know, a way to calculate it with confidence has been elusive.
In a commentary also carried in PLoS Biology, former Royal Society president Lord (Robert) May observes: "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."
Now, it appears, we can.
"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," one of the research team, Derek Tittensor, told BBC News.
"So this was basically our last chance, the last thing we tried, and it seems to work."
Dr Tittensor, who is based at the UN Environment Programme's World Conservation Monitoring Centre (Unep-WCMC) and Microsoft Research in Cambridge, UK, worked on the project alongside peers from Dalhousie University in Canada and the University of Hawaii.
The vast majority of the 8.7 million are animals, with progressively smaller numbers of fungi, plants, protozoa (a group of single-celled organisms) and chromists (algae and other micro-organisms).
The figure excludes bacteria and some other types of micro-organism.
Linnaean steps
About 1.2 million species have been formally described, the vast majority from the land rather than the oceans.
The trick this team used was to look at the relationship between species and the broader groupings to which they belong.
In 1758, Swedish biologist Carl Linnaeus developed a comprehensive system of taxonomy, as the field is known, which is still - with modifications - in use today.
Groups of closely related species belong to the same genus, which in turn are clustered into families, then orders, then classes, then phyla, and finally into kingdoms (such as the animal kingdom).
The higher up this hierarchical tree of life you look, the rarer new discoveries become - hardly surprising, as a discovery of a new species will be much more common than the discovery of a totally new phylum or class.
The 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 Dalhousie researcher Sina Adl.
"The approach accurately predicted the number of species in several well-studied groups such as mammals, fishes and birds, providing confidence in the method."
And the number came out as 8.7 million - plus or minus about a million.
Muddied waters
If this is correct, then only 14% of the world's species have yet been identified - and only 9% of those in the oceans.
"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," said Dr Tittensor.
"When we think of species we tend to think of mammals or birds, which are pretty well known.
"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."
At current rates of discovery, completing the catalogue would take over 1,000 years - but new techniques such as DNA bar-coding could speed things up.
The scientists say they do not expect their calculations to mark the end of this line of inquiry, and are looking to peers to refine methods and conclusions.
One who has already looked through the paper is Professor Jonathan Baillie, director of conservation programmes at the Zoological Society of London (ZSL).
"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.
"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."
Read more!
The primate was found in relatively untouched pockets of forest in Mato Grosso, the region that has been worst-affected by illegal deforestation and land conflicts. Julio Dalponte, the scientist who made the discovery, said it showed the extraordinary biodiversity of the area and the vital importance of conservation.
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