THE EARTH literally teems with life, with species occupying every possible nook and cranny of the biosphere. Now scientists have produced a head count for life on our planet, estimating it supports 8.74 million distinct species.
This includes all the plants, animals and insects of the land and all the creatures that occupy the oceans, lakes and rivers. It also includes fungi, moulds, algae and certain single-celled organisms.
Yet so far scientists have only been able to catalogue 14 per cent of this abundance, or 1.22 million species. This leaves 7.52 million species yet to be discovered.
This new estimate prepared by researchers at Dalhousie University in Halifax, Canada and the University of Hawaii is published this morning in the open access journal Public Library of Science Biology( PLoS Biology). Previous estimates have suggested this species count could be as low as three million or as high as 100 million.
The scientists went for a much lower estimate, however, and in their report described how they did it. They studied the 1.22 million known species found in the Catalogue of Life and in the World Register of Marine Species. These make use of the classification system first developed by Carl Linnaeus in 1758 and still used today to name and describe species.
The team found numerical patterns hidden within these catalogues of life and the patterns allowed them to estimate the species count. They set this at 8.74 million – give or take 1.3 million either way. This allows a range of between 7.4 million and 10 million species.
About three quarters of all the species are found on land while one quarter dwell in the oceans.
The identification of more species is becoming increasingly urgent given that human activity is driving many species rapidly towards extinction.
“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 lead author Prof Camilo Mora.
Fellow author Prof Boris Worm argued that if a country didn’t know its population to within a million or even 10 million, then how was that country to 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,” he said.
Equally startling is the fact that the Red List – which names almost 60,000 animals either threatened or facing extinction – represents less than 1 per cent of the catalogue of world species.
“The scientists are right in saying there are a lot more species yet to be discovered,” ecologist Dr Eugenie Regan of Ireland’s National Biodiversity Data Centre said yesterday.
“Biodiversity is huge yet our knowledge of the number of stars in the universe is better, we know how many stars there are but we don’t know the number of species. If you don’t know what you have you don’t know what you are losing.”
Ireland has 31,000 land and marine species catalogued with an estimated 10,000 yet to be discovered, according to a study released earlier this year by the centre.
“We are part of the world, we are part of biodiversity. We are part of that web and we need to protect it,” Dr Regan said.
“The rate of [species] loss is certainly more rapid than the rate of species discovery,” said University College Cork’s registrar and professor of zoology and ecology Prof Paul Giller. “There is a danger in losing species because we don’t know what consequences these losses will have,” he said.
Some “keystone” species help to hold ecosystems together but we don’t know which species are essential because so many have yet to be discovered.