Science - September 1, 2011

8,700,000 species on earth

The earth is estimated to be home to 8.7 million species, most of which we do not know yet. This claim was made by a group of Canadian scientists last week in Plos Biology. Is it a realistic estimate?
'Yes', says Wageningen plant taxonomist Jan Wieringa. '8.9 million is more likely to be the lower limit than the upper one.'

We now know of 1.7 million species, or 20 percent of the estimated 8.7 million.  Previous calculations varied between 3 and 100 million species. I don't think this is a bad estimate. We often visit Gabon and we have sometimes made estimates there too. There are now 5,000 higher plant species known there. Using similar formulae, we think that there must be about 7,000 plant species there. So we know about 70 percent of them. But for insects the proportions are sometimes the other way round and when it comes to nematodes, even less is known. The smaller the creature or plant, the less known. Although I did find a new species of the pulse family a couple of years ago in Gabon - a giant of the forest that had not been identified before. On our last expedition one in every hundred plants we collected was a new species. Then we start selecting, I can tell you. If you really search, you find more.'

'Last year I found a strange species of grasshopper when I was on holiday in Italy. On two counts it was very different to the familiar species. But I could only find one specimen. So I decided: this is a mutation and not a new species, but perhaps I am wrong. Every year, 15,000 new species are described. With the new DNA techniques, it is easier to prove that it is a new species.'

Research shows that one quarter of the species will become extinct in the next century thanks to climate change. About 2.2 million. Is that true?
'No, far more species are going to die out. One quarter of the species we know are likely to die out. The species that we don't know are probably even more threatened. Most of them are rare or have a small distribution area where we haven't looked properly yet. But in the history of the earth, large groups of animals and plants have died out before. Usually that is followed by an increase in biodiversity, because other species get more space. But that is a question of millions of years, whereas the extinction will happen in a couple of decades.'

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