How many species inhabit the planet?

Johannesburg, March 15: Scientists and policy makers who want to slow the rate at which species are being lost face a conundrum: no one knows how many different plants and animals there are.

''Some people who study insects think there may be as many as 100 million species out there,'' said Jeff McNeely, the chief scientist at the World Conservation Union.

''But if you took a poll of biologists, I think most would say there are somewhere around 15 million,'' he told Reuters by telephone from the organisation's Swiss headquarters.

According to the Collins English Dictionary, a species is ''a class of plants or animals whose members have the same main characteristics and are able to breed with each other''.

The conundrum will hang over a U.N. conference in Brazil next week where experts will discuss ways to slow the loss of species.

The United Nations agreed in 2002 to reduce the rate at which animals and plants are disappearing by 2010.

''The implication of not knowing exactly how many species there are is that we can't tell if we are actually making progress on the 2010 target,'' said McNeely.

What we know is that around 1.7 million plant and animal species have been identified and named by scientists.

There are probably few large mammals on land left to be discovered although new deer and wild pig species were found in Vietnam in the 1990s in a region that had been heavily bombed by the United States during the war between the two countries.

Most birds have been named although new ones do crop up occasionally and a few ''extinct'' ones, such as the famed ivory-billed woodpecker of the U.S. south, have reappeared.

Biologists say there are still many plant, insect and fish species that have yet to be named.

''In southern Africa, there are between 3,000 and 4,000 described spiders. I would estimate this is less than 50 percent of what there is in the region,'' said John Leroy, co-author with his wife of a field guide to spiders in southern Africa.

Underscoring the apparent ubiquity of unnamed creatures, Leroy says unknown spiders could even be lurking in gardens.

''In Johannesburg, you could easily find a new species in your backyard, if you knew what to look for,'' he said, adding that new information on species had been collected, but much of it was gathering dust in laboratories.

The dearth of knowledge about species numbers stems in part from the fact that there are only so many qualified scientists out there who can actually name a new plant or animal. And many of those who are qualified focus on known species.

Lost Worlds

The uncertainty also highlights the fact that we have not explored the planet as thoroughly as a modern atlas may suggest.

Scientists said last month they had found a ''Lost World'' in an Indonesian mountain jungle, home to dozens of exotic new species of birds, butterflies, frogs and plants.

''Every expedition that goes into a place that hasn't been examined before finds new species,'' said McNeely.

So is there any scientific consensus on these issues? Scientists agree on the sobering fact that most species that walked, crawled, swam or flew at some point are now extinct.

Reuters