Life on earth facing an extinction crisis says study

By STEVE CONNOR

Life on Earth is facing an extinction crisis that could be far worse than previously thought, say two leading ecologists who have studied the rate at which animal populations are being lost.

The scientists have found that the geographical ranges of 173 species of mammals have declined, collectively, by more than 50 per cent over several decades, indicating a severe constriction of breeding territories.

Paul Ehrlich of Stanford University in California and Gerardo Ceballos of Mexico University believe that the loss of viable breeding populations has often been overlooked.

"The loss of species diversity has correctly attracted much attention from the general public and decision-makers," says Professor Ehrlich.

"It is now the job of the community of environmental scientists to give equal prominence to the issue of the loss of population diversity.

"We are talking about nothing less than the preservation of human life-support systems. We neglect the issue at our peril."

Studies of biodiversity should take into account the number of endangered populations of breeding animals in a species, and not rely on identifying extinct species, the scientists said.

In the journal Science they write: "Most analyses of the current loss of biodiversity emphasise species extinctions and patterns of species decline, and do not convey the true extent of the depletion of humanity's natural capital ... We need to analyse extinctions of both populations and species."

Professor Ehrlich and Dr Ceballos compared the territories of existing breeding populations of 173 mammal species living on five continents with historical records of the known distribution.

Their data showed that in many cases, species thought to be widely distributed had been reduced to scattered remnant groups over the same area.

The North American brown bear and grey wolf, and the Asian tiger are examples of animals whose ranges may be far smaller than suggested by official maps.

"We suspect that many less prominent species ... have lost portions of their ranges but without detection because they have not been subject to intensive mapping attempts," the scientists say.

The study reveals wide differences between how species resist human interference. All wild populations of Pere David's deer from China, for instance, have become extinct, whereas the spotted hyena has lost only 14 per cent of its populations despite large loss of its natural habitat.

Africa and South-east Asia suffered some of the largest losses.

"Population extinctions today seem to be concentrated either where there are high human population densities, or where other human impacts ... have been severe," the scientists said.

"Australia, which is the continent with the largest number of mammal species extinctions, is also a continent showing a widespread severe reduction of populations."

Some species, such as the black and Sumatran rhinos, are threatened further because most or all of their breeding populations are in one country and they are vulnerable to the effects of political instability.

- INDEPENDENT


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