Maths glitch behind underestimating species extinction rate

Current maths models being used to determine the extinction threat overlook random differences between individuals in a given population, according to Colorado University's Brett Melbourne, co-author of the study.

"When we apply our new mathematical model to species extinction rates, it shows that things are worse than we thought," said Melbourne.

Currently, extinction risk models are based on two factors, said Melbourne. One is the number of random events adversely affecting individuals within a population - the accidental drowning of a rock wallaby, for example.

While a sequence of such random events in a small population can have a big impact, such events are far less likely to affect larger populations, Melbourne said.

The second risk factor used in extinction models is the impact of random events like temperature and rainfall fluctuations that can influence birth and death rates of individuals in a population, said Melbourne.

But two additional factors highlighted by researchers - sex ratio variations and physical variation between individuals within a population - have been ignored or misdiagnosed by most extinction risk modellers, he said.

For some large, endangered species like mountain gorillas, biologists can collect data on specific individuals to help develop and track extinction trajectories, he said.

"We suggest that extinction risk for many populations of conservation concern need to be urgently re-evaluated with full consideration of all factors contributing to stochasticity, or randomness," the authors have written in the latest issue of the journal Nature.

According to a 2007 report by International Union for Conservation of Nature, a network of about 1,000 bodies with thousands of scientists, more than 16,000 species worldwide are threatened with extinction. St/jg

(336 Words)03071109NNNN (IANS)

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