Wildlife Extinction Rates 'Seriously Underestimated'
Writing in the journal Nature, leading ecologists claim that methods used to predict when species will die out are seriously flawed, and dramatically underestimate the speed at which some plants and animals will be wiped out.
The findings suggest that animals such as the western gorilla, the Sumatran tiger and the Malayan sun bear, the smallest of the bear family, may become extinct much sooner than conservationists feared.
Ecologists Brett Melbourne at the University of Colorado at Boulder and Alan Hastings at the University of California, Davis, said conservation organisations should use updated extinction models to urgently re-evaluate the risks to wildlife.
"Some species could have months instead of years left, while other species that haven't even been identified as under threat yet should be listed as endangered," said Melbourne.
The warning has particular implications for the International Union for the Conservation of Nature, which compiles an annual "red list" of endangered species. Last year, the list upgraded western gorillas to critically endangered, after populations of a subspecies were found to be decimated by Ebola virus and commercial trade in bush meat. The Yangtze river dolphin was listed as critically endangered, but is possibly already extinct.
The researchers analysed mathematical models used to predict extinction risks and found that while they included some factors that are crucial to predicting a species' survival, they overlooked others. For example, models took into account that some animals might die from rare accidents, such as falling out of a tree. They also included chance environmental threats, such as sudden heatwaves or rain storms that could kill animals off.
But Melbourne and Hastings highlighted two other factors that extinction models fail to include, the first being the proportion of males to females in a population, the second the difference in reproductive success between individuals in the group. When they factored these into risk assessments for species, they found the danger of them becoming extinct rose substantially.
"The older models could be severely overestimating the time to extinction. Some species could go extinct 100 times sooner than we expect," Melbourne said.
The researchers showed that the missing factors - the number of males to females, and variations in the number of offspring - were capable of causing unexpected, large swings in the size of a population, sometimes causing it to grow, but also increasing the risk that a population could crash and become extinct.
To test the new models, Melbourne's team studied populations of beetles in the laboratory. "The results showed the old models misdiagnosed the importance of different types of randomness, much like miscalculating the odds in an unfamiliar game of cards because you didn't know the rules," he said.
For some endangered species, such as mountain gorillas, conservationists could collect data on specific individuals and plug them into models to predict their chances of survival. "For many other species, like stocks of marine fish, the best biologists can do is to measure abundances and population fluctuations," Melbourne added.
Craig Hilton-Taylor, who manages the IUCN red list in Cambridge, said extinction estimates are often inadequate. "We are certainly underestimating the number of species that are in danger of becoming extinct, because there are around 1.8 million described species and we've only been able to assess 41,000 of those," he said.
The latest study could help refine models used to decide which species are put on the red list, he said. "We are constantly looking at how we evaluate extinction risk, and it may be they have hit on something that can help us," he said.
More than 16,000 species worldwide are currently threatened with extinction, according to a 2007 report from the IUCN. One in four mammal species, one in eight bird species and one in three amphibian species are on the organisation's red list. An updated list is due to be published in October.
Next week, the IUCN is expected to highlight the dire state of the world's corals after surveying the condition of more than 1,000 species around the world.
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