Extinction risks vastly underestimated: study

Yahoo News 2 Jul 08;

Some endangered species may face an extinction risk that is up to a hundred times greater than previously thought, according to a study released Wednesday.

By overlooking random differences between individuals in a given population, researchers may have badly underestimated the perils confronting threatened wildlife, it said.

"Many larger populations previously considered relatively safe would actually be at risk," Brett Melbourne, a professor at the University of Colorado and the study's lead author, told AFP.

There are more than 16,000 species worldwide threatened with extinction, according to the International Union for Conservation of Nature (IUCN).

One in four mammals, one in eight birds and one in three amphibians are on the IUCN's endangered species "Red List".

In a study released on Wednesday by the journal Nature, Melbourne said the current models used draw up such lists typically look only at two risk factors.

One is the individual deaths within a small population, such as Indian tigers or rare whales.

When a species dwindles beyond a certain point, even the loss of a handful of individuals can have devastating long-term consequences, Melbourne explained.

There are less than 400 specimens of several species of whale, for example, and probably no more than 4,000 tigers roaming in the wild.

The second commonly-used factor is environmental conditions that can influence birth and death rates, such as habitat destruction, or fluctuations in temperature or rainfall, both of which can be linked to climate change.

Melbourne and co-author Alan Hastings from the University of California at Davis argue that these factors must be widened in order to give a fuller picture of extinction risk.

They say that two other determinants must be taken into account: male-to-female ratios in a species, and a wider definition of randomness in individual births and deaths.

These complex variables can determine whether a fragile population can overcome a sudden decline in numbers, such as through habitat loss, or whether it will be wiped out.

"This seems subtle and technical, but it turns out to be important," Melbourne said in an email. "Population sizes might need to be much larger for species to be relatively safe from extinction."

The new mathematical tool will be most useful for biologists who want to assess the survival prospects of species such as marine fish whose numbers can suddenly fluctuate and for which data is limited, the authors say.

Extinction threatens more species than thought
Roger Highfield, The Telegraph 2 Jul 08;

The true number of species at risk of extinction is likely to be many times higher than the current official estimate of 16,000, scientists have warned.

A new study concludes that the risk that an endangered species will disappear completely may be underestimated by as much as 100-fold using present methods.

The International Union for Conservation of Nature estimates more than 16,000 species worldwide are threatened with extinction: one in four mammals, one in eight bird species and one in three amphibian species are on the IUCN "Red List."

Today, a warning that the figure may have to be revised sharply upwards comes from a study led by Dr Brett Melbourne of the University of Colorado, Boulder. A mathematical "misdiagnosis" has created the wrong impression that above a relatively small population size, extinction is unlikely.

The authors conclude "extinction risk for many populations of conservation concern needs to be urgently re-evaluated."

Dr Melbourne told the Telegraph that the finds do not mean that 100 times more species are now at risk but said the overall number, once the details are understood, "should be revised up by a large amount."

Although this work might not affect estimates of the risk of high profile endangered species like mountain gorillas, where biologists can collect data on specific individuals to help develop and track extinction, it will apply to many other species, like stocks of marine fish, where the best biologists can do is to measure abundances and population fluctuations.

"I'm reluctant to mention particular species because each case will be different and one would have to analyse the data for that species," he said. The study will also lead to a revision of research published four years ago, also in the journal Nature, that warned a million species worldwide are threatened with extinction by climate change over the next half century.

The new study suggests that the shifts in the distribution of some species, such as amphibians, grasses, migratory birds and butterflies will have a much bigger effect on the variety of life.

Dr Melbourne said current mathematical models used to determine extinction threat, or "red-listed" status, of species worldwide overlook random differences between individuals in a given population.

Such differences, which include variations in sex ratios as well as size or behavioural variations between individuals that can influence their survival rates and reproductive success, have an unexpectedly large effect on calculations of extinction risk.

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

"By accounting for random differences between individuals, extinction rates for endangered species can be orders of magnitude higher than conservation biologists have believed."

"Almost all previous studies don't include all of the factors we studied, so it is fair to say that most previous studies suffer from this inadequacy. One general message from our work is that population sizes might need to be much larger for species to be relatively safe from extinction."

The study is published today in Nature with Prof Alan Hastings of the University of California, Davis and places greater emphasis on sex ratio variations and physical variation between individuals within a population.

"There has been a tendency to misdiagnose randomness between individuals in a population by lumping it with random factors in the environment, and this underestimates the extinction threat" said Dr Melbourne.

To confirm their thinking, the researchers monitored populations of red flour beetles - Tribolium castaneum - in laboratory cages, showing that the old models underplayed the importance of different types of randomness, so called stochastic effects, much like miscalculating the odds in an unfamiliar game of cards because you don't understand the rules, he said, adding "the effect we have uncovered here will be larger in natural populations."

The paper concludes: "Our results demonstrate that current estimates of extinction risk for natural populations could be greatly underestimated because variability has been mistakenly attributed to the environment rather than the demographic factors."

Wildlife extinction rates 'seriously underestimated'
Ian Sample, The Guardian 2 Jul 08;

Endangered species may become extinct 100 times faster than previously thought, scientists warned today, in a bleak re-assessment of the threat to global biodiversity.

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.