Some endangered species on the brink of extinction might not be worth saving, according to a new algorithm developed by researchers at the University of Adelaide and James Cook University, both in Australia.

Dubbed the SAFE (species' ability to forestall extinction) index, the formula takes current and minimum viable population sizes into account to determine if it is too costly to save a species from extinction. The research was published online March 30 in the journal Frontiers in Ecology and the Environment.

Co-author Corey Bradshaw, director of ecological modeling at the University of Adelaide's Environment Institute, said in a prepared statement that the formula is "the best predictor yet of the vulnerability of mammal species to extinction."

The study examined 95 mammal species, 20 percent of which are endangered and 10 of which are on what the authors call "the tipping point" where they could be at the "point of no return." That tipping point, according to the authors, is a species with a population below 5,000 individuals.

Likening conservation choices to triage during wartime, Bradshaw told The Sydney Morning Herald, "During wartime, medicos have to go out and say, 'Well this guy's too far gone, we're not going to waste our time because there's too few of us.' ... We have to do the same thing in conservation, because we don't have unlimited resources, money and things that we can buy back forests or restore completely degraded ecosystems."

The authors say that conservationists could use the formula to redirect efforts toward species that are more likely to avoid extinction. "For example," Bradshaw said in his statement, "our studies show that practitioners of conservation triage may want to prioritize resources on the Sumatran rhinoceros instead of the Javan rhinoceros. Both species are critically endangered, but the Sumatran rhino is more likely to be brought back from the brink of extinction based on its SAFE index."

Other species that might not make the cut under the SAFE index include the northern hairy-nosed wombat and a flightless bird called the kakapo, which is intensely managed to prevent its extinction.

Interestingly, Bradshaw says that a species worthy of concentrated conservation efforts is the tiger, which he said "is at the 'tipping point' and could have reasonable chance of survival." But with a wild population of 3,200 split among six subspecies, the tiger doesn't quite fit his own algorithm.

The SAFE index uses information from the International Union for Conservation of Nature and Natural Resource's Red List of Threatened Species before calculating a species's chance of survival.

"I'd love to save everything," Bradshaw told the Australian Broadcasting Company. "I just don't think we can."

Photo: The critically endangered kakapo (Strigops habroptila) by Brent Barrett via Flickr under Creative Commons License