IF YOU have nearly 100 critically endangered animals, how do you target limited conservation resources?
Australian scientists have come up with one solution, using a mathematical equation to determine which species should be saved.
The formula, devised by Queensland University experts, involves working out the benefit (in monetary terms) of an endangered species surviving, multiplying it by the chance of conservation succeeding, then dividing that figure by the programme cost. The koala, for example, is estimated to be worth $1m a year in tourism to New South Wales.
Conservation by numbers - or "survival of the cheapest" - may sound mercenary, however, proponents say it is more effective than the traditional approach, which directs money towards species at greatest risk. Already adopted by New Zealand and under consideration in Australia, it reflects the practical impossibility of saving all of Australia's threatened plants and animals.
Critics, though, are uneasy about the idea of accepting some extinction as inevitable, and they believe governments should be devoting more resources to fight to preserve the country's wildlife. They also fear that the strategy will favour "charismatic" species over, say, an obscure bat.
Australia has the world's worst record for mammal conservation, accounting for nearly one-third of all mammal extinction globally over the last 200 years.
More than 100 native plants and animals have vanished since European colonisation. The problem is global. An Australian marine geophysicist, Professor Mike Coffin, has warned that humans are on course to wipe out three-quarters of the Earth's species in the next 240 to 500 years.
Professor Hugh Possingham, director of Queensland University's Centre for Excellence in Environmental Decisions, believes many more could be saved if a "rational mathematical approach" - of which he is a pioneer - was adopted. It "tells you the best course of action to save as many species as possible," he told Fairfax Media.
A professor of both ecology and mathematics, he concedes that "prioritisation is as much about losers as winners", adding: "It's not something governments want to talk about, because in the process they have to admit they can't save everything."
In New South Wales, which adopted the strategy last month, species which would score highly include the masked owl and yellow-spotted bell frog. Those given a lower priority would include the purple-crowned lorikeet.
Calculation of "benefit" is based not only on the economic value of a species, but factors such as its role in an ecosystem. Flying foxes (large fruit bats), for instance, perform a vital function because they disperse fruit and pollinate trees.
However Belinda Fairbrother, New South Wales campaign manager for the Wilderness Society, said the idea was "grossly inadequate".