Some oppose this approach, arguing that it fails to capture unquantifiable traits of the natural world, such as the psychological well-being it provides. Others say that living things are priceless.
But the idea is that it can motivate people to see natural ecosystems in a whole new way – especially people who only think about economics. “The overall goal of this concept is to get people to think holistically,” says Rebelo. “In that sense, the concept will always be useful, no matter how flawed it is. The goal is to improve management, not only for current generations but for future generations.”
So what can this approach tell us about the value of specific animals? While the majority of calculations take an overview of ecosystems as a whole, some studies have calculated the value of specific species, genera or taxonomic orders.
In 2015, BBC Earth compiled a whole series of these ratings for interactive play (the site is no longer available online, but the list is archived here). So for example, the total value of sharks for tourism is around $ 944million (£ 682million / € 799million), cow cleaning services from dung beetles was estimated at $ 380m (£ 274m / € 321m), and in Canada alone, Polar bears can be valued at $ 6.3 billion (£ 4.5 billion / $ 5.3 billion).
You could, in principle, grossly sums up the value of each of these individual animals, dividing by population. This would give a value for each of the approximately 16,000 Canadian polar bears to approximately $ 400,000 per bear (£ 289,000 / € 338,000).
But recently, Ralph Chami of the International Monetary Fund and his colleagues have applied this kind of “one animal” approach more rigorously. Their objective? To calculate the value of individual African forest elephants and great whales off the coast of South America.