Numbers up for beasts at vanishing point

IT is a sad fact that all tigers are endangered, so this is as close to one of these magnificent beasts as Iadine Chades may get.

IT is a sad fact that all tigers are endangered, so this is as close to one of these magnificent beasts as Iadine Chades may get.

On leave from the French National Institute of Agriculture's Toulouse laboratory, she has brought specialised skills to a University of Queensland investigation into the management of rarely sighted, or cryptic, species such as Dreamworld's bengal tiger, Mohan.

"Actually, I come from artificial intelligence research and this is the first time we have used these methods to solve (such) problems," Chades says. There are, she says, "quite similar problems in biology and ecology, highly complex".

She applies the partially observable Markov decision process, an established mathematical model used for robot navigation and machine maintenance, among other things.

The aim is to work out when to conclude cryptic species are no longer living in any given area and it is time to abandon management programs, such as patrols to deter poachers. The trick is that even though cryptic species may not have been sighted in a long time, they may not be extinct.

Also, it can be hard to formulate a plan of action when it is difficult to observe the species. "The more threatened, the less easy they are to observe," Chades says.

The algorithm factors in elements, each of which has been assigned a numerical value, such as information on the size of the species population in an area, detectability, the cost of implementing patrols and the cost of monitoring, as well as the monetary value of the species.

Chades and UQ's Eve McDonald-Madden, worked with the university's Ecology Centre director Hugh Possingham and others on the project using data from a population of Sumatran tigers -- all tigers are endangered and cryptic -- and their findings were recently published in the Proceedings of the National Academy of Sciences.

"A species such as the tiger is likelier to be assigned a higher monetary value because they are big and charismatic, and potential for tourism is another element that (may) boost value," McDonald-Madden says.

There are three potential outcomes: managing an area, for example with patrols; monitoring the area to establish if the species is still there; and doing nothing, effectively withdrawing support for the species.

They conclude that if, for example, the species is highly valued, managing a protected area can be the best thing to do even if it is uncertain the species is still present. But if a species remains unsighted for long enough, belief in its existence may decline to the point managers decide to shift resources to merely surveying.

But the study shows that if a species has not been sighted during surveys over seven years or more, it is probably time to give up.