Biologists have suggested a mathematical model, which will hopefully predict which species need to be eliminated from an unstable ecosystem, and in which order, to help it recover.

The counterintuitive idea to kill living things for the sake of biodiversity conservation comes from the complex connections presented in ecosystems. Eliminate a predator, and its prey thrives and shrinks the amount of whatever it has for its own food. Such “cascading” impacts along the “food webs” can be unpredictable and sometimes catastrophic.

Sagar Sahasrabudhe and Adilson Motter of Northwestern University in the US have shown that in some food web models, the timely removal or suppression of one or several species can do quite the opposite and mitigate the damage caused by local extinction. The paper is described in Nature magazine.

The trick is not an easy one, since the timing of removal is just as important as the targeted species. A live example Sahasrabudhe and Motter use is that of island foxes on the Channel Islands off the coast of California. When feral pigs were introduced in the ecosystem, they attracted golden eagles, which preyed on foxes as well. Simply reversing the situation by removing the pigs would make the birds switch solely to foxes, which would eventually make them extinct. Instead, conservation activists captured and relocated the eagles before eradicating the pigs, saving the fox population.

Of course conservation scientists are not going to start taking decisions based on the models straight away. Real ecosystems are not limited to predator and prey relationships, and things like parasitism, pollination and nutrient dynamics have to be taken into account as well. On the other hand, ecosystems were thought to be too complex to be modeled at all some eight years ago, Martinez says. Their work gives more confidence that it will have practical uses in nearest future.