‘Predict and survive’ – or not

There’s an intriguing question asked in the pages of the US journal Proceedings of the National Academy of Sciences (PNAS) this week.

In a nutshell, it is this: can we forecast sudden, possibly catastrophic environmental changes by monitoring long-term trends?

As Reinette Biggs and her co-researchers point out, what can happen is that a trend gradually worsens for a while, but manageably, until there is a quick, catastrophic flip over into another state – the starkest example being from a species in existence to a species in extinction.

The term de jour for these changes is “tipping points”. And although it’s been bandied around in the arena of global warming for the last four or five years, the example this group uses in the PNAS paper involves fisheries, in particular the collapse of the Grand Banks cod stocks off the coast of Newfoundland in the early 1990s.

The collapse appears to have produced a “regime change”. Once, adult cod kept numbers of smaller fish such as capelin down by the simple expedient of eating them. The depletion of adult cod has enabled capelin to thrive – and now, they are taking their revenge by eating juvenile cod so fast that few make it to adulthood.

The predator has become prey; the ecosystem has flipped over into another “regime”, and may never return.

BBC