(Image: Claus Meyer/Minden)
In a slow-motion apocalypse, half of the animals on the planet are shuffling towards oblivion. But we still have time to swing into action to save them
BETWEEN a third and a half of all species will go extinct⊠by the year 2000. That was the dire prediction made in the 1980s. Thankfully, it was wrong. While , only â at least in well-studied groups such as mammals and birds.
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But donât go sighing with relief just yet: the main problem with this prediction may be the timing. There can be a long lag between cutting down a forest, say, and losing the species that lived there. Decades or even centuries may pass before the extinction follows. Put another way, many of the species around today may be the walking dead.
Take the golden lion tamarin. A member of the marmoset family, it is native to the coastal forests of Brazil. Only 1000 or so are left, trapped in the few fragments of forest that remain. Such small, isolated populations are essentially doomed: even if the forest fragments survive, sooner or later dwindling gene pools or disasters such as forest fires and disease outbreaks will wipe them out.
Luckily for the tamarins, conservationists are trying to stop this happening. For instance, Stuart Pimm noticed that a 100 hectares of cattle pasture was all that separated one of these isolated groups from a much larger patch of forest nearby. So in 2007 he set up a charity, , to buy the land and reforest it. Within just six years the golden lion tamarins began to exploit this âmarmoset motorwayâ. Even as saplings, the new trees already provide the protection from ground predators that tamarins need to travel. There are plans to create more corridors (see map)
âWithin six years, the golden lion tamarins started using the âmarmoset motorwayââ
Efforts like this are greatly boosting the tamarinsâ survival chances. The point is that although half of all species really may be heading for extinction, it is not too late to save them. âIf extinction is a slow process then you do have time to do something about it,â says Rob Ewers, a conservation scientist at Imperial College London.
While the tamarinsâ plight was clear, working out which of the worldâs species are in trouble is not always easy. We still donât even know how many species there are, after all, let alone where most live and what they need to survive. Many of the factors that will determine their fate, from the severity of poaching to the introduction of invasive species, are not really predictable.
The greatest threat to plants and animals, though, is habitat loss, which can be measured. To work out the resulting species loss, biologists have turned to an ecological rule of thumb called the species-area relationship: a way of estimating the number of species in a given area. âThe reason it works is that if youâre in a 10-hectare area of forest itâs likely to be more or less all the same,â says Ewers. âIf you go to 100-hectares of forest youâre more likely to encompass a ridge and a gully. If you go to 1000 hectares, you might have a lake system in there; you might have a small mountain.â More area means more variety, which is always good for diversity.
While the species-area relationship might work for pristine areas, using it to estimate extinctions has become controversial. This was the method used to produce the half-of-all-species-gone-by-2000 prediction, and some argue that it always overestimates extinctions. Others argue it . Paradoxical as it sounds, both views may be right â it all depends on the time scale.
For instance, Stefan Dullinger and Franz Essl, conservation scientists at the University of Vienna, Austria, and their colleagues recently looked at how many plants and animals are threatened in 22 European countries. They compared this with factors linked to habitat loss, such as population density, GDP and land-use intensity over the past century. They found that what was happening around 100 years ago was a better predictor of todayâs extinction rate than what is happening today.
In other words, there can be a long time-lag between habitat loss and extinction: species are being lost today because of what happened a century ago. When habitat is lost, only a few species may go extinct straight away. But an is created that results in many more disappearing over the following decades and centuries. âAs socio-economic activities in Europe continue to increase, the debt is increasing in scale,â Essl says.
Whatâs more, says Dullinger, simply preventing any further habitat loss isnât enough to protect Europeâs endangered species. âPreserving the status quo will not halt species loss, which will continue until the debt is paid,â he says.
What causes the lag? When, say, an area of rainforest in the Amazon is cut down, many animals will escape to neighbouring areas. But with less food to go round, they cannot all survive. Population sizes will fall, and the smaller a population becomes, the more vulnerable it is to being wiped out by random events. âLow population sizes are just unsustainable,â says Ewers. âSomething happens â your dominant male is infertile, or a jaguar comes through and eats all the babies that year, but it takes time for those events to accumulate to drive you to extinction.â
How long? In the 1970s, biologist Thomas Lovejoy persuaded cattle farmers clearing forest in the Amazon to help him find out. Lovejoy arranged for 11 islands of forest, covering 1, 10 or 1000 hectares to be left intact, but completely isolated from each other.
Three decades on, it was very clear that the rate of loss depended on the size of the habitat (). âWith 1000 hectares it was taking decades for species to be lost,â says Pimm, a conservation ecologist at Duke University in Durham, North Carolina, who was involved in the project. âBelow 100 hectares itâs pretty brutal,â he adds, taking less than 15 years for a forest fragment to lose half of its species. âIf you get down to a hectare or 10 hectares, the species go within a year or two,â he says.
The failure to take into account these lags, then, may be the main reason why some predictions based on the species-area relationship appear to have got it so wrong. Instead, Ewers and his colleagues have developed an alternative approach that predicts both the scale and timing of extinctions, based on studies of about 50 sites across the world.
They applied this to the Amazon, where about 1 per cent of animals like birds, mammals and amphibians had been lost by 2008. Their conclusion was that these extinctions are only a fifth of the number we can expect due to the deforestation that has taken place ().
That may not sound too bad, but of course deforestation has not stopped. If it continues at its current rate, the team calculates 40 per cent of species will be lost by 2050. That is the actual loss expected by 2050, not counting the remaining extinction debt.
Only time will tell if these recent predictions will prove to be more accurate than those made in the 1980s. But there are reasons to think they are underestimates. For starters, Ewerâs method does not include factors like global warming, which will be bad news for species trapped in isolated pockets, unable to migrate to a place with more suitable conditions.
Nor do predictions of this kind include the effects of invasive species, like the grey squirrels pushing out the UKâs native red squirrels. Their full impact may only become clear after centuries or millennia, in part because of knock-on effects due to the linkages between species. On New Zealandâs North Island, for instance, the introduction of rats wiped out local populations of birds including the bellbird and stitchbird. In 2011, biologists discovered that these birds play an important role in pollinating the flowers of the shrub Rhabdothamnus solandri. With the birds gone, the plantsâ numbers are slowly declining.
For biologists, though, the whole point of studying extinction debt is not to produce gloomy headline figures about how dire the situation is. Instead, it is about understanding which species are most at risk and whatâs needed to save them. âExtinction debt is a window when you can see that your actions have done something, but itâs not yet fatal, so youâve got an opportunity to get in there and be proactive,â says Ewers.
âItâs a real problem with conservation â everyone wants to talk about how weâre all going to die,â says Pimm. âThe fact is, yes, we know how fast species are going extinct, but I spend most of my days looking for solutions â and there are solutions.â
These include creating wildlife corridors that help maintain genetic diversity, as the Saving Species charity is doing to save the golden lion tamarin. âI am very proud of this example,â Pimm says. âIt basically pokes extinction debt in the eye and says âWeâre not going to have thatâ.â
âWe poked extinction debt in the eye and said: âWeâre not having thatââ
Once an extinction debt has been identified, a species becomes easier to save. Take R. solandri. Conservationists plan to reintroduce the pollinating birds, which survive on nearby islands. Because the shrub can live for a century or more, there is still time to save it.
Ewersâ work, too, shows there is still a window of opportunity to save many species in the Amazon. Applying environmental laws more stringently could reduce the extinctions to 30 per cent by 2050, rather than 40 per cent, his team calculated. Greater efforts to save forests in key areas could limit it to 15 per cent. âThose kinds of interventions have a real positive effect. When you extrapolate out to 2050 you can see â itâs a different future,â says Ewers.
So what can we take from all of this? The clearest message from these studies seems to be that we have made a shocking mess of the worldâs biodiversity, but â importantly â it doesnât have to be all doom and gloom just yet.
As Ewers points out, we have put quite a lot of effort into destroying species,. âIt is hard to drive a species extinct,â he says. âThey donât just fall over and die, youâve really got to work pretty hard to knock them out.â
So perhaps itâs time to start working just as hard in the opposite direction. And the sooner the better.
This article appeared in print under the headline âGolden opportunityâ
