MANY ecosystems face meltdown as global warming gathers pace. A new study suggests that fewer species than expected will become extinct鈥攂ut they are set for a turbulent time as the ecosystems they live in become unrecognisable.
Conventional models of warming assume that most species and ecosystems will migrate gradually towards the poles or up mountainsides. 鈥淭hat is too simplistic,鈥� says A. Townsend Peterson of the University of Kansas, who has investigated the likely effects in Mexico, a major centre of biological diversity. 鈥淭he effects will be a lot more complicated, and often a lot more drastic.鈥�
In reality, complex communities of species with intimate relationships with each other will be blown apart, with highly unpredictable results. Climate change will 鈥渂ring together new hosts and parasites, new predators and prey鈥�, says Peterson. Under such circumstances, the actual changes in temperature could be the least concern for many species.
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Peterson鈥檚 conclusions are based on a detailed analysis of what climate change could hold for some 1800 species of birds, mammals and butterflies in Mexico. He has mapped the current geographical range of each by combining records from collections held in natural history museums around the world with software that can identify the species鈥� ecological niches. And he has used simulations of likely climate change to plot where species might end up in 50 years鈥� time.
The result is a lot more complicated than conventional predictions based on climate alone. The greatest disruption to individual species, he says, may come from the 鈥渞eshuffling鈥� of ecosystems rather than the warming itself.
Take one species, an endemic Mexican bird called the West Mexican chachalaca, which is something like a cross between a turkey and a pheasant and is named after the sound of its loud cry. If climate were all that mattered the bird might expand its range by up to 75 per cent, says Peterson. But in the real world, the bird will probably lose about a quarter of its habitat and be holed up in the foothills of the Sierra Madre del Sur.
The good news is that, while up to a fifth of Mexico鈥檚 endemic species may lose most of their range, many fewer are likely to become extinct than had been feared. The bad news is that the ecological changes in many places could be catastrophic. As old ecosystems disappear, new ones with unknown properties will emerge, says Peterson.
In some places in Mexico, the 鈥渢urnover鈥� of species will exceed 40 per cent, as dozens disappear or are displaced by invaders. This kind of ecological meltdown is likely in the Chihuahua desert and the Baja California peninsula in the north, he says. Meanwhile, some mountain areas could become 鈥渞efugee camps鈥� for displaced species.
The findings raise questions about the effectiveness of plans being devised by conservationists to protect wildlife during climate change by creating natural 鈥渃orridors鈥� through which animals and plants can migrate as temperatures change. If Peterson is right, then the corridors will be chaotic places full of unexpected perils.