Survival strategy - Can the dinosaurs' demise show us how to save the Earth?
点击量： 时间：2018-02-14 05:01:10
By Roger Lewin ECOSYSTEMS around the world recover from mass extinctions in curiously different patterns, reports a palaeontologist from the University of Chicago. He says that further study of this effect might help us predict, or even prevent, the long-term impact of species extinctions and invasions that are taking place today. Not long ago, mass extinctions were dismissed as having little impact on shaping the overall pattern of long-term evolution: they were a mere blip in life’s flow. Then scientists realised that normal Darwinian rules are tossed aside during mass extinctions. So species that are perfectly well adapted to ordinary life may still be obliterated. Most biologists believed that the greater the intensity of the collapse, the more vulnerable the afflicted ecosystem is to subsequent invasion by alien species. But in last week’s Science (vol 279, p 1327), David Jablonski of the University of Chicago has shown that in fact there is no clear link between extinction intensity and the level of invasions. Furthermore, the size of the extinction does not predict the extent of post-extinction recovery. “I didn’t expect to find this,” says Jablonski. “It suggests that the whole process is much more complex than we thought.” Jablonski studied the fossil record for molluscs—including clams, snails, scallops, whelks and oysters—from the 10 million years following the demise of the dinosaurs, around 65 million years ago. He chose locations near the tropics (northern Africa, Pakistan and northern India) and some more northern regions (the Gulf coast of the US—that is, Texas, Louisiana, Mississippi, Georgia—and northern Europe). In each of these regions, life bounced back rapidly and vigorously. There was “a pulse of species origination after the extinction boundary, whose effects are still seen in the modern biota, like the echo of the big bang”, as Jablonski puts it. However, recovery in the Gulf coast region was much more patchy than it was elsewhere. Not all species recovered, while some bounced back very rapidly within four families, known as bloom taxa. Many more alien species migrated into the Gulf coast, too, compared with the other regions. Because the degree of species loss during the extinction had been uniform in all regions, something else must have enhanced the “post-extinction scramble for ecological opportunity” in the Gulf coast region, says Jablonski. Just what that factor might have been remains a mystery. Perhaps it was because the Gulf coast was in the path of the comet that hit the Yucatan peninsula at Chicxulub from the southeast. If the comet wiped out different kinds of species in the Gulf coast—including perhaps some that played a vital role in maintaining the dynamics of the ecosystem—then post-extinction recovery in the region might also be different. Jablonski says these results may help us cope with modern-day extinctions, in which humans have a prominent role, both by destroying habitats and by introducing alien species. For instance, a greater understanding of recovery processes would improve our ability to predict, or even ameliorate,