Extinction, Slime, and Bottoms

Open access, freely available online T here is an old Chinese curse: 'May you live in interesting times.' According to those who know about such things, we live in a momentous time, the time of the Sixth Mass Extinction! But most of us do not feel at all cursed. Because, in fact, the Sixth is quite different to the previous Big Five—no-one would notice this one if we were not repeatedly reminded of it by ecologists. Previous mass extinctions were not so bashful, so discreet. The fossil record reveals the disappearance of pollen during previous ones, replaced by an abundance of fungus spores, telling us of a world of devastated forests rotting away. The earliest sediments after the mass extinction that did away with the dinosaurs are barren of fossils: so it is not just that species were going extinct, conditions for life itself were bad. Not only did species diversity drop, the abundance of life did as well. But conditions for life itself have never been better than today. In the history of the planet, there has never been anything as productive of life as a wheat fi eld in Kansas. It may not have a large diversity of species, but that is a different matter. In fact, one of the reasons for the ongoing loss of plant diversity from grasslands is the very reason the wheat fi eld is so productive—fertilisation. We are pouring nitrogen fertiliser into the environment and, through the well-studied 'paradox of enrichment', this reduces species diversity while increasing actual biomass. Now, there is no question that if current trends of habitat alteration and climate change continue then we will ultimately lose large numbers of species—diversity will drop—but this does not necessarily translate into a loss of abundance of life, and that is a big difference between now and previous mass extinctions. Looking at specifi c groups of organisms tells the same story. So, for example, many island bird species are threatened, like the kagu of New Caledonia, but British seabird populations, like puffi ns, are booming. Worldwide amphibian diversity is threatened, but cane toads are a pest in Australia. Introduced species pose a threat to diversity—the 'McDonald-isation' of nature—precisely because they achieve enormous abundances. Actually, all six mass extinctions may have one very important thing in common: from the point of view of the vast bulk of life on the planet they are probably …