We seem prone to a kind of Noah delusion: as long as we save a pair of each kind, we have fulfilled our responsibilities. But although a species that is down to its last few members is not extinct, it is not fully alive either … “Nature is not like a museum collection of the world’s species,” says Georgina Mace of University College London. “It’s not just a matter of naming and keeping every one of those things. We should care about keeping the parts of the system. Can they still interact with each other? Can they still migrate, disperse, adapt, evolve?”
Mass extinction is thus more than the loss of kinds. It’s the loss of abundance, of range, or populations. It is local extinction, the attrition of diversity as ranges shrink to enclaves, as well as global extinction. And, as the ecologist David Janzen recognized in the 1970s, it is “what escapes the eye … a much more insidious kind of extinction: the extinction of ecological interactions.”
From article by Mark Kohn in Intelligent Life, Jan/Feb 2013
Obvious to conservationists, but the first time for me to come across this perspective. Progressive fragmentation into “habitat patches” exposes the species survivors to the final decisive decay. In effect they’re already in a zoo, surrounded by humans, but without the protection of a cage.
The article also describes the mechanism by which apex predators hold an ecosystem together, and how it unravels and reorganizes once they are taken out of that system, removing more species in the process.
Wolves may protect forests by preying on the deer that browse saplings. If the wolves are wiped out, the deer multiply at the expense of the trees, preventing the forest from renewing itself: the end-point, as on the once-forested Scottish island of Rum, is a treeless landscape.
In the history of life on Earth there have been five mass extinctions, in which at least three-quarters of species were wiped out. The argument now is to what degree the extinctions of the anthropocene herald the sixth mass extinction.