Another keystone:
I am altogether too fond of saying, “If there were no mechanism for limiting mating pool size, speciation effects would ultimately destroy the entire species and if it were a keystone species destroy the entire ecosystem.” The first part of that seems to me to be very strong. It’s not absolutely true, of course. There are a couple of other ways out. One could give up sex between individuals. Dandelions only fertilize themselves. No gene pool problem there. And trilobites were wonderfully successful for a long time, as long as all the dinosaurs combined, and they evolved very little; I suspect that they somehow had turned speciation off, or else it had never been turned on. But we like succinct statements without too many qualifications.
It’s the second part of the statement that makes me timorous. What, exactly, is a keystone species? Well it’s one that the enire ecosystem depends on. Take it out and the whole system collapses. I recently mentioned mistletoe as a keystone. That seemed a bit feeble. On the other hand, obviously today it is humans that act as the keystone. When we are gone things are going to change a lot. But calling us a keystone is a bit grandiose. We are a special case, not an example of a class of things.
My favorite I think is mammoths. (The Biosphere Rebooted Michael J. Benton NATURE vol. 471 no. 7138 March 17, 2011 page 303 reviewing Here on Earth: a New Beginning Tim Flannery Allen Lane Monthly Press 2011) These mighty beasts roamed the tundra munching away at the thin vegetation and returning organic matter to the earth in a form that let more vegetation grow. When they died out, probably because of human hunting, the landscape became much less productive, a particular blow to the hunters who were at fault.
So the mammoth’s impact is more impressive than the mistletoe but not so monumental as that of modern high tech civilization. Oh the productivity of the land is going to fall when we’re gone. Nobody else is going to be mining the phosphate or engaging in massive irrigation projects. But we are as I said a poor example. I prefer mammoths.
Besides, they were kind of shaped like a keystone depending on how you look at one.
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