K. Usry

Whether humans are the "greatest" keystone species, to me, depends on how we think of our role in the universe.

On the one hand, if we include ourselves in the natural environment and consider our influence a part of it, then in many respects human beings are a keystone species. Thanks to technology (i.e. automobiles) and infrastructure (i.e. cities and urban sprawl) our impact on ecosystems is enormous and much greater than would be expected from our "relative abundance or total biomass." Paine's theory makes no claim about keystone species having a net positive influence on the environment, and if human beings completely disappeared from the earth there would certainly be "dramatic changes to the rest of the community."

On the other hand, if we consider ourselves removed from the natural environment I think it is harder to make the claim that we are a keystone species. If human beings completely disappeared, there would be dramatic changes but the earth would eventually return to the state it was before we ever existed. In fact, Alan Weisman has written a book on the subject (The World Without Us) which outlines what would happen if human beings suddenly disappeared. Eventually all traces of human beings and society would disintegrate over time. I'm not an expert, but from what I can tell, the balance of most ecosystems doesn't depend on our existence. In this respect, we are not the greatest keystone species.