> From: Toby Hemenway <hemenway@jeffnet.org>
> One reason for this, in addition to those I cited in my last post, is that
> counter-directional species usually travel alone, separate from their guilds
And another would be the thousands of years of human accelelerated
co-evolution in these agricultural ecologies. I mean, yow, oats originated
as a weed of wheat...
I recently ran across the theory that creosote bush successfully invaded N.
America an estimated 14K years ago. Now it covers a big piece of the
continent. So sometimes these invasions happen without human intervention.