> And as far as invasiveness, corn and sunflower are native to North America, as are many of their insect pests (so their pests can't necessarily be considered as being "invasive").

My fault there. I should not have used the term "invasive" because for most people it is synonymous with "alien." The definition I was thinking of was a species, native or not, which tends to dominate or overrun other species. These are often regarded as "pests." 

The point I was trying to make is that some species are much more sensitive to changes to their environment than others, and are more susceptible to extinction. Others have traits that enable them to succeed no matter what we throw at them. That's all I meant to say.

PLB

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