A question for the fishologists on here

[smokepoles]

I lived in Maine for a couple years and Alabama for a couple years. Many of the creeks and rivers in these places have solid small mouth, pike, walleye and some panfish populations. Especially small mouth seem able to adapt. So why have, say the small mouth, never pushed up the Weber and established. Or pick your species and moving body of water with the same question.

I have a few theories I suggested when Cookie asked me but I figured I would ask the great masters of fishology here for your thoughts.

Tight lines

Though not an ichthyologist, I believe that in general the intermountain rivers are cold water habitats not altogether favorable in environment and forage for the warm water species you mention.  There is of course some overlap especially where we have intervened with dams and reservoirs that alter the environment such that the warm water species can survive in rather localized areas.