Originally posted by Megalotis:
Not the case at all. This sort of limitation would be impossible to effect. In fact, man has tried with limited success to greatly expand the range of all three species through introduction of both wild-caught and captive-raised individuals. The introductions are either successful or not, based on the ability of the species to adjust to local conditions. In no case has any of the three species been able to colonise territory that is dissimilar to their native range in the eastern hemisphere.
What, for instance, stops the gray (Hungarian) partridge from moving south into central/southern Nebraska and Kansas? For some reason, after dozens of generations, the species has been unable to expand southward. Why no adaptation?
insufficent time, insuffient pressure, other reason, all the above.
Understood. However, all three species have been here (the western hemisphere) for dozens of generations. In the case of the ringneck, over 100 generations.
dozens of generation is not enough for major changes. even a slightest reading of evolution will show you that the various species evolve due to a new variation giving it an advantage over the older variation. with sufficent food, and suffecient nesting places, and sufficent things to meet their other needs, what variation would give them and advantage and lead to them moving to another unknown area?
Right, but my point was that if these species are adapting (why wouldn't they in a world of evolution) why are they unable of themselves to colonize territory over that of their original territorial expansion?
simple. what adaption would happen that would make them want to colonize another territory. to put it in simple terms, change occurs due to difficulty. man became a wonderer because the area that he was in before became cooler, and thus had less food, and it was harder to live there. as various groups expanded into different areas, they found different conditions that worked and over thousands of generation they adapted to those different conditions.
in the habatats those three species live in, there is plenty of food, plenty of everything they need. new variations would compete for the same food, etc., so would have to have to be better than the old one to show up quickly (100 generations is not that long esp in short lived species that the older generation does not compete for food with the younger one). a variation that would lead to the species changing its location would require that there be a reason for it to before it appeared. that has not happened.
An open mind is a rare and precious thing. If you agree with me, you are open-minded.
this is very closed minded. open minded does not mean agreeing with just one person. perhaps you should be open minded and agree with others.
