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>>No animal expanding into a new niche "knows in advance" what it is going to
>>find - but a tendency to expand into an area with new food sources and fewer
>>competitors is clearly advantageous.
>But would this _compel_ the evolution of flight and all its many subtle
>anatomical adaptations? I suppose an argument could be built up in which an
>arboreal animal improves its leaping ability to a gliding stage, fills the
>trees with its successful descendants, whose existence forces improvements to
>the gliding stage within one of those descendants, whose descendants fill the
>trees with improved gliders, and so forth, until the present stage of
>unstable powered flight is attained. (There doesn't seem to be a lot more
>room for improvement in the flying abilities of modern avians.) I could get
>behind something like this scenario.

This seems reasonable except (as I have often said before, to utter silence)
I do not believe that a gliding stage is a necessary prerequisite to
flapping flight, and although there is functional overlap between gliding
and flying I think the two represent different evolutionary pathways serving
different ends.  As I suggested in another message flapping flight may
actually, in its  earlier stages, been a method of getting around within a
tree, with the ability to fly long distances between trees being a later

A thought on this - most, if not all, of the living specialized gliders are
either quite functional quadrupeds or (in the case of the flying snake)
equally able to move freely within a canopy.  Bipeds, on the other hand, may
be less adept at clambering about in trees - perhaps they are more likely to
evolve flapping mechanisms  as an assist in this?  Of course this is
probably meaningless for bats and pterosaurs, pace Kevin Padian.

>>may make it easier to feed in one area and roost or breed in another
>>(consider the Nutmeg Pigeons, that breed on offshore islets but fly to the
>>Australian mainland to feed, at times covering as much as sixty or more
>>kilometers a day).
>Yeah, I could buy that. Again, I don't know whether it would _compel_ the
>evolution of flight, but it would certainly represent an opportunity for a
>gliding or flying creature to exploit.

As noted above I think this would certainly drive flight, once it had
evolved, towards greater efficiency, but the first steps towards flight must
have been driven by the need to travel much shorter distances - a sort of
assisted leap.
Ronald I. Orenstein                           Phone: (905) 820-7886 (home)
International Wildlife Coalition              Fax/Modem: (905) 569-0116 (home)
Home: 1825 Shady Creek Court                  Messages: (416) 368-4661
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