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Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)
It (gliding+flapping) is only viable if there are no flappers around
that can glide whenever they want to.
Why not? Yes, clearly competitive exclusion can be powerful, but do we
really expect that the simple existence of powered flyers should
completely shut down gliders with limited powered ability? It's a
reasonable hypothesis, and a very interesting one, but I don't think we
can frame it as a conclusion at this stage.
And if so, then that would seem to argue against a gliding stage in
almost every group of flyers - only insects evolved flight in the
absence of other flying animals. We might argue that pterosaurs had
sufficiently small overlap in body size with insects that they did the
same, but birds and bats certainly both appeared in the presence of
pre-existing powered flyers. I suspect that the competitive influences
are more complicated than a simple, blanket exclusion.
Yes, but there is nothing to eat there now, which is why it is empty...
But many of the pure gliders alive today compete for food with powered
flyers, as it is. I'm a bit uncertain as to why competitions
coefficients should be higher (in terms of food overlap) in the case of
incipient flapping. Incidentally, all of the living obligate gliding
taxa have planforms and/or airfoil structures that would lose
efficiency to a flapping stroke.
Quite correct. Acquiring prey by gliding simply isn't going to work
when birds are around, but commuting is always an open option if you
have a job to go to...
But animals like Draco and Chrysopelea apparently do chase prey using
gliding, in some cases - though it's not aerial hawking - they pounce
upon prey on a distant branch or tree. Of course, most birds don't
hunt by aerial hawking, either.
So I continue to maintain that the obvious "terrestrial-ness" of
Archaeopteryx, et al, is not necessarily key to the gravity vs muscle
That may be true. I'm not sure I'd frame a separation between gravity
and muscle power usage, however. Even in those groups where arboreal
stages have been critical to the origin of flight, it is quite likely
that powered leaps were involved - there is no reason to assume that
flight evolution needs to be begin with simple falls (especially for a
group such as birds, which inherited a strong leaping apparatus). This
is yet another reason why setting a threshold between arboreal and
terrestrial origins is difficult and misleading - both may actually
involve very similar launch dynamics.
Also, the debate IS a dichotomy in the sense that you HAVE to start
somewhere. Once the ball is rolling, the dichotomy disappears, but
that first step is is a booger...
Granted, but if the evolution of powered flight in a given group
involves movement between the ground and trees, or involves an intense
mosaic of both arboreal and terrestrial forms, then we will probably
never have the resolution required to pin down the ecology of the
"first" ancestor in the sequence. And besides, if that "first step"
happens to be populations that use both trees and ground running, then
the dichotomy is really broken.
Michael Habib, M.S.
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280 0181