Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)

[Michael Habib <mhabib5@jhmi.edu>]

> 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 
> power debate.

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.

Cheers,

--Mike


Michael Habib, M.S.
PhD. Candidate
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280 0181
habib@jhmi.edu