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

don ohmes wrote:
Perhaps "competitive exclusion" has some modern meaning I am unfamiliar with, so I will substitute the term 'competitive superiority' in it's stead.

That would be a different situation altogether. Competitive exclusion simply refers to the expectation that the coefficient of competition and the coefficient of selection will be negatively correlated over a given time interval for a specific interaction set. Tests of this expectation have met with mixed results. It clearly matters in many cases, but may not dominate in others.

It is an essential component of the natural selection concept, and a reality familiar to everyone.

Familiarity does not equate with applicability. Besides, I never said exclusion was unimportant (in fact, I stated the opposite).

Mechanics are only relevant to evolution from the perspective of natural selection, so it is considerably more accurate to say "Mechanics are notoriously difficult to demonstrate, in fact, and it is still uncertain how important they are in determining specific evolutionary patterns."

Not true - mechanical constraints are often easy to quantify, are very dependable metrics for certain problems, and have been demonstrated convincingly to be a major aspect of biological evolution both in modern populations and through evolutionary history.

True, but sometimes theory is misleading. Solar thermal power is more "efficient" than photovoltaic panels (PV), for example. So when Google funded (partially) a 720 acre solar power plant in the Mojave they naturally went w/ solar thermal. However, the concentrators must be washed w/ water twice a week to maintain that "efficiency"!!!

Yes, sometimes expectations are not met. If you can demonstrate where I (and others) have made an error regarding the expected breakdown of vorticity from flapping in most obligate glider planforms, then go for it. The fluid dynamic equations are pretty robust, though.

No flying squirrel will ever increase glide length by waving it's paws in mid-flight, but it is possible for selection to enhance control motions that occur at the end of the glide.

Quite possible. There are also possibilities related to scrambling, launching, and prey capture that could introduce flapping modes. It's also quite possible that ancestral bats differed in critical details from flying squirrels, in terms of planform and airfoil anchoring. Until we have more information on the base of Chiroptera, these are idle speculations at best.

I did not say that there was no competition. I continue to assume that the competitive barriers faced by proto-birds as they achieved lift-off were less than they would face in an environment filled w/ real birds. And bats.

Quite possibly.

Heh. Oh, do you have an example of "terrestrial origins for flight"? :D

As mentioned before, birds may very well be an example.

Or not. There is debate about that... :D

Question: if you were going to attempt to falsify an arboreal origin for flight in a given group, how would you go about it? Your argument that Archaeopteryx could maybe, possibly climb things and use them for elevated leaps is fine - but it's also a sort of special pleading. The outgroups to birds are terrestrial, the most basal birds appear to have limited arboreal adaptations (if any), and birds have several exapted traits that could make terrestrial launch possible (not to mention the work on incline running). There might still be a mosaic of arboreal and terrestrial stages mixed into the origin of avian flight (incline running models, especially, suggest this), but that seems about as far as we can go with it.



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