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Re: birds vs. pterosaurs




On Fri, 25 Jan 2002, John Conway wrote:

> I have argued before that "competition" may by the wrong term to use if 
> we are talking about replacement via speciation into vacant niches. So 
> while I agree that small pterosaurs would have continued if birds had 
> not evolved, I have argued that birds did not "out-compete" them.

Could you clarify what you mean?  If a niche is vacant, how could you
replace any species?

> It seems to me that there are two very distinct processes here: 
> ecological competition, and speciation into vacant niches. I suppose the 
> latter could be argued to be a sort of "competition", the competition of 
> speciation rates. If there are proper terms for these two alternatives, 
> I would like to know them.

Same question.

> To me, the very slow nature of the pterosaur-to-bird shift suggests that 
> ecological competition at the species level was not the prime cause of 
> the small pterosaur decline, because even a very small advantage for one 
> species causes the very rapid exclusion of its competitor.

With the exception of a couple of very artificial experiments, 
replacement, speciation, competitive exclusion, character displacement,
niche partitioning, etc., are not observable in ecological time (i.e., by
you or me).  So, we are stuck with the fossil record and the left over
"ghosts of competition past" of current speciation and niche
occupation.  So, how do you know whether these things happen slowly or
quickly?  Why shouldn't it happen both slowly and quickly depending upon
the circumstances?  Like some wars are over in a day, others grind away
for years.  Why should these biological processes move ay=t any particular
rate?  I could see it if circumstances were the same for every head to 
head contest (for example,
invasions might be expected to reach the denumen more quickly??); or if
naive species are involved.  But I would expect that creatures that are
somewhat globally distributed (i.e., not trapped on islands or
continents), who were enjoying somewhat similar niches, who flew, etc.,
might engage in eons-long dragged out arms races where the winner was
determined not by some accident but by the better (for the time and the
environment) body plan.