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Re: BCF vs BADD



>I am not seeking to be critical, but I wonder if a bird has the time
>(evolutionary speaking) to evolve into a larger size and not be so heavily
>preyed  upon; while evolving, that the population cannot sustain itself. Is
>not one of Dr. Gould's hypotheses in his theory of "puncuative equilibrium"
>(my spelling will get me on this one),  that isolated populations are more
>likely to evolve into new species?  It would seem to me that a likely
>scenario would be an isolated population that is being selected for increased
>size to take advantage of new prey resources at a time that they have no
>predators themselves.  
>
>Dr. Thomas R. Dix  

This is valid if the large bird is effectively defenceless as it loses
flying ability.  I do not think this is possible either.  What I am
suggesting is that increased size, limb length etc in a line of flying birds
could reach a stage at which flight became no longer necessary as a prime
defence - something we already see in  number of ground birds, not all of
them large, that fly only rarely.  The heaviest flying bird, the Kori
Bustard of Africa, is a pretty good-sized creature.  Bustards (particularly
the smaller ones) are also extremely cryptically coloured, and their chief
method of  defence is concealment among vegetation where they can be
extremely hard to see.  A combination of size, speed, camouflage and other
ground-based defences could make flight unnecessary, and as the maintenance
of unnecessary structures is energetically costly they may be lost in
consequence - especially if selection is driving the bird towards larger
size.  Once flightlessness and large size are achieved the lineage may (as
in the dromornithids) produce even larger graviportal descendants.  None of
this needs to happen in predator-free areas.
--
Ronald I. Orenstein                           Phone: (905) 820-7886 (home)
International Wildlife Coalition              Fax/Modem: (905) 569-0116 (home)
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