[Taxacom] Dispersal... again

[Kenneth Kinman]

Michael,    
       I am not sure Mayr would have restricted vicariance just to the
Pleistocene, even in the 1940s, and certainly not once plate tectonics
starting taking hold in the 1950s and 1960s.  And your suggestion that
"many authors" still use such a model seems unbelievable to me (who are
some these "many authors" to which you refer?).                 
       In any case, as evidence for plate tectonics and continental
drift accumulated, Mayr accepted more cases of vicariance, such as when
it became clear that North America and Europe were connected relatively
late in time  (compared to the drift of South America from Africa).            

        However, I think he would agree that the pendulum has swung too
far in the other direction, and that some pangeographers have overshot
the mark and began proposing vicariance hypotheses far too much, so much

so that when long-distance dispersal evidence is presented, such
panbiogeographers seem to automatically object (in what I call a
knee-jerk reaction), and over exaggerate problems with molecular clocks
and the fossil record.  John Grehan in particular seems to exaggerate
problems with molecular clocks and suggesting long fossil gaps, even
when such exaggerations stretch credulity (as in the case where he
objects to Nile crocodiles dispersing across the Atlantic).     

       And selectively bashing Mayr for what he wrote in the 1940s
(before plate tectonics was well documented or understood) seems like a
cheap shot.  The avian fauna of Australasia is no doubt more a result of

vicariance than was realized back in the 1940s, but that is no reason to

now minimize the evidence of dispersal either.  I really hate it when
the pendulum swings too far in the opposite direction (or present-day
researchers overly criticizing what was published over 60 years ago).         
 
       Anyway, I feel more comfortable criticizing John Grehan in some
of his present-day knee-jerk reactions than trying to retroactively
criticizing Mayr for being conservative in what aspects of plate
tectonics he accepted as evidence accumulated during the 1940s through
1960s.              

      Most importantly, that vicariance was underestimated during the
1940s is no excuse for overestimating vicariance in the present.  It
sort of reminds me of the paraphyly debate.  The problems caused by
excessive paraphyly in classifications was also underestimated during
the middle of the 20th Century, but the excessive pendulum swing toward
strict cladism is far more problematic (even more so than the
vicariance-dispersal pendulum under discussion).  I really hate such
pendulum swings when they go to far in either direction.     
               -----------Ken Kinman              
----------------------------------------------------------      

Jason wrote:
      Please tell me how vicariance is not mentioned, in equal footing,
in this quote. (for those interested the article can be found in this
link
http://elibrary.unm.edu/sora/Auk/v099n03/p0616-p0622.pdf)
 
Michael Heads responded:  
      Of course it is?mentioned. But?Mayr's?center of
origin/dispersal analyses (and Pleistocene vicariance) were?the
standard model for biogeography since the 1940s and for many authors
still are. In the quote above,?Joseph?bemoaned?the effect that
Mayr's work?had had on Australian ornithology, but Mayr's work had?a

similar influence?in many other parts of the world. Whether a
biogeographer was working on the fauna of?Winneba or Wewak, he or
she?was?supposed?to study the?'colonization' of the
area.??Evidently, it was untenable and not worthy of discussion to
think that birds could have been in Australia all along?.