[Taxacom] No more whingeing?

Kenneth Kinman kennethkinman at webtv.net
Wed Feb 1 22:35:45 CST 2012


Hi Karl,
       I would tend to agree in general with your point below regarding
panbiogeographer's mindset.   However, an even more fundamental problem
(in my view) is that their broader arguments often tend to rest on a
false dichotomy of vicariance versus dispersal----as if "never the twain
shall meet."  In a majority of cases, a combination of vicariance and
dispersal probably provides the best answer, but the dispersal component
is often disparaged by extreme panbiogeographers (exemplified by John
Grehan in particular).
   
      Even Michael Heads (who seems less extreme in this regard) seems
overly influenced by vicariance and overly critical of dispersalist
hypotheses in a lot of cases.   In particular, note his arguments in the
paragraph "Origin of the ancestor".  It seems to repeat the excessively
anti-disperalist notion that you can repeatedly shatter a widespread
species (like a mirror) into vicariant subtaxa, and that this somehow
obviates the need to consider dispersal as having created such
widespread populations in the first place.  Michael Heads' view on this
point is hard enough to swallow (much less John Grehan's seemingly more
extreme extrapolation of the "shards of a mirror" argument to an absurd
degree.   

     Such arguments are based on a false dichotomy and thus remind me
more of a political campaign than a scientific debate.  My view is that
panbiogeographers (some more so than others) tend to be so
anti-disperalist that they become excessively pro-vicariance.  In most
cases, I am convinced that the answer is most often somewhere in between
what either extreme dispersalists or extreme panbiogeographers might
argue.         

       I have no doubt that this new book will have some fine
pro-vicariance examples and arguments, but having read what was written
under "Origin of the ancestor", I also expect there will be examples and
arguments that are overly anti-disperalist as well.  It is just a matter
of separating the wheat from the chaff, and my experience with
panbiogeographers is that they often tend to generate just as much chaff
as many of the dispersalists they criticize (some more so than others).         
         ---------------Ken Kinman   
          
-------------------------------------------------------------
Karl wrote:  
        Not really.  The Chapter 1 excerpt makes it clear (in the
section "Island biogeography with metapopulations and without founders")
that Heads' case rests on including plant dispersal among oceanic
islands separated by hundreds of miles under his category of "ordinary
movement, seen every day".  Somehow, in panbiogeographers' minds, events
that happen every few thousand years can't happen over longer distances
every few tens or hundreds of thousand years. 







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