[Taxacom] Dispersal clarifications: frogs on an oceanic islands

[Michael Heads]

Hi Ken,
 
Back to the start of this thread, the crocodile. Robert Meredith kindly sent me a pdf of their 2011 paper ("evidence for a trans-oceanic voyage..."). As I guessed in my earlier posting, there were two reasons they suggested trans-oceanic dispersal: a paraphyletic basal grade in Africa; and a fossil record of Crocodylus back to the Miocene only. In my view neither of these is evidence for a trans-oceanic voyage, in fact they are both logical errors. The America-Africa clade nested in the African paraphyletic grade is just as compatible with vicariance as with Africa to America dispersal (it involves a break in Africa between the Africa-America clade and its African sister). The fossil age is a minimum only; many groups acknowledged as much older on phylogenetic grounds have a fossil record that only begins in the Neogene. 
 
This is just simple logic and it's not a 'knee-jerk reaction' - I've been thinking about this problem for years.
 
Michael 

Wellington, New Zealand.

My papers on biogeography are at: http://tiny.cc/RiUE0

--- On Tue, 14/6/11, Kenneth Kinman <kennethkinman at webtv.net> wrote:


From: Kenneth Kinman <kennethkinman at webtv.net>
Subject: [Taxacom] Dispersal clarifications: frogs on an oceanic islands
To: taxacom at mailman.nhm.ku.edu
Received: Tuesday, 14 June, 2011, 2:35 PM


Hi David,
      I totally agree. Organisms both disperse and experience vicariant
events as well.  And I would only add the obvious, that not only will
different species have a different balance, but also various higher taxa
will as well.     
       But my experience is that panbiogeographers tend to skew that
balance in favor of vicariance in too many cases.  Panbiogeography sort
of reminds me of strict cladism in that its adherents can tend to go
overboard, although I must quickly add that strict cladism has done far
more damage than panbiogeography ever could.  Not that cladistics (well
done) hasn't done a lot of good, but strict cladism has also done a lot
of harm (far too much of a good thing, so too speak).  Likewise
panbiogeography can sometimes go overboard as well (especially when it
has a knee-jerk reaction against perfectly reasonable dispersal
hypotheses, like Nile crocs founding the American clade).  But the
problems caused by excessive panbiogeography is just a minor nuisance
compared to problems caused by strict cladism during the same time frame
(latter decades of the 20th Century). 
           -----------Ken           
----------------------------------------------------------
David Campbell wrote: 
     "Dispersal" involves multiple factors.  Most mammals are fairly
good locomotors, but many are somewhat large for riding on the average
floating or flying object and the high metabolism limits how long they
can float or swim without food.  Non-swimming mollusks are generally
slow but good at riding and at estivating. Of course, ability to survive
upon arrival is also an issue. 
Organisms disperse and they experience vicariant events.  Different
species will have a different balance.


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