[Taxacom] Dispersal... again

[Michael Heads]

Hi Ken,
?
My responses are below.
?
Michael

Wellington, New Zealand.


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


________________________________

From: Kenneth Kinman <kennethkinman at webtv.net>
To: taxacom at mailman.nhm.ku.edu
Sent: Monday, 31 October 2011 7:39 AM
Subject: Re: [Taxacom] Dispersal... again


Michael,
? ? ? I was a bit surprised by what you wrote below.? Just "ditching"
the center of origin/dispersal paradigm and replacing it with vicariance
is extremely one-sided and short-sighted.? 

MH:?Why do you think that? Any relevant data or ideas?

Mayr's "pluralism" in biological explanation is more even-handed, 

MH: Mayr did not accept pre-Pleistocene vicariance - that is not?pluralism.?

even if he found more
evidence for dispersal than vicariance (not surprising since birds are
so mobile). 

MH: There is no more evidence for chance dispersal/center of origin in birds 
than any other group. If they really were as mobile as they appear to be, there 
wouldn't be any areas of endemism. They have potential mobilism but in 
practice they stick to their area very closely.?
?? In your last letter you wrote: '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)'.??????????? 
I asked for a reference to this,?but you didn't reply.

???? That's one reason why he refered to dispersals as "primary"
discontinuities and vicariance as "secondary" discontinuities.? Another
reason is that it makes sense that a species has to disperse to increase
its range (a primary event) before it can become subject to secondary
events (like vicariance).? 

MH: Not necessarily. If a widespread American group differentiates into a North 
American species and a South American species, these are both widespread but 
have not spread out from a center of origin. (The origin of the initial, widespread 
American group is another question. It may have also originated by vicariance, 
e.g. with an African group).?Widespread species may not have?spread at all, but 
could have evolved in situ.?('Pluralists' will always reject this). Of course, this 
does not deny that species *may* undergo subsequent range expansion, but many 
will not.??

Your "mirror" analogy makes no more sense to
me than it does to Jason, except perhaps in a small minority of cases.

MH: It doesn't make sense to?pluralists because?you?don't accept simple 
vicariance. But many authors now do accept it.

It does not reflect the kind of paradigm that would have broad
applicability, 

MH: The mirror analogy was borrowed from Chakrabarty's?excellent review 
of cichlid biogeography (Fish and Fisheries 5: 97. 2004).?Authors on countless 
other groups now invoke?pre-Pleistocene vicariance.?

especially by "ditching" the idea of centers of origin
outright.
??????? If you place too much faith in vicariance alone, 

MH: Vicariance alone obviously wouldn't?work - you would end up with 
every small area having just one?(endemic) clade. I've?suggested?that phases 
of vicariance alternate with phases of geographic overlap by range expansion. 
This?can lead to the piling up of diversity in particular areas.

you are
shutting yourself off from the wide variety of ways nature has had of
increasing its biological diversity.? Mayr practiced pluralism, 

MH: No, in his?analyses?everything was center of origin. Look at his classic 
analysis of the North American bird fauna, for example - he?tried to trace the 
center of origin of every group. No vicariance. His analysis of the tepui bird 
fauna: the same. His analysis of the Solomons/Bismarcks bird fauna: the same.

even if he did not embrace vicariance as much as you might like.

MH: He didn't embrace pre-Pleistocene vicariance at all.

? I don't know
about Hooker's or Huxley's views of speciation, so can't judge if they
were as one-sided as you suggest (largely "ditching" centers of origin
and dispersal).? 

MH: Here's a typical quote from Hooker (1860). The
Australian flora, ?though 
manifestly more allied to the Indian [s.lat.] than to any
other, differs from it so 
organically, that it is impossible to look upon one
as derived from the other, 
though both may have had a common parentage.? He finds the 
center of origin/dispersal model 'impossible'.

????? However, I'm certainly not going be like Gaylord Simpson and
suggest that vicarianists (like Croizat) write from insane asylums, but
if they are that one-sided, perhaps I should be like Mayr and simply
ignore them.? 

MH: Yes, that was his?pluralist approach.

As I said before, these threads don't seem to be getting
anywhere.? 

MH: Jason suggested the same thing about the thread, but one offlist correspondent 
(not John Grehan) responded: 'It's actually extremely useful, both as to content 
and the  importance of attitudinal matters in science'.

Banging my head on this brick wall is really giving me a
headache, so I guess I should take a clue from Mayr and just ignore the
wall (which doesn't mean ignoring vicariance, but just vicariance in
excess---all things in moderation is the best policy).? ? ?

MH: So you would accept the?Ptolemaic geocentric system, the Hippocratic humors, 
the phlogiston theory, spontaneous generation etc., all in the name?of pluralism? 
What about sceptical rationalism?
?
???????
??????????? ----------Ken? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 
----------------------------------------------------------? 

Michael Heads wrote:? 
? ?  It doesn't really have anything to do with plate tectonics, it's
the center of origin/dispersal model for speciation that's the problem.
Hooker and Huxley didn't know about plate tectonics, but they made very
important?progress in biogeography. This was?because, to a large
extent, they ditched the center of origin/dispersal paradigm and
accepted vicariance, not?movement,?as the model for speciation.? 
???? 



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