[Taxacom] Dispersal paradigm (was: Antarctic dispersal)

[John Grehan]

Rich,

Ken's position (and I think Jason has a similar outlook, but I may be
confused about that), as outlined in various postings, is that molecular
divergence dates are actual or maximal and so for those cases they falsify
earlier origins and any associated vicariance possibilities. Ken does not
appear willing to accept the reality that fossil calibrated (this is the
most common approach, but island ages are also sometimes used and with
similar problems) ages are minimal estimates only. Ken has asserted several
times that he rejects origins much older than fossil calibrated dates
because he cannot accept them (and that is OK as his personal belief, but
it carries no scientific weight).

John Grehan


On Wed, Jun 18, 2014 at 7:21 PM, Richard Pyle <deepreef at bishopmuseum.org>
wrote:

> Hi Michael,
>
> > You wrote: 'That you can find examples where ecologically
> > disparate organisms fall into repeated patterns of distribution
> > across many different taxonomic groups is not at all surprising
> > to me, because I do not reject vicariance as a mechanism of
> > speciation...'
> >
> > I agree with this, although Ken doesn't - he believes the
> > molecular clock dates and so thinks the geographic patterns
> > are 'pseudopatterns' caused by chance, not vicariance.
>
> I won't speak for Ken, but I have not seen him reject vicariance.  I have
> seen him (usually with good and compelling reason) cast doubt on specific
> cases purported to represent support of vicariance as a contributing
> mechanism to speciation.  I am not familiar enough with the facts in those
> cases to know whether to agree with him or not.  And, if this debate is
> about specific individual cases fitting a pattern or not -- then I think
> that is very much a legitimate debate to have.  But that doesn't strike me
> as the main theme running through this ongoing dialog.
>
> Aloha,
> Rich
>
>
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