[Taxacom] Dispersal paradigm (was: Antarctic dispersal)

[JF Mate]

Michael sorry for the tardy reply but I am travelling quite a bit.
Going back to your email, I believe you are confounding dating the
object with dating the biological significance of the event. Fossils
can also be very accurately dated, but that is not the problem. What I
am simply stating is that rifting continents and rising mountains have
a beginning and an end, or at least a range from the earliest
inception to when they can be considered actual barriers. And just
because something starts it doesn?t translate into an outright
splitting of all taxa. Case in point the Red Sea or the East African
rift. Even when you have a proto-sea in between, how far would you say
it need be to split all biota?

In the end you also have to make an educated guess. Asking me to give
you a hard rule of thumb for fossils is pointless because it would
depend on each case. I would argue however that with ever more fossil
coverage uncertainty will be minimized. This is preferable to ad hoc
timing of any pattern that can be fit on to tectonics. As Richard
rightly pointed out, so many taxa and so few patterns. Timing is the
key and the circularity of your method makes it impossible to
determine without resorting to circularity.

John, I challenge you to find any statement where I deny vicariance as
a major mechanism in biogeography. Or that molecular divergences are
actual. Or that any fossil can be perfectly assigned within a
phylogeny. My position is that they are all estimates, including
tectonic-based calibrations.

Best

Jason

On 19 June 2014 01:47, John Grehan <calabar.john at gmail.com> wrote:
> 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
>>
>>
>> _______________________________________________
>> Taxacom Mailing List
>> Taxacom at mailman.nhm.ku.edu
>> http://mailman.nhm.ku.edu/mailman/listinfo/taxacom
>> The Taxacom Archive back to 1992 may be searched at:
>> http://taxacom.markmail.org
>>
>> Celebrating 27 years of Taxacom in 2014.
>>
> _______________________________________________
> Taxacom Mailing List
> Taxacom at mailman.nhm.ku.edu
> http://mailman.nhm.ku.edu/mailman/listinfo/taxacom
> The Taxacom Archive back to 1992 may be searched at: http://taxacom.markmail.org
>
> Celebrating 27 years of Taxacom in 2014.