[Taxacom] Dispersal paradigm (was: Antarctic dispersal)

Wed Jun 25 01:18:45 CDT 2014

Hi Jason,

You wrote: ''I believe you are confounding dating the object with dating
the biological significance
of the event'.

No, they are obviously different, and I'm arguing that the age of the
object (fossil) is very different
from the age of its clade. Fossils are often very accurately dated; the
problem is the clade age.

You wrote: 'rifting continents and rising mountains have a beginning and an
end'. No-one is
arguing with that. The point is that the events (their beginning and end)
are often very accurately
dated with radiometric techniques. Also, the delimitation of the clades and
their geographic
distributions are now often very well supported in molecular studies. (In
contrast, the fossil-based
clade dates are very problematic)  Why not use these results to date a
large number of clades
and see what happens? Does it lead to a coherent synthesis or does it go
nowhere, with contradictory
conclusions? Instead of testing the approach, the orthodox line is to
compare it with creationism
and call for it to be banned (Waters et al., 2013 Syst Biol 62: 494). Would
you support testing
or banning?

You wrote: 'As Richard rightly pointed out, so many taxa and so few
patterns'. No. I'm the one
supporting few patterns. (Richard said: 'By using the word "generality",
are you
implying that *most* (nearly all?) species of life on earth are members of
these groups with
repeated patterns of distribution?  If so, then one would surmise that
there are a finite set of
patterns, and the vast majority of species fall into one of these group
patterns.  That's certainly
not what I see on coral reefs').

I asked the question, just how much older is a clade than its oldest
fossil? You wrote: 'Asking
me to give you a hard rule of thumb for fossils is pointless because it
would depend on each
case'.  OK, how about an estimate for any group? You seem to disagree with
the view that
there is a fundamental problem here (termed 'the problem of the priors' by
recent authors) - is that
right?

You wrote: 'Timing is the key and the circularity of your method makes it
impossible to
determine without resorting to circularity'.

How is the method circular? The use of vicariance events to provide dates
is based on a
simple deduction: if the phylogenetic break was caused by a spatially
coincident tectonic feature,
and this is dated at *x* million years old, then the phylogenetic break is
also *x* million years old;
there is no circular reasoning here, whether or not particular cases of
tectonic-vicariance
calibration are incorrect. If a model of vicariance caused by tectonics is
adopted, deductions
about the age of a break can be tested against each other and other events.
This follows a
normal process of investigation based on the proposal of hypotheses,
testing of predictions
deduced from the hypotheses, and the framing of new hypotheses.

On Wed, Jun 25, 2014 at 5:33 PM, JF Mate <aphodiinaemate at gmail.com> wrote:

> 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
> >>
> >>
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> >>
> >> Celebrating 27 years of Taxacom in 2014.
> >>
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> >
> > Celebrating 27 years of Taxacom in 2014.
>
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> Celebrating 27 years of Taxacom in 2014.
>

-- 
Dunedin, New Zealand.

My recent books:

*Molecular panbiogeography of the tropics.* 2012. University of California
Press, Berkeley. www.ucpress.edu/book.php?isbn—80520271968

*Biogeography of Australasia:  A molecular analysis*. 2014. Cambridge
University Press, Cambridge. www.cambridge.org/9781107041028