[Taxacom] Biogeography of Australasia

Sat Mar 22 02:04:47 CDT 2014

Hi Jason,
No-one is arguing that dispersal is a significant force. All organisms have
dispersed to their current locations. Dispersal can be observed every day.
Vicariance biogeography has never denied dispersal - you can't just have
vicariance otherwise there would only be a single taxon in any area.
Michael Heads

On Sat, Mar 22, 2014 at 2:50 AM, JF Mate <aphodiinaemate at gmail.com> wrote:

> John you have been baiting and Ken bit, and naive me, I too will
> follow. I think that the choice of words (miraculous?) speaks volumes
> as to the impossibility of discussing panbiogeography in a logical
> fashion. As for believing, well, we take leaps of faith, possibly not
> based on the best of evidence. Having said that, the repopulation of
> islands after devastation or the observed cases of dispersal of highly
> vagile species, together with phylogenitic patterns which are
> incongruent with the timing or sequence of geological events are,
> IMHO, sufficient to make dispersal a significant force in
> biogeography.
>
>
> Best
> Jason
>
> On 21 March 2014 12:04, John Grehan <calabar.john at gmail.com> wrote:
> > Ken,
> >
> > It was Darwin who invoked the concept of miracles for anyone denouncing
> his
> > theory of centers of origin and dispersal.  You are welcome to believe in
> > extraordinary events as the basis of biogeography and evolution, but the
> > point is that such an approach calls upon 'miraculous' events to explain
> > patterns when such events are not even necessary.
> >
> > Explain away what 'survivors'. What you 'suspect' is uninformative.
> Better
> > to read the book and then make assertions. . The 'superiority of
> > panbiogeography , as I see it, is that it relies on the empirical facts
> of
> > distribution, not to which area of the world it is applied since it is
> > applied to all areas, as you will see in Heads' book if you take the time
> > to read it.
> >
> > If there is no doubt many such cases of tracks and dispersals (this does
> > not actually make any sense) this would have been demonstrated, but it
> has
> > not.
> >
> > Caecillians are neither here nor there when it comes to biogeography
> since
> > 'good dispersers' and 'poor dispersers' show the same tectonic
> > correlations. In this context caecillians are no better or worse a
> > demonstration of vicariance than any other group..
> >
> >
> > John Grehan
> >
> >
> > On Thu, Mar 20, 2014 at 10:23 PM, Ken Kinman <kinman at hotmail.com> wrote:
> >
> >>  Hi John,
> >>           I don't think extraordinary events only happen once in tens of
> >> millions of years.  Depending on the ability of an organism to disperse
> >> across "large" distances, some such events could easily occur on the
> order
> >> of thousands of years (not millions), but either way most simply fail to
> >> become well-established where they happen to land (whether that
> dispersal
> >> was by ocean currents, wind, on rafts of vegetation, or on the bodies of
> >> vagrant animals, such as seeds or parasites).  Even those which do
> become
> >> well-established would admittedly be "difficult to investigate or test",
> >> but that certainly doesn't warrant your commentary that such
> >> extraordinary events in evolutionary history should be compared with
> >> miracles (a religious concept).
> >>
> >>       And Australia's long history of geographic isolation in particular
> >> makes it a very poor candidate for documenting cases of dispersal
> >> survivors, but I suspect panbiogeographers are inclined to explain away
> >> such survivors in favor of a non-dispersal explanation.  So I am not
> >> surprised that chance dispersal was not "necessarily" invoked in this
> book
> >> on a very isolated part of the world.  A similar book on the biota of
> >> Madagascar might be a better test of how superior panbiogeography might
> be
> >> to other approaches.
> >>
> >>                  ---------------------------Ken
> >>
> >> P.S.  And by the way, there are no doubt many cases where it is
> actually a
> >> combination of panbiogeographic "tracks" and dispersals that are the
> best
> >> explanation (geographic factors constraining most dispersals to such
> >> "tracks").  Why does it necessarily have to be just one or the other?
> >>  Perhaps you are just too prone to explain such "tracks" by vicariance
> >> rather than by constrained dispersal routes.  There could well be a
> >> continuum from very rare dispersals (on the order of millions of years)
> to
> >> more frequent dispersals (between a thousand and a million years).  So
> much
> >> time during which many extraordinary events could occur.   I see no use
> in
> >> branding any of them with a loaded term like "miracle".   Not that
> >> vicariance should be dismissed either, especially in organisms like
> >> caecilians that have very low dispersal potential----but one family of
> >> caecilians apparently hitched a ride as India drifted from Africa to
> Asia.
> >>  Probably one of the best cases of continental drift and vicariance
> >>  explaining geographically separated taxa.   So I am certainly not
> >> anti-vicariance.
> >>
> >>
> >>
> ------------------------------------------------------------------------------------------------------------------------------------------------------------
> >> John Grehan quoted and then commented:
> >>
> >> > P 12 "The fourth process, speciation by founder dispersal, is
> >> > controversial. It explains geographic distribution by chance -
> >>
> >> > extraordinary events that are proposed to happen only once in tens of
> >> > millions of years...Chance dispersal events do not correlate with any
> >> other
> >> > physical or biological factor and can explain any distribution, but
> they
> >> > are also difficult to investigate or test. Chance dispersal may occur,
> >> but
> >> > it has not been necessary to invoke it for any of the Australasian
> >> > distributions examined in this book."
> >> >
> >> > Mike's previous book has been criticized by molecular dispersalists
> for
> >> > using vicariance, and yet, as is pointed out above, it is not even
> >> > necessary to invoke chance dispersal through extraordinary events. To
> >> > invert Darwin's (1859) appealing to the extraordinary is akin to
> >> appealing
> >> > to miracles.
> >> >
> >>
> >>
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>
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-- 
Dunedin, New Zealand.

My recent books:

*Molecular panbiogeography of the tropics.* 2012. University of California
Press, Berkeley. www.ucpress.edu/book.php?isbn=9780520271968

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