[Taxacom] Biogeography of Australasia

[John Grehan]

Jason,

Thank you for the clarification on the use of the term miraculous. Many
dispersalists have characterized dispersal events as 'mysterious', perhaps
that is a more suitable description.

Still do not understand what you are getting at with the term 'baiting'.
Need to explain if you would.

Historical reconstructions are hypotheses. I am not aware of geological
hypothesis made from geological research necessarily falsify of an
incongruent prediction (hypotheses) made from biogeography. But it is not a
simple case of geology/genes/phylogeny being wrong. In fact, as shown in
Heads' book, it is not a simple matter of geology/genes/phylogeny being
'wrong' but in how they may be interpreted. Panbiogeography looks to
correlation with geomorphology rather than historical hypotheses.
Panbiogeography looks at the spatiality of genes (whether in molecular or
morphogentic form) rather than their interpretation as absolute molecular
clocks based on misrepresenting minimal divergence dates as absolute or
maximal, and looks to the spatiality of phylogeny to examine patterns of
common connections and breaks rather than as imagined centers of origin.
Molecular divergence estimates have been widely hailed as the falsification
of panbiogeography and yet it is the divergence estimate that rested on the
false representation as absolute or maximal dating rather than minimal.

"I acknowledge the fact that successful dispersal over significant barriers
(sea, major ranges) can be an unlikely event on a daily event but over
millions of
years a small probability can really make a impact." In theory perhaps, but
in reality? Panbiogeographic analysis demonstrates that vicariism is
pervasive and patterns of vicariism are shared by "good" and "poor"
dispersers. This makes the theory of chance (extraordinary) dispersal
problematic..

If an organism is said to cross a "barrier" how does one know that it is a
barrier. In panbiogeography the question is less about dispersal and
vicariance being competing mechanisms as they are complimentary.
Biogeographers have traditionally invoked a concept of dispersal (chance,
long distance etc) by which to interpret biogeographic patterns, but
perhaps one could use biogeographic patterns to understand how dispersal
works in the evolution of vicariant distributions.

In summary, you raise questions that have long concerned biogeograhers. I
think you will find Heads' book very informative in this respect and I
would be most interested to see your appraisal of his book in a future
taxacom posting.

John Grehan


On Sat, Mar 22, 2014 at 3:03 PM, JF Mate <aphodiinaemate at gmail.com> wrote:

> Mostly a reply to John but a sprinkling to Michael as well
>
> The use of quotes such as "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 ..."
> suggests that, either by accident or design, you (John) are implying
> dispersal is a mechanism akin to religion. That and the daily readings
> suggest baiting.
>
> As to why congruence of phylogeny and known geological events is
> important (your words):  "...sequence of geological events may
> indicate that the phylogeny predates the geology, is related to a
> different geology, or that the geological reconstruction is wrong."
> John, this makes Panbiogeography unfalsifiable. Your fallback line is
> "geology/genes/phylogeny" could be wrong if they don´t match a purely
> vicariant model. Yes, I am sure that as more evidence acumulates the
> biogeographical scenarios of certain groups will have to change. But
> where panbiogeography fails is in the closed, one size-fits-all
> mechanism department. Science is never "the last word" but the best
> fit to facts. By using this to shield Panbiogeography you are
> purposefully using scientific uncertainty to protect your ideas.
>
> As to "The significance of observed cases of dispersal of highly
> vagile species as evidence of chance dispersal being a significant
> force in biogeography is questionable and does not predict the
> tectonic correlations between good and poor dispersers (in the sense
> of means of dispersal)." There are plenty of examples of species
> (mostly good flyers) which have crossed significant barriers (even
> oceans) and colonized new areas in recent history. How are these
> examples not appropriate to the discussion? As for successful
> colonization, just look at gardeners in Europe or NA. Thousands of
> introduced, carefully nurtured plants, often cultured for generations
> and only a small fraction ever becomes naturalized. I acknowledge the
> fact that successful dispersal over significant barriers (sea, major
> ranges) can be an unlikely event on a daily event but over millions of
> years a small probability can really make a impact. The mechanism is
> certainly common enough to suggest it does not require divine
> intervention to happen.
>
> "Similarly, repopulation does not substanciate chance dispersal as a
> significant force in the sense of chance dispersal being a major
> mechanism in biogeography." and Michael "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."
>
> This is a play on words. There is no valid/clear-cut distinction
> between "chance dispersal", "range extension" or your "dispersal" vs
> the meaning of the word as used by most biologists. I understand that
> panbiogeography requires this (non-existant) difference to distinguish
> itself, but in the end you only need a few observed cases of organisms
> crossing barriers to show that, given the right conditions, dispersal
> is a valid mechanism. Maybe not 99% of the time, but chance plays a
> bigger part in evolution than 0, and that is what matters.
>
> Best
>
> Jason
>
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