[Taxacom] Biogeography of Australasia

[Ken Kinman]

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.
>