[Taxacom] Biogeography of Australasia

[JF Mate]

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