[Taxacom] Panbiogeography

[JF Mate]

John, sorry for the delay in replying.

"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."

Your priors are limited to tectonics. Ergo, everything to you looks
like a nail so your interpretations are limited to the scenarios you
are willing to contemplate. It's like living in Flatland, you only see
some dimensions.


"Panbiogeography looks to correlation with geomorphology rather than
historical hypotheses."

Biogeography in general looks at the correlation between distribution
patterns, phylogeny and then looks for mechanisms to account for this,
geology and dispersal. Thus it is not the sole domain of
pnabiogeography. The difference is that Panbiogeography does not
contemplate dispersal because, me thinks, that would make the results
fuzzier and therefore would make it impossible to justify the
tautology that in the bottom it has become: biogeography predicting
geology and viceversa.

"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."

Ken has already told you that your desire to stretch maximal dates to
fit (no, shoehorn) your only contemplated mechanism (tectonics) would
often lead to ridiculous scenarios. Phylogeny calibration is as good
as the calibrating points so it is work in progress, but rather useful
when comparing relative timings within the phylogeny. Thus, it is very
likely that many lineages will, in time, be shown to be older than
initially estimated. However it is mystifying to me how it can be used
it to justify their position. We can only talk of the data that we
have, not the data that can possibly exist. Thus Panbiogeography asks
for the impossible, that other biogeographers prove that a fossil does
not exist. This is what I mean, in part, about Panbiogeography being
unfalsifiable.


"Panbiogeographic analysis demonstrates that vicariism is
pervasive..." No, panbiogeographic analysis is a hammer and only sees
nails.But when you find a screw you insist it must be a nail.
Vicariance is common, that's all.

"... and patterns of vicariism are shared by "good" and "poor" dispersers."
How do you define good an bad disperser if, according to you, they do
not exist? In any case, what is the significance of your statement? We
are talking about succesful dispersal, which is random and likely a
combination of factors.

"This makes the theory of chance (extraordinary) dispersal
problematic." Are you seeking some sort of meaning in nature? As to
equating chance and extraordinary as equal, playing
dice is a game of pure chance but not extraordinary. It is the
combination of probabilities that would make it highly unlikely
(extraordinary). Successful dispersal becomes more unlikely with
increasing distance, the degree of tapering of which is likely
taxon-specific. So unlikely yes, but extraordinary is a choice of
words as poor as "miraculous" or "mystifying".

"If an organism is said to cross a "barrier" how does one know that it
is a barrier."
Normally, something like this: if it dies there with a certainty of a
100%, it is a barrier, if survival is equivalent to its normal
habitat, it is not and in between you have a fuzzy area. I guess that
is why Stephen thinks dispersal is more relevant in the pacific
islands (more tightly defined 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,..."
They have invoked dispersal as one of the mechanisms to explain biotic
distribution.

"...but perhaps one could use biogeographic patterns to understand how
dispersal works in the evolution of vicariant distributions."
So we assume dispersal does not exist so we can use vicariance to
understand how dispersal works... even though it doesn´t exist? You
need to explain this a bit.


Michael

"The difference between normal, observed dispersal discussed by
ecologists (e.g. weeds dispersing into a garden), and chance, 'jump'
or 'long distance' dispersal as invoked by evolutionists, is that the
former does not involve differentiation, whereas the latter is
proposed as a mode of speciation."

Not true and no different (except in scale that is). We may argue
about the actual probability the range of dispersal, but dispersal is
a probability curve with a long tapering tail with increasing
distance. Also dispersal is but one mechanism leading to allopatry
(Mayr or Dobzhansky mention "barriers" emerging as well).

"Dispersal theory explains range overlap by dispersal, but also
explains allopatry by dispersal. Vicariance theory explains range
overlap by dispersal, but explains allopatry by vicariance."
Dispersal is one mechanism to explain allopatry. Vicariance in
Panbiogeography is the only mechanism contemplated for reasons that
have been explained many times before by people far abler than me.


"Note that the dispersal invoked in vicariance theory is caused by
geological change, whereas dispersal as invoked by dispersal theory to
explain allopatry, is caused by chance."
So you think chance is somehow wrong? You need to elaborate.