[Taxacom] Hedges /Kumar (eds) The Timetree of Life

[John Grehan]

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu
[mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Sergio Vargas
 
> but in addition it can function in the absence of dispersal (or >
explain it away). 

Panbiogeographic methodology does not assume dispersal or vicariance. 

> Surely organisms can move around and sometimes hit the insular 
> or contienetal jackpot. 

Surely

> Calling names like dispersalists seems to me like a tactic to 
> draw attention away from the limitations of the 
> panbiogeographical methodology.

No, its used in reference to those who regard centers of origin and
means of dispersal as an empirical foundation for biogeographic
analysis. 

> I agree with you that cladistic biogeography recognizes both 
> dispersal and vicariance, it uses vicariance as a null model and
>  when the null model doesn't fit postulate dispersal (pre- or
> post- speciation) to explain discordance. 

The trouble with cladistic biogeography' (I put that in quotes as there
are various renditions) is that without panbiogeographic techniques it
cannot assign geographic homologies.

> Now, panbiogeography can use phylogeny as well. Page published a
>  method to incorporate phylogenetic information into track 
> construction. To the best of my knowledge, this method has been
> never used. 

Which information specifically?


> This I think is because people tend to use panbiogeography as an
> escape when they don't have phylogenies at hand. 

This is bizarre beyond belief. This would get a zero on an exam
question.

> But yes, it can work without a reference phylogeny for the group of
organisms under study. 

Again bizarre stuff. Obviously never even read Craw et al (1999).

> Regarding dispersal, I disagree with what you say about 
> panbiogeography working without dispersal or explaining 
> dispersal away. Criozat term mobilism clearly refers to 
> dispersal, but definitely not to random dispersal. 

It does not matter whether its random or not. 

> I think, panbiogeography tries to look for the causes of 
> "inmobilism", hence panbiogeography's fixation with vicariance. 

You 'think'?

> I think the core of the controversy between panbiogeographers 
> and dispersalists is that the panbiogeography rejects random 
> dispersal as an explanation for distribution patterns. 

If one read dispersalist theory one usually finds that the underlying
dispersalist objection lies in a rejection of spatial information in
biogeographic analysis. Anything else is ok - whether it be fossils,
molecular divergence dates, belief in means of dispersal or centers of
origin. Anything at all, as long as it is not geography.

> There is another problem 

Another problem? Oh goody.

> with panbiogeography in its current incarnation. This has 
> nothing to do with Croizat or the way he did his panbiogeography
> but with the use of clique analysis for the determination of 
> generalized tracks. If you check Croizat's work (not an easy 
> task: hard to read and to follow), it is clear that he operated
> with graphs summarizing the distribution of a taxon. Yet, track 
> compatibility analysis operates on a compatibility matrix, and 
> no longer on the graphs. Moreover the graphs are never used if
> you use this approach because when you code the individual 
> tracks for compatibility analysis you loose all the information
> on the edges of the graph. 

Since when is clique analysis the only panbiogeographic method?

> I could be completely wrong though... would not be the last one
> not understanding Croizat's writings ;-)

It does not matter really as it is likely that no one ever understands
everything.

John Grehan

cheers

sergio