[Taxacom] Panbiogeography

[John Grehan]

Discussions never achieve more than what they are. This subject is no different.

One can indeed use a panbiogeographic approach for an individual group. One may still be able to identify its main massing, its track, the spatial disposition of taxa on that track, and a geomorphological correlation. All without having a phylogeny. A geomorphological correlation can provide evidence of time. A fossil may falsify that time predication if the fossil is older than that predicted by the tectonic correlation. One may even predict phylogenetic relationships based on the spatial disposition of taxa and then 'test' that against later biological evidence.

But of course in panbiogeography one does not restrict one's world view of biogeographic investigation by single groups, but tries to have some familiarity with biogeography in general. After all, if one does not know what happens in general, how is one to have anything of a perspective on the individual?

Not sure about the 'circularity' argument. 

As for the chance of having a false positive for an individual case, I suppose that is true in general for any method. 

At least you are recognizing that many examples add to the argument and may possibly add up to a correct interpretation. Croizat did argue that biogeography works by 'averages'.

John Grehan


-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Jason Mate
Sent: Monday, May 23, 2011 3:33 PM
To: Taxacom
Subject: [Taxacom] Panbiogeography


John and Michael, we could go on and on about panbiogeographical tit-for-tat, but if wouldn´t achieve much. I can only assume that the problem is that we are looking at different things. Whereas you gather tracks with the idea of figuring out major vicariance events others (lets say me) study particular groups. Panbiogeography doesn´t need phylogenies because it works on large numbers. If you have two areas "joined" by the same tracks you argue that something is going on there, even if many of the tracks are duds. Chances are you are right. However, the problem is when you move from the general to the specific. When you pick one taxon from your dataset you can´t say, specifically, that that taxon´s distribution is predicted by the hypothesis or theory you have postulated. For that specific case you need the phylogeny of the group and fossils to determine if the diversification´s timing is concordant. That is my argument about the circularity of panbiogeography and why you can´t use tectonic evidence to time your taxa.

Best

Jason
 		 	   		  
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