More on Biogeographic memory

P.Hovenkamp Hovenkamp at NHN.LEIDENUNIV.NL
Tue Oct 9 16:14:33 CDT 2001

I am afraid much of this discussion is now starting to run in circles. For
once, I'll start deleting parts of the message while replying to other parts.

At 09:02 AM 10/9/01 -0400, John Grehan wrote:
>>Then why the remark that "vicariance biogeography seems to simply be a
>>version of Darwinian biogeography" you made earlier?
>Because most, if not all, applications of vicariance biogeography utilize
>the Darwinian concepts of centers of origin and dispersal (with vicariance
>simply being part of this framework as correctly pointed out by Mayr) and
>utilize Darwinian concepts of spatial structure (such as areas of endemism
>as natural units of biogeographic classification) and homology.

This discussion started with a statement by me that Vicariance biogeography
at least *tried* to consider biogeography as independent from geology. What
most, if not all applications currently *do*  is another thing.

>>Agreed. In vicariance biogeography (and in panbiogeography as well) we can
>>observe commonality in geographic overlap
>Except the homology criteria for each is different. Homology in
>panbiogeography is a spatial character.

There is not necessarily a concept of homology in vicariance biogeography.
The application of the term "homology" to matters biogeographical is purely
restricted to CGH Panbiogeography.
Accepting this usage, then, in vicariance biogeography we can observe
commonality when distributions (partly) overlap, in CGH Panbiogeography
when they overlap _and_ share the same baseline. Is that it?

>>Grehan's "Darwinian biogeography" seems to be virtually synonymous with
>>"Taxon history", and thus does not aim at making novel predictions about
>>geology. T
>I agree with Hovenkamp on the inability of Darwinian bigoeography to inform
>about geology. I don't see any such Darwinian "taxon history" being all
>that informative at all - let alone 'coherent.'
>>he criticism is invalid. It may be John Grehan's view that
>>explaining the distributions of individual taxa is not a useful enterprise
>No it is not.

Not your opinion, or not a useful enterprise?

>>It would also run counter to the general trend in the CGH
>>Panbiogeography-book, where most examples (and many of Croizat's examples
>>also) are concerned not with finding common patterns (generalized tracks)
>>but with explaining single distribution patterns.
>So panbigoeography can accomodate both "earth history" and "taxon history"
>in Hovenkamps dichotomy.

Failing a method to assess commonality independently from geology, just
"taxon history", I'm afraid.

>>But which I applied deliberately - I see no better term to describe the way
>>in which different biological patterns are assigned the same baseline
>>(examples cited in earlier posts).
>Forcing implies no necessary methodological relationship whereas there is a
>methodological requirement for baseline assignment. However, if one defines
>'forcing' as necessary assignment then I would agree just as one may
>'force' a character to be a synapomorphy by virtue of it conforming to the
>crtirion of synapomorphy.

I may have difficulties in defining "forcing", but I apply the term because
(as has been established in earlier posts), CGH Panbiogeography accepts
only 5 different types of trans-oceanic baselines (corresponding to the
major ocean basins), thus forcing all possible transoceanic patterns in
only 5 pigeonholes.

>>This makes the distinction one of degree: CGH Panbiogeography simple makes
>>use of less detailed geological data.
>No, the difference is Darwinian biogeography simply taylors biogeographic
>'explanation' onto selected geological narratives about the past, whereas
>panbiogeography assigns baseline relationships with respect to geological,
>geomorphological, tectonic structures to generate a homology link between
>biology and geology. For panbiogeography the geology can be as detailed as

Sorry - when I said less detailed geological data, I meant data that did
not contain any historical information.  That seems to be undisputed.

>  I get the impression that Hovenkamp views the panbiogeography
>book as the be all and end all of post-Croizat panbiogeography.

I had expected it to be an up-to-date review of the whole field, yes.

>>>>So there is
>>>>*no* independence.
>>>There is independence of method with respect to constructing tracks, nodes,
>>>and main massings.
>>Baselines significantly left out here. Q.E.D.
>Obviously it is necessary to make a methodological connection with earth
>history or biogeography has no necessary relationship with earth history
>hypotheses other than speculation in light of current knowledge. The
>baseline provides that link. The independence of panbiogeography is
>independence of its methodology - including baselines - from hypotheses of
>geological history. By having a pattern connection with geology Croizat was
>able to use baselines to generate novel geological predictions -
>predictions that have since received independent geological corroboration.

Croizat's writings cover several thousands of pages - it would be a
statistical miracle if it was *all* wrong ;-)

Seriously - what strikes me when reading Croizat is the stubborn refusal to
accept current maps as relevant for the explanation of distribution
patterns. A world of difference with the straitjacket of (current) ocean
basins imposed on biogeographical data in CGH Panbiogeography.

>>Making John Grehan's claim that "Panbiogeography can incorporate as much
>>detail that resolved (biological) phylogenies provide in track
>>construction" a rather unsubstantiated one.
>No it does not. It simply means that the book was not focused on details of
>phylogeny. It is obvious that one may draw tracks for any phylogeny. The
>more detailed the phylogeny the more track connections between related taxa
>one may draw. Simple as that.

And the references?

P. Hovenkamp
Nationaal Herbarium Nederland - Leiden
PO Box 9514
2300 RA  Leiden
The Netherlands
hovenkamp at

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