More on Biogeographic memory

John Grehan jrg13 at PSU.EDU
Fri Oct 12 08:35:28 CDT 2001


>So my question still stands: character analysis is about character states
>and character state trees, and why is the equivalent in biogeography not
>about taxa and taxon trees?
>(I wish I could think of a proper equivalent in character analysis of the
>CGH Panbiogeographic concept of spatial synapomorphy - perhaps after the
>weekend).

On this I guess we take different interpretations. At present I stay with
the view that form systematics includes designation of informative
characters by synapomorphy and it is designation of a biogeographic
synapmorphy to which Craw was referring. While I believe I am correct in
this understanding, I do not understand Hovenkamp's view that the
biogeographic 'equivalent' of character analysis in form systematics is
'taxa and taxon trees' since that is not an equivalent of form systematics,
that is form systematics itself.

>This is not graph theory. It is about the conceptual relation of homology
>and phylogeny.

On this we are in disagreement.


>Of course. But to be examples of the same common pattern they have to
>comply with *both* requirements. The ratites and Nothofagus don't.

If one is referring to 'same common pattern' as a common baseline the
answer would be no as there can be two different distributions that do not
overlap at all and share a common baseline since both tracks cross the same
diagnostic feature.

>So it seems to be a matter of the level of detail of the analysis. In a
>more detailed analysis of the Indian Ocean basin, CGH Panbiogeography may
>consider different baselines across different parts of it?
>
>If that is so, it raises the question on what grounds CGH Panbiogeography
>is able to decide in advance of the analysis that there is a part-whole
>relationship between these different parts and the whole Indian Ocean?
>After all - that is not trivial. An alternative would be that there is a
>part-whole relationship between the southern half of the Indian Ocean and
>the "Southern Basin". In which case the designation of the
>Madagascar-Australia track as Indian Ocean baseline should be changed.
>Somehow, for some reason, CGH Panbiogeography has already opted for the
>first option, but has it seriously considered the alternative? If so, on
>what grounds has it been rejected?

There is always the possibility that there may be disagreement about the
designation of baselines, but to do so one would have to accept the
validity of baseline homology otherwise the question is pointless (for
example I would not bother to decide among two competing Darwinian center
of origin hypotheses). If one decided to critique and offer alternative
baseline designations that is fine with me - I would naturally encourage
the activity. Certainly there are examples of more detailed considerations
of baselines such as Craw's (1989) comparison of baselines with respect to
the Chatham Islands.

Designation of different trans-Ocean baselines is certainly a possibility.
I would conceive, for example, the designation of distinct tectonic
features within an ocean basin providing different terms of spatial reference.

On the face of the evidence a Madagascar-Australia baseline is simply
referring to the distribution crossing the Indian Ocean. Its origin with
respect to ocean basins and tectonics not crossed by the track may be
subject to speculative consideration, particularly if a related group, for
example, did have another baseline. The historical interrelationship of the
two would be an issue of potential interest.


>Whoopee again. I totally agree that explanation of individual taxon
>distributions should be based on all relevant evidence.

Except spatial evidence through baseline homology apparently does not
constitute evidence at all in your view.

>Excuse me for thinking otherwise. The caption says:
>"Formalized panbiogeographic classification of major biogeographic regions
>as ocean basins". I did not interprete the clause "as ocean basins"
>correctly as being restrictive instead of amplificative.

And I concede that there may always be better ways to represent the
panbiogeography of Croizat. Naturally the 'CGH' book represents a level of
relative agreement about panbiogeography by those authors. Others may take
different panbiogeographic emphasis (e.g. some of the works Morrone and
others in Latin America), and even we three collectively may have different
perspectives and emphasis in our work. In form systematics there is a very
large number (relatively) of theorists involved and a matching diversity of
thought on the right or best systematic approach). Its just a matter of
history that we pioneered the exploration of panbiogeography. It could have
been Nelson et al, except they chose to subsume panbiogeography under form
systematics.

John




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