More on Biogeographic memory

P.Hovenkamp Hovenkamp at NHN.LEIDENUNIV.NL
Fri Oct 12 10:04:53 CDT 2001


At 04:29 PM 10/11/01 -0400, John Grehan wrote:

>>>I think we've been over this earlier in a thread on biogeographic
>>>homology... My view is that the term homology is inapplicable outside the
>>>context of phylogenetic analysis strictly.
>>>Craw draws heavily on an analogy between phylogenetic and biogeographic
>>>analysis. Granting the analogy, what would be the equivalent of character
>>>analysis? In phylogenetic analysis, the purpose of a character analysis is
>>>to draw up a (putative) character state tree, which is then coded and
>>>inserted in a datamatrix. Would not the equivalent of that be to find a
>>>taxon-tree and use that as basis for the biogeographic analysis?
>
>Since a taxon tree contains no spatial homology information it is not
>biogeographic
>in its own right. The character analysis Craw was referring to is the
>designation of distributions
>as characters and finding those distributions (characters) that are
>homologous (i.e. share the
>same spatial synapomorphy.

No he was not. He was referring to character analysis in "form systematics"
(I take that to mean ordinary systematics, OK?), in order to find an
equivalent in a biogeographic context:

"They are not examples of analytical biogeography
because geographic distribution is taken as read and not subjected to the
equivalent of character analysis in form systematics to determine what
aspects of geographic distributions of taxa are homologies."

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).

>I admit my lack of credentials in graph theory
>so I could be
>wrong about this. If my primitive understanding is correct the character
>analysis has been attempted
>in quantitative terms using connectivity associations between localities as
>proposed, for example, by
>Craw and Page, and nodal analysis such as that by Henderson. I would be the
>first to admit there is
>not a great deal of this kind of analysis for panbiogeography and probably
>that will remain the case
>until some graph theoretician takes further interest.

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

>>>>>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?
>
>No as it is possible for two taxa to partially overlap without sharing the
>same
>baseline. For example, the ratites and Nothofagus overlap, but the former has
>Indian and Atlantic Ocean baselines, the later a Pacific baseline.

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

>>>The main question in my mind is why CGH Panbiogeography offers such a
>>>limited choice of baseline features? Why not let the distribution patterns
>>>speak more for themselves? If several patterns agree on a
>>>Madagascar-Australia relation (e.g., fig. 1-9 A, 3-3, 3-5), - why on earth
>>>"homologize" these with patterns involving India or Borneo (fig. 3-11)?
>
>The baseline offers the hypothesis that the historical origin of all these
>distributions
>is more likely associated with the geographic sector referred to as the
>Indian and/or
>Atlantic Ocean. In this respect the distributions, even though different in
>detail, are
>hypothesized to share more in common regarding their spatiotemporal
>history, than
>with an organism/taxon with a Pacific, or Southern, or Northern baseline.

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?

If it is not a matter of level of detail, my original question remains
unanswered...

>>>That means that according to John Grehan  such explanations are  not "all
>>>that informative at all - let alone 'coherent.'", but nevertheless
>>>explaining the distributions of individual taxa is "a useful enterprise"?
>>>I'm baffled.
>
>No, it means that it is not my opinion that explaining distributions of
>individual
>taxa is not a useful enterprise. To put it the other way (to end confusion
>- sorry I probably
>should have amplified my earlier answer in the first place) it can be
>useful to explain distributions
>of individual taxa - I am agreeing in this respect with Peter Hovenkamp!
Whoopee!
>The point I might
>differ with many bigoeographic practices is the attempt to 'explain'
>individual taxa without some sort of comparative analysis or consideration
>of biogeographic patterns in general.
Whoopee again. I totally agree that explanation of individual taxon
distributions should be based on all relevant evidence.

>>>It must be again an effect of the CGH Panbiogeography book concentrating on
>>>only some parts of Panbiogeography as currently being performed - all the
>>>examples in the book show ocean baselines, with the exception, perhaps, of
>>>fig. 6-12, which shows global biogeographic track relationships based on
>>>Croizat (1958). But then, I may be confused about the difference between a
>>>generalized track and a baseline.
>
>No, I don' think you are confused.
Whoopee!
>And yes, the book does emphasize ocean
>baselines.
>
>>>But Croizat had no problems in drawing different lines across the same
>>>ocean (again, see fig. 6-12).
>
>And neither do we.

For the moment, I'd prefer to continue the discussion about single or
multiple baselines across ocean basins on basis of the remarks I made above.

>>>In contrast, the comparable results of the
>>>CGH analysis (fig. 6-13) show far less detail - with completely
>>>undifferentiated ocean basins.
>
>It is a formalization of ocean basin homology, not a representation of
>track structure.

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.

Peter Hovenkamp

P. Hovenkamp
Nationaal Herbarium Nederland - Leiden
PO Box 9514
2300 RA  Leiden
The Netherlands
hovenkamp at nhn.leidenuniv.nl
http://nhncml.leidenuniv.nl/rhb




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