More on Biogeographic memory

John R. Grehan jrg13 at PSU.EDU
Mon Oct 15 14:06:49 CDT 2001


>This is likely the case, hence my insistance for explicitation.

Agreed, but just for clarity - the use of the baseline as an implicit
operational procedure has been the case for non-panbiogeographers, even
those who have opposed panbiogeography.

>The puzzling question remains: what is the historical signification of this
>"pattern of spatial relationships"? How do we interpret it (historically),
>and why?
>What are "spatial homology" and "spatial synapomorphy" or "spatial
>correlation", and do they what mean? I guess I know what they are (shortest
>spatial distances some way). But what do you consider they mean, and why?

These are natural enough questions and while not everyone may agree on the
answers, the issues are  covered in the panbiogeographic literature



>>So far it [panbiogeography] has been very successful indeed in
>>mapping the global structure of biogeography with its successful
>>(corroborated) geological predictions and even some biological predictions.
>
>Specifying these "predictions" could perhaps help answering the questions
>above (meaning of a spatial "homology"?).

The predictions are specified in several publications including the
panbiogeography book. The composite geological structure of the Americas is
one example. Prediction of Ficus relationships is another.


>>Further developments in spatial analysis for historical biogeography would
>>be very welcome. I have always been frustrated by my lack of
>>methodological knowledge to be able to investigate graph theory and
>>develop algorithms etc. So I must sit on the sidelines.
>
>As already underlined by Hovenkamp, I don't think the problem is with graph
>theory first. It is with clarifying our goals and assumptions in
>biogeography, before we go and ask the "graph theory people" exactly what
>we need.

On this I take a different view. I don't see the need for further
'clarification' of goals and assumptions for panbiogeography. The method
already works, it is successful and the conceptual foundations for the
method show that graph theory may have a lot to offer in further
development of the method, particularly for quantitative analysis.

>Maybe one could contrast the spatial connections with the phylogenetic
>connections in order to test some model (e.g. that shortest distances
>should stand between phylogenetically closest groups for some reason, like
>a process of generalized speciation by vicariance and limited
>dispersal...). But to my knowledge this is not part of Panbiogeography
>presently, because Panb. is "just maps"...

I you read the chapter on Mapping the Trees of Life you will find such
considerations. If they should not be part of panbiogeography as you
reason, then on that we will just have to take a different view.

>By the way, you are considering a taxon, and sister groups relationships
>within a taxon. Seems clear that the taxon stands possibly above the
>species level. Do you have a criterion for fixing at what "level" you
>delineate a "taxon" you use in the analysis (because maybe the whole tree
>of life is a taxon...).

Any taxonomic level may be considered for analysis.

>This question is not specifically addressed to panbiogeography anyway.
>Rarely do biogeographers argue about this problem of delineation (should
>involve absolute datations in relation with geological features at stake?).
>
>>If one defines systematics broadly enough it could include biogeography.
>
>Are you suggesting to make localities or spatial distributions a taxonomic,
>or even phylogenetic, character? Combined with biological characters of
>organisms? Or rather characters for a separate classification ("Pacific /
>Atlantic organisms" for instance...) to be contrasted with systematics /
>phylogeny?

I'm not making any specific suggestions. One may take the view that
(pan)biogeography and systematics are separate disciplines, or one may take
the view that panbiogeography is in some way a subset of systematics. It
all depends on how one may wish to define the disciplines and their
operational relationships. When there is a complete correspondence of
homology between systematics and bigoeography (e.g. where biological
relationships are the subject of analysis) I can certainly see where
biogeography may fall under systematics.

>Seems that you are trying to deal with some "geographical taxa"
>(geographical relationships, tracks...) of GEOGRAPHY OF TAXA (spatial
>minimum spanning trees for localities of TAXA). Thus, "taxa" of geography
>of taxa.

Or it could be that the localities of taxa connect the tracks rather than
the other way around.

Of course one may examine the panbigoeography of characters too.

I think the questions raised here and by Hovenkamp show how much spatial
analysis lies outside traditional biogeographic discourse. I have suggested
before (perhaps this repitition cannot be forgiven) that panbiogeography is
not attractive to most historical biogeographers because most historical
biogeographers are biological systematists and therefore more comfortable
with  biology than geography. This I believe also has far more to do with
the lack of recognition given to Croizat (apart from the obvious problem
that he attached Darwin's methodology and synthesis) than how he wrote (I
acknowledge in anticipation that others of course will disagree).

John Grehan

Frost Entomological Museum
Pennsylvania State University
Department of Entomology
501 ASI Building
University Park, PA 16802. USA.

Phone: (814) 863-2865
Fax: (814) 865-3048

Frost Museum
http://www.ento.psu.edu/home/Frost/index.html




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