[Re:] Comment on the biogeography of Humphries

Thomas Schlemmermeyer termites at USP.BR
Mon Nov 13 14:39:01 CST 2000


I only dimly recall the papers by Croizat I read but nevertheless I may throw 
in the following:

Croizat explicitly mentions the law of great numbers by Bernouli. I do confess 
that my statistics is not good enough in order to apreciate whether Croizat 
correctly referred to BernouliĀ“s law, but the point which Croizat intended to 
make is the following:

When nodes and tracks coincide for many different taxa this cannot be 
coincidence. So if there is such an event (many coinciding tracks and nodes for 
widely different organisms), one may look for underlying mechanisms, processes 
and so on.

Indeed, as far as I further dimly recall, one of the panbiogeographical, 
methodological questions centers around the problem of discerning accidental 
nodes and tracks from meaningful ones. 


On (         Mon, 13 Nov 2000 09:18:26 -0500),         John Grehan 
<jrg13 at PSU.EDU> wrote:

>
>I received a response concerning my biogeography posting that was addressed
>only to me. Since some of these comments deal with general issues I have
>attached them below without the author name.
>
>
>I have read your book on panbiogeography with interest, but I still can't
>answer this question: why do you consider that the absolute linear distance
>between the location of organisms on the map makes any sense at all? Some
>are close together, some are distant, but what does this mean biologically,
>or biogepographically? What is the general mechanism, or process, you
>assume to be governing geographical distribution in order that the
>distances make any sense at all, and can be interpreted some way or
>another? (An example: 100 km across the barrier of the Himalayas or 100 km
>across the plains of Siberia always make 100km distance for "track
>analysis" if I understand well...).
>
>A possible answer could be the assumption of some regular dispersion in an
>isotropic world: being closer to one another would generally make sense in
>terms of likelihood of the distributions... But it is your approach, and
>you should know better than I do.
>
>On the other hand, if there is no answer to this question, then the tracks
>of panbiogeography could be an exploratory tool, like the "data anlysis"
>methods of the French school which use the grouping of objects on the basis
>of overall similarity (same classificatory tools as in "phenetics") in
>order to look after some correlations to be explained.
>
>With this simple example, I just want to illustrate that:
>-       "explain" or "explore" are not the same problem at all;
>-
>- I can't figure exactly what the absolute-distances-based "tracks" mean if
>there is no clarification of there underlying assumptions (or lack of).
>
>****************
>
>I feel the above points identify the potential complexity of the geographic
>problem and provide an indication of the range of issues that can be
>addressed in the future development of geographic biogeography. I would not
>claim to hold the ideal answers to these questions and rather view them as
>fields of exploration. In panbiogeography both the mechanism and
>methodological approach has been considered in understanding the utility of
>track construction. Henderson (1990) attempted a biological analogy with
>ecological dispersal while Craw and others have emphasized parsimony for
>minimum distance. Even then, this is in the absence of other information
>(e.g. main massings, phylogeny).
>Perhaps in the future biogeographic methodologists will put the same energy
>into the issues of spatial representation and construction as has been put
>into cladogram construction but then will that necessarily bring greater
>clarity?
>
>A key difference, in my own opinion, between area cladistics and
>panbiogeography is that the former (in its pure form) ignores the spatial
>problem while the latter attempts to address it. Croizat not only
>established a methodological foundation for this problem, but one that
>appears to work by generating successful novel predictions. But it would be
>a mistake to consider the minimum distance criterion uncritically. Croizat
>did not always use this criterion, at least as an absolute. Some tracks are
>drawn as circuits, some parallel geomorphological or geotectonic features
>so there is yet a lot of room for future development of the method and
>synthesis. I would be the first to insist that there is a lot of room for
>creative potential in panbiogeography. One need not be fettered by the present.
>
>John Grehan
>
>


	  	  




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