Comment on the biogeography of Humphries

John Grehan jrg13 at PSU.EDU
Mon Nov 13 09:18:26 CST 2000


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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