More on Biogeographic memory

John R. Grehan jrg13 at PSU.EDU
Tue Oct 9 16:25:14 CDT 2001


Regarding Pierre Deleporte's comments


Some of the philosophical issues over whether a method is just 'descriptive'
as opposed to anything else are perhaps out of my depth. Whatever one might
classify of panbiogeograpahy, the method has worked in that it has
delineated the main spatial structure of biogeography for the world, and
that it has led to novel geological predictions that competing research
programs failed to generate. In this way panbiogeography is progressive.
Application of the method since Croizat has demonstrated the spatial
relationships of 'many' distributions with tectonic structures in places
such as New Zealand, North and South America, and South East Asia. Its
application to New Zealand biogeography led to the formulation of the
'parallel arcs model' as a new alternative synthesis of geology and biology
for the region.


>I understand quite well the insistence of John Grehan that a biogeographic
>unit (area or else...) should better not be arbitrarily defined a priori,
>but rather emerge from some explicit analysis.

My present view is that any 'area of endemism' is arbitrary in its
geographic delineation and therefore not a natural biogeographic unit of
analysis.

>But Hovenkamp is correct in stating that the
>book does not explain how to implement this when dealing with the
>"hierarchy of sister-groups" constituted by a phylogeny, and its relative
>temporal dimension (which Hovenkamp 1997 attempts to take explicitly into
>account in his own approach).


I agree, we did not go into drawing tracks for heirarchies of phylogenetic
relationships in the book. One approach would be to link taxa by a minimal
spanning link in the order of their biological relationships. Another might
be to link taxa by minimum distance alone and compare for congruence with
closeness of biological relationship. Incongruence might offer potential
for further evaluation.

>  The line or track has to cross the separation or barrier.

It has to cross the 'separation' in order to map the 'space' between.

 From deep in the woods,

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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