Agreement yet?

John R. Grehan jrg13 at PSU.EDU
Thu Jul 11 16:35:40 CDT 2002

>  I would like to hear some response on - especially from the
> panbiogeographers.

I guess I can't resist an invitation like that. Hopefully without regret.

>To be blunt, I don't really see how it is possible to do biogeography in a
>manner, above the species level, without having a phylogentic relationship
>already in hand.

I don't intend to speak on behalf of anyone but myself. In general one has
a biological hypothesis of relationship, and biogeography may generally
proceed from that point. This of itself does not preclude geographic
relationships being considered (should done wish to) to evaluate the
phylogeny in question or to even offer a hypothesis of relationship before
the biological analysis is carried out.

>It is my sense that this was a major point that Nelson and Platnick
>made when they tried to integrate some Hennigian principles with Croizatian
>biogeography. I think that they were absolutely correct in trying to do
>so, though I get
>the sense that modern panbiogeographers are not all that enamored of their
>in this regard.

My view is the 'integration' between Hennigian principles and biogeography
and Croizatian biogeography never occurred. It was simply a rhetorical
claim. Vicariance biogeographers first claimed tracks to simply be area
cladograms mapped out geographically, but they never applied the minimum
spanning criterion that would make that relationship effective. If they had
it might be that their claim would be substantiated. Platnick and Nelson
(1988: 417) admit they may have been wrong in their earlier supposition of
panbiogeography and cladistics being interrelated in the form of vicariance
biogeography as expressed in Nelson's (1973) view that tracks are
phylogenetic trees mapped according to the criterion of a minimal
geographical spread. So it would seem that panbiogeographers are not alone
in not all that enamored of their efforts.

>Am I right in sensing this - and could the panbiogeographers explain what
>exactly are
>their views on this subject?

My individual view is that biological relationships (whether a cladogram or
anything else) contain no explicit information on what geographic space is
'crossed'. Without such a criterion biological cladograms are
geographically uninformative since the potential geographic connections are
infinite. Track analysis provides one method for designating relevant
geographic space. Incongruence between biological relationships and minimum
geographic space represents a potential focal point for drawing attention
to the possibility of phylogenetic reassessment. I am not well enough
versed in this aspect to speak with any authority, but I at least see the
possibility. If a phylogeny is weakly supported, for example, the
geographic incongruence may have greater influence than for a strongly
supported biological tree. One may take a look at other sources of
corroborating information such as with the example of Ficus relationships
where Croizat proposed an alternative phylogeny for a particular groups of
Ficus based on geographic proximity and main massings that seemed to find
corroboration in the phylogeny of some wasp pollinators.

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

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