Biogeography and geological evidence etc.

[john grehan]

Peter Stevens wrote:

>Question (and I apologise for reopening a can of fat and very wriggly
>worms): could geological evidence/theories/hypotheses ever be
>relevant to your thinking?  If so, perhaps you could suggest what
>kind of information might be suitable.

Its a good question that needs no apology.

In panbiogeographic method the primary geological 'evidence' to be included
in the methodological analysis is the correlation of tectonic structure
(pattern) and biological pattern. It is from that correlation (whatever
that may be determined) that one may have a basis for exploring the
historical implications of particular geohistorical theories or hypotheses.
For example, while one my find an organism either side of the Atlantic it
is not until a biogeographic criterion is provided for correlating that
distribution with Atlantic geology that one may have a methodological basis
for then considering the relevance of any geohistorical theory about the
Atlantic. The fact that the two organisms are most closely related does
not, alone, provide this link as the geography of that link could be in any
number of directions around the globe that does not include the Atlantic.
Under the minimal spanning link (MSL) and main massing criteria one would
select the Atlantic as the relevant tectonic sphere of interest, and from
there one may consider historical hypotheses - but those theories or
hypotheses neither validate or invalidate the purely biogeographic
(spatial) homology determined by the MST-main massing criterion.

An illustration of the method with respect to geohistorical theory can be
found in Craw's (1989) paper where he examines the different track
homologies involving the NZ mainland and the Chatham Islands where two
competing geohistorical models are involved.

In the Galapagos paper I describe how Croizat predicted the tectonic
significance of the Galapagos from biogeographic patterns before the
tectonic structures of the seafloor was documented. It is this correlation
that may have more significance for understanding the origin of the
Galapagos biota than whether one believes in this or that geohistorical
theory for the area (and there are at least four major competing
geohistorical-tectonic theories for the region). The predicted correlation
actually allows the biogeographer the opportunity to suggest which model or
models may be more representative of history than the other way around.

All of this is very brief and perhaps an over simplification. In the recent
literature the papers of by Heads on New Guinea provide some detailed
examples involving track and tectonic correlation along with their
geohistorical implications.

John




>P.