More on Biogeographic memory

John R. Grehan jrg13 at PSU.EDU
Fri Oct 12 13:11:33 CDT 2001

>I just want to emphasize the possibility of practising an "ecological
>screening" of the taxa we use, according to different biogeographic
>problems at stake.

In panbiogeographic methodology the shortest line length provides a
criterion for track construction IN THE ABSENCE OF OTHER INFORMATION (sorry
- caps just for emphasis). So I concur with Deleporte that one may draw
this minimum distance in other ways other than by a simple straight line.
As long as the criteria are explicit the choice is open to critique. In a
forthcoming paper on the Galapagos I drew a track between southeastern
Brazil and the Caribbean with a line around the coast of S America rather
than across the interior to take into account the coastal habit of the
organism in question with the supposition (that might be wrong!) the
ancestral distribution of that organism did not include the interior. When
one looks at Croizat's tracks one can see that they are sometimes drawn
other than a strictly straight line - sometimes they follow geomorphology
for example. There are many possibilities for track construction and even
though our book emphasized the strict minimum spanning tree this is not to
preclude those alternatives.

>Yes, but congruence between distribution of taxa with comparable ecological
>skills, so that a "barrier inducing vicariance" for instance could
>potentially make sense for all of those taxa.

What may be interesting is the spatial congruence of groups that do not
have comparable ecological 'skills.' This was a major finding in Croziat's

>But I want to emphasize the point that even with such an approach, the fact
>that fishes don't fly will have to get into the reflection, sooner or
>later... and why not sooner? Comparing the pattern resulting from the
>analysis of fishes with RIVER spatial network seems to make sense.

So is this to say that comparing a distribution pattern of butterflies (for
example) with river spatial networks could not make sense?

>relation between long-term survival / dispersal abilities of the taxa
>(fishes...) and the geological features at stake (rivers, savannas,
>mountains, oceans, abyssal hotsprings...) makes sense in my view, and this
>involves more argument than merely "sister-groups plus distances".

The problem in biogeography is that the link between a distribution and
such geological features has been arbitrary. Often the choice appears to be
minimal spanning (baseline) links as the implicit operational procedure.
Even vicariance cladists to this sometimes while claiming their choice came
from the cladogram when it in actual fact came from spatial criteria.

>- but also avoiding to apply blindly a unique rule for analysing spatial
>distribution of any kind of living features, taking the map as a "tabula
>rasa" and shortest distances as obligatorily relevant.

As far as I am aware, panbiogeography is the only historical biogeography
method that provides an explicit formulation of spatial relationships. As
above, I would agree that the minimum distance criterion is only one way of
mapping spatial relationships. So far it has been very successful indeed in
mapping the global structure of biogeography with its successful
(corroborated) geological predictions and even some biological predictions.
As far as I am aware no one has demonstrated that any of the standard
tracks proposed by Croizat do not really exist - although Cox did
characterize the Pacific tracks as an illusion because his geological
perspective did not agree with them).

>I agree with Grehan, Hovenkamp and others that some approaches seem to take
>too little care of the map (limited set of predefined "areas"...), but
>others tend to consider the map as a white sheet with just distances
>reported on it... maybe we can go beyond this and improve adjustment of the
>tools to the problematics.

Further developments in spatial analysis for historical biogeography would
be very welcome. I have always been frustrated by my lack of methodological
knowledge to be able to investigate graph theory and develop algorithms
etc. So I must sit on the sidelines.

>The presentation of a method in biogeography should ideally begin with
>statements of this kind (exactly as for methods for phylogeny
>reconstruction: which process is required for the particular kind of
>pattern to make sense?).

This is just one opinion of what is ideal. There will no doubt be others.

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

More information about the Taxacom mailing list