panbiogeographic trivia

[John Grehan]

I recently had the opportunity to look at Brown and Lomolino's
second edition of Biogeography. There are some statements about
panbiogeography that lead me to comment for those few who may
be interested in such trivia.

In their glossary they define panbiogeography as a sub-discipline of
vicariance biogeography. Rather ironic in that panbiogeography
preceeded vicariance biogeography (of the US school - agreed some
cladists were doing area cladograms as early as the 1920's).

Further irony of this claim is their acknowledgement that panbiogeography
draws tracks connecting the locations of related taxa. These tracks involve
spatial homologies whereas vicariance cladistics requires biological
homologies.

It was interesting to see that supporters of panbiogeography are "zealous
disciplies".
The quasi religeous tones of such a description seem obvious, and naturally
supporters of alternatives a not "zealous disciplies".

The authors quote vicariance cladists to support their contention that most
biogeographers
recognize Croizat's approach as flawed by its unrealistic and idiosyncratic
assumptions.
To my knowledge, none of the papers they cited establish this contention.
In fact the
paper by Morrone and Crisci which they cite in the dismissal of
panbiogeogrpahy,
while emphasising the value of vicariance cladistics, actually gives
explicit recognition to the
need for spatial homology using panbiogeographic proceedures BEFORE carrying out
cladistics analyses.

I get the impression that Brown and Lomolino, in their drive to dismiss
panbiogeography,
 have not bothered to read papers properly.

There are some interesting contrasts between Brown and Lomolino and the earlier
Brown and Gibson 91983). Despite the stronger anti-panbiogeographic theme, the
section was changed from Vicariance Biogeography to Panbiogeography and
Vicariance Biogeography - thus giving added emphasis to the distinct nature
of panbiogeography despite trying to subsume it under vicariance biogeography.
Panbiogeography was also added to the glossary.

Brown and Lomolino state that Croizat opposed Wegnerism, but never bother to
state why (the reason being that Wegener's model did not allow for former
Pacific land connections. Brown and Gibbson note that Croizat later reversed his
stand. This is not true. Croizat came to accept drift as a more probable
geological
mechanism, but he did earlier allow for either drift or sinking as
mechanisms that
could both result in disjunection. In Croizat's view, Wegener's model was
deficient
with respect to the Pacific.

Brown and Lomolino propose several reasons for the lack of favor given to
Croizat's ideas, but one they miss out on is that of geography. Most biologists
appear to dislike or are suspicous of geography as having empirical
content. This
is based, I agree, on my own experience with biogeographers working with
historical
biogeography. Most appear to be little interested in maps of distributions, and
even less that such maps hold empricial content that can be analysed using
geographic (spatial) characters.

Brown and Gibson's claim Croizat's insistence that long-distance dispersal had
to be dismissed for explaining disjunections was replaced by Brown and
Lomolino's
contention that Croizat categorically rejected dispersal over long distances and
across barriers to account for generalized tracks. The former statement is
certainly
incorrect. The latter is more complex. Crpozat emphasised averages of
performance,
so that for a generalized track he considered it unlikely that the pattern
between
continents was entirely due to trans-oceanic disperson on the modern map. This
did not preclude the possibility that some members of the track did disperse
independantly of the geography that influenced the main pattern. Craw (1989)
illustrated this in quantitative analysis. To get  a generalized track
it is necessary for dispersal to take place so dispersal itslef is never
precluded.
The question becomes one of what kind of geography did such dispersal
take place.

If anyone thinks the above comments are no fair or inaccurate please feel
free to respond.

John Grehan