Panbiogeography of the Americas

John Grehan jrg13 at PSU.EDU
Sat Oct 2 16:34:00 CDT 1999

Thomas Schlemmermeyer wrote

>Let me, just for the fun of it, throw in my impression while reading Croizat.
>Croizat's problem apparently were not marine organisms, it were plants.

Plants were the primary database in Manual of Phytogeography, but I have
never added up the examples to see what predominates in Panbiogeography
etc. Most examples did deal with land organisms, but marine examples were
included. Further, Heads (1983) commented on the parallel track structure
of marine shorefishes and terrestrial organisms in the Pacific.

>As the Croizat machine is an enormous data file of monographies, check-lists
>and so on, the task to reinvent it seems to me rather the task to check these
>logical connections above mentioned and how they tie in with overall observed

That would be a worthwhile endevour I would think.

>Of course, marine organism are a special case

Not really, in that just like terrestrial distributions in marine organisms
there are widespread taxa, and locally endemic taxa, widespread species and
locally endemic species. Tracks can be applied to marine distributions in
the same way as on land.

Stuart G. Poss wrote

 Because of the Coriolis force and because
>>continental margins create obstacles around which fluids and the
organisms in
>>them must flow, they seldom travel in straigh lines of minimum distance.

I don't understand how this relates to the track method which is about
spatial relationships, not about dispersal routes (although one might apply
the method to such consderations).

>>non-linear coastal margins will confound the approach when dealing with

I'm not sure this is a particular problem. One may have a coastal taxon
along the coast of South America, eastern and western coasts of Africa and
Madagascar. The track method would specify an Atlantic Ocean basin connection
implying that the history of this distribution is more likely involved with
the Atlantic
rather than eastern Indian Ocean, Pacific, Arctic or Southern Oceans. One
hypothesize that the distribution originally went across these oceans and
the present pattern is extinction so the Atlantic baseline is an artifact.
Should evidence be produced
(such as fossils then one could support such a possiblity). In the absence
of such information it is not necessary. In the same way Nothofagus is a
Pacific group based on available distribution information even though its
always possible that the taxon was really always widespread through Africa
and India.

John Grehan

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