dispersal and biogeography

John Grehan jrg13 at PSU.EDU
Sun Oct 3 20:34:53 CDT 1999

>Yet, if I do recall correctly, Croizat himself used the term "dispersal",
>though in an unusual sense, in connection with his method. How can spatial
>relations be otherwise explained, if not through dispersal?

Correct, Croizat used the term dispersal, although to include both
migration of individuals and differentiation of taxa (dispersal =
form-making + translation in space).
In this way he provided a purely biogeographic definition of dispersal as
opposed to the ecological definition (dispersal = movement of individuals)
used by most biogeographers (at least all the dispersalist and vicariance
cladistic biogeographers whose works I have read).

>If one assumes, like Croizat, dispersal (or dispatch) through vicariance,
>dispersal routes should follow the movement and direction of tectonic plates?

I don' think I understand this point.

>Or in other words, is the understanding of the track as shortest line
>two points the direct translation of cladistics into panbiogeography, while
>Stuart Poss' idea would have roughly something to do with those that
prefer to
>figure out a process before starting a model....

The question of cladograms and track construction I will leave to experts
in the field. As the application of the two is currently used, only tracks
contain spatial information (biological cladograms contain no spatial
information, only the ordering of biological relationships between
localities or areas).

traditional biogeographers (both dispersalists and vicariance cladists)
have interpreted distributions according to ideas generated outside the
spatial structure of the pattern itself. Such ideas may be over centers of
origin and dispersal routes, or postulated paleogeographic and climatic
events. Since Stuart Poss does not appear to recognize spatial structure as
informative, he would fit into one of these or another category I would
assume (but I can be corrected on this).

John Grehan

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