Biogeographic areas of Raven and Axelrod

[P.Hovenkamp]

At 09:28 PM 20-04-99 -0400, John Grehan wrote:

(...)
>I appreciate that there are probably not many systematists interested in the
>principles of systematc classification applied to biogeographic homology, but
>of those who do I would be interested in comments that can establish that
>the biogeographic areas referred to by Raven and Axelrod (or even those of
>Wallace) do conform to generally accepted principles of synapomorphy and
>monophyly.

Before we can start to establish that this is so, or not, as the case may
be, I think we have to establish that the principles of synapomorphy and
monophyly are useful in a biogeographic context. I very much dispute that
they are.
These principles were developed in a systematic context.
Monophyly applies to a system in which the basic units (species) undergo
evolution which is fundamentally divergent, thus leading to an inclusive
hierarchy (with monophyletic higher units)
Synapomorphy applies to a system in which traits are developmentally tied
to the units, and are being modified in (fundamentally) an irreversible
process. Thus, whenever we find a modification, we can asume that it arose
either on the current carrier or on one if its ancestors.
These two processes (descent & modification) are fairly well covered by a
by now fairly well established theory (the so-called Theory of Evolution).

In a biogeographic context, none of this applies.
Whatever evolution the basic units in biogeography are subject to, it is
not divergent (unless we restrict ourselves to only the divergent
episodes). Should we want to consider only basic units that undergo
divergent evolution only, we would have to discard at the same time a
number of well-established theories about geophysics and historical
geololgy. Therefore, monophyly is not applicable to biogeographic units.

Whatever characters biogeographic units carry, that are not tied to it
developmentally, so if we find a modification, we cannot be sure that it
arose on the current carrier or on one of its direct ancestors. Thus,
synapomorphy in its current meaning cannot be applied to the biogeographic
"characters".

Summing up: biogeography is not "systematics at another level", it is a
discipline of its own. Biogeographers would do better to search for methods
that fit its problems, than to try to fit the problems to methods developed
in another field.

Peter Hovenkamp




P. Hovenkamp
Rijksherbarium, Leiden
The Netherlands
hovenkamp at rhbcml.leidenuniv.nl
http://rulrhb.leidenuniv.nl/