Biogeographic units and classification

[Jong, R. de]

Possibly I misinterpret John Grehan's discussion, but does not a baseline
connect two areas of endemism that are connected by phylogenetic
relationships of their inhabitants? If this is so, and if an area of
endemism is unnatural, does it become natural when it splits into two? Is
not a baseline a hypothesized biogeographical province or whatever in
another geological period? Why would such an area in, say, the Cretaceous be
more natural than nowadays? If we agree that biogeographic units are areas
of endemism (i.e., are characterized by endemic species), then they are
natural in the sense that they are characterized by natural (not man-made)
phenomena, notwithstanding the fact we may disagree about the limits of the
area.
Apparently, the problem arises from attempts to find a hierarchical order in
a system that did not per se develop hierarchically. Even in cases where we
can discern a hierarchical development of physical areas (sch as the
break-up of Gondwana, and not counting the fact that the pieces partly
became inbedded in or connected to areas wtih another origin), it remains to
be seen if distribution areas agree with that, and even if they do, why
neglect all the distribution areas that don't?
I fully agree with Peter Hovenkamp's comment that biogeography is a
discipline of its own, and that we should apply methods suited to
biogeographic problems. If in panbiogeography the principle of synapomorphy
has been established as a matter of methodological principle, it may well be
time to reconsider this principle.

Rienk de Jong


> -----Oorspronkelijk bericht-----
> Van:  John Grehan [SMTP:jrg13 at PSU.EDU]
> Verzonden:    maandag 26 april 1999 3:50
> Aan:  Multiple recipients of list TAXACOM
> Onderwerp:    Biogeographic units and classification
>
> Regarding Hovenkamp's comments on the differences between
> biogeography and biological systematics, the problem that
> remains is the question of establishing natural classifications in
> biogeography.
> Regardless of the differences between biogeographic and biological
> processes, biogeographers are involved in the construction of
> biogeographic units and natural classifications.
>
> The way I look at the application of systematics to biogeography
> involves the question of natural units and natural classifications. In
> biological systematics the status of "natural" lies in a shared history
> (monpophyly) indicated by the presence of uniquely shared characters
> (synapomorphy). If biogeographic units and classifications are not to use
> these
> principles, what are the alternatives for establishing that a
> biogeographic unit is natural as opposed to arbitrary?
>
>  In panbiogeography the biogeographic units are defined by
> baselines -spatial characters uniquely shared by those
> distributions whose tracks cross the baseline.
>
> Whether or
> not one might agree with this method, the criterion for natural
> unit is at least explicit and  testable. In contrast,
> Wallacean areas are not suported by any such criteria (Gary Nelson
> suggests that even Wallace did not consider them natural). If
> they are simply arbitrary constructs they would seem not to merit
> any scientific standing.
>
> In the case of panbiogeography at least, the principle of
> synapomorphy appears to have been established as a matter
> of methodological principle, rather than simply adapting problems
> to methods developed in another field.
>
> I would be very interested to know of criteria outside those of
> monophyly and synapomorphy whereby biogeographic units and
> areas might be considered natural. As far as I am able to discern
> at present, all geograpic areas, including areas of endemism, biomes,
> ecological areas, Wallacean areas, are all artificial constructions.
> That this is a minority and eccentric point of view I would agree.
>
> John Grehan