Vicariance patterns and baselines

[John Grehan]

>Pierre deleporte wrote:
>Now, the Panbiogeographic approach gives a same track for both taxa (Asia -
>America - Africa), but with a baseline across Pacific for ((a,b)c), and a
>baseline across Atlantic for ((A,B)C).

Actually that would be two different tracks. One track being Pacific and
one Atlantic. As the hypothetical description goes, the distributions are
too vague for me to assess in any meaningful way.

>In this example, the Panbiogeographic approach does not use the
>phylogenetic information that taxa in Asia and America are closest
>relatives in both cases, which seemed relevant for vicariant explanation.
>Instead, it considers the relative diversity of more or less related taxa
>on different continents.

One could, however, use the phylogenetic information to link the
localities, and the main massings to distinguish different baselines. The
other consideration is for the same distribution but two groups, one being
(a, c) b, and other (a, b) c.

>A problem, in my view : rates of speciation, or rates of survival of
>species, may perfectly be linked to environmental conditions prevaling on
>different continents, and thus would have no connection with the Pacific or
>Atlantic "tectonic history".

These theoretical issues are certainly there for one to debate. I admit to
not being a great theorist so I will look forward to reading publications
on such topics. It might prove to be the case that panbiogeography fails
all manner of academic and philosophical 'standards'. One may accept those
standards and stay with Darwinism. Certainly the demonstration that
panbiogeography meets standards of progress (such as being a progressive
research program) has made no difference the other way (i.e. having
demonstrated the lack of theoretical and empirical progress in the
Darwinian method one did not see Darwinian biogeographers give up their
method).

The theoretical examples presented are fine as a rhetorical device, but I
prefer to use actual examples where I can see the actual geography of
distributions. To say something occurs in 'America', for example, is not
very informative for me.

John Grehan