Deleporte and Kinman on the Pacific

John Grehan jrg13 at PSU.EDU
Thu Jul 4 16:04:24 CDT 2002

Ken wrote wrote:
>     I guess I am going to have to try and get a copy of Seberg's 1988
>analysis sometime before commenting much more on Oreobolus.  But from the
>evidence I have seen, the Cenozoic radiation of Poales was largely from the
>south into the north (which was more devastated by the K-T event), and
>Oreobolus seems to reflect that pattern.

Do you mean that Oreobolus originated in to the south and then migrated to
the north? If so, what is the empirical biogeographic evidence?

>  If panbiogeography as presently
>practiced cannot accomodate testing using narrative approaches, then it's
>too restrictive for my tastes (and I will have to borrow from it without
>embracing it fully).

Panbiogeography is an independent science. It has its own methods and
concepts to analyze distribution patterns to generate hypotheses about the
past and the present. As an independent science it cannot be 'tested' by
the degree of conformity of its hypotheses with hypotheses generated by
other sciences (e.g. historical geology). If there is agreement then one
has corroboration. If there is disagreement one has a research anomaly.
Darwinian biogeography does not engage in any testing using geological
narratives, but simply attempt to provide explanations in the light of
those narratives. Also, I should emphasize that as an independent science,
the issue for panbiogeography is the biogeographic method, not whether or
not the phylogeny is absolutely determined to be 'true' or not. One can
take the same phylogenetic information and get different biogeographic
results using different biogeographic methods. One can have a 'prefect'
phylogeny and produce junk biogeography. That's at least one basic take
home message.

>     In any case, I believe your Oreobolus paper will be fatally flawed if
>your maps maintain that mid-Pacific baseline (with its big solid black
>square), especially if Seberg is right about distichus-goeppingeri being a
>derived clade (and thus having little relevance to the biogeography of all
>the earlier speciation in Oreobolus).

In presenting the arguments here it can be problematic in that Ken and
others may be not so well acquainted (if at all) with panbiogeographic
methodology so I should explain that the baseline represents the tectonic
feature crossed by the track. This feature is the Pacific basin as a whole,
and in terms of tectonic formation the principal feature  crossed is the
Pacific spreading ridge. Even thought the paper is formulated for
biogeographers I may add that clarification. So the baseline is not 'mid
Pacific' in terms of a particular locality within the Pacific. The baseline
applies to the genus as a whole, not just to its most derived clade. Since
the more primitive groups are connected to the trans-Pacific track this is
shown to be relevant in that they are still connected across the Pacific
basin rather than any other.

>     A more southerly baseline (as in your initial Oreobolus track map)
>makes more sense to me, except that I would go even further south, directly
>from New Zealand (or Tasmania) to the southern tip of South America (and not
>via Tahiti).

I think you are looking at the baseline as some sort of Darwinian center of
origin. It is not. The baseline orients the track with respect to a
geomorphological feature - in this case the Pacific. If one were to look at
any concept of 'center' for the 'origin' of Oreobolus, that center is the
Pacific basin.

>Once Oreobolus is found in the Antarctic fossil record,
>spanning tracks that are even more southerly and shorter can be shown via
>that land bridge.  That's the narrative I predict future evidence will bear
>out for Oreobolus (and a lot of other taxa).

The occurrence of Oreobolus in the Antarctic will change nothing with
respect to the biogeographic homology of the genus. That homology is
Pacific. A Darwinian biogeographer may invoke the Antarctic as a landbridge
connecting migrations between the Old and New Worlds, but this view is not
derived from the empirical evidence, but rather a preconceived model of
centers of origin invented by Darwin to 'explain' distributions in the
light of current knowledge.

>         ------- Ken Kinman
>P.S.  It was suggested to me privately that O. furcatus might have been
>spread to Hawaii and Tahiti by birds (perhaps through their droppings?).  I
>don't know enough about Oreobolus dispersal mechanisms to really rule out
>humans or birds or anything else, especially if we don't know how long ago
>such dispersals occurred.

The interesting aspect of these records is that the biogeographic
connection is shared by other taxa, including distinct species. Perhaps
birds picked up some of the marine shorefishes and deposited them at one or
other of these localities too? I say this to emphasize that one may invent
any number of stories to disperse organisms from one end of the earth to
the other. Individually they may have the cloak of plausibility, but
treated together the distribution patterns defy correlation with common
means of dispersal while showing congruence with tectonics. That aside,
some of Ken's comments about Oreobolus may be useful in finalizing the
manuscript before submission for publication and I welcome his thoughts, as
I also do for Pierre.

John Grehan

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