Biogeography of Dietes (Iridaceae)

Wed Jan 22 21:36:53 CST 2003

Ken Kinman wrote:
>John,
>     I have little doubt that Dietes was once more widespread-

I agree, this is implicit in the track homology.

>     In my opinion, the most likely wider distribution was southern Africa,
>across parts of Antarctica, to the Australian region.

Perhaps, but the track contains no such information. One may speculate on
such possibilities, but I am not aware of any biogeographic evidence in
that direction.

>The cause of extinction in Antarctica would have almost certainly been
>temperature
>related (which again should go without saying).

If it was there, which seems at this point to be pure speculation. One may
speculate that Dietes was also in Greenland, Russia, Europe etc.

>     What possible alternatives are there?   Africa through southern Asia to
>the Australian area, followed by total extinction across southern and
>southeast Asia?   Or island hopping across the Indian Ocean followed by
>extinction on all those intervening islands?  Remote possibilities, but
>extremely doubtful in my opinion.

I cannot comment informatively on such speculations. The track homology
suggests that the evolution of Dietes is most closely bound with the
geological history of the Indian Ocean.

>      Dietes may well have arisen in southern Africa and then spread across
>Antarctica and to the Australian area (although I would personally lean more
>towards it having arisen in Antarctica and spread in both directions).

Again, there is no evidence I know of for suggesting such a scenario.
Dietes may well have arisen across Africa and the Australian area together
rather than one before the other.

>  If you can provide empirical evidence that Dietes naturally occurs in some
>place like Malaysia, I will retract my statements and admit I am wrong.

I don't see any localities having any bearing on the matter as there is
nothing empirical in the biogeography to support any of the speculations.

>Otherwise I will assume Dietes most probably once lived in Antarctica.

One is free to do so. It is possible, but it is simply speculation that I
do not see as being derived from the current biogeography which does not
delimit the former distributional range.

>  I'd rather call this one of the standard "Gondwanan" tracts (not an
> Indian Ocean
>tract).

The Indian Ocean is a tectonic formation. Gondwana is a geohistorical
theory which is not synonymous with the Indian Ocean and panbiogeographic
analysis does not involve homology being determined by selected
geohistorical narratives.

>Is it this sort of thing that makes panbiogeography so unpopular?

I've said before that what might make panbiogeography so unpopular (and
here one needs to be more specific as to so unpopular where? Certainly it
is 'unpopular' in much of the Anglo-Saxon dominated world, less so in some
other spheres) is the dislike of most biologists, and certainly most
systematists, for geography.

>P.S.  I see no good reason to disbelieve that Lord Howe Island has been
>above sea level for only around 7 million years and that its Dietes
>population most likely came from Australia, New Zealand, or New Caledonia
>(which are where most of its flora and fauna came from).

If one takes gehistorical narratives as the basis for biogeographic
reconstruction then biogeography has no empirical input - biogeography is
rendered empty of empirical content.

>Maybe I am
>over-extrapolating, but then again I think you may be prone to
>under-extrapolate (especially when it comes to Antarctica).

I did not extrapolate at all.

>I think science
>advances more quickly with mild over-extrapolations than it does using too
>much conservative under-extrapolation.  Isn't that what Darwin meant with
>his famous quote about speculation?

But then, Darwin got biogeography wrong.

John

>*****************************************
>>From: john Grehan <jgrehan at SCIENCEBUFF.ORG>
>>Reply-To: john Grehan <jgrehan at SCIENCEBUFF.ORG>
>>To: TAXACOM at USOBI.ORG
>>Subject: Re: Biogeography of Dietes (Iridaceae)
>>Date: Tue, 21 Jan 2003 13:15:40 -0500
>>
>>I managed to obtain a couple of off-list responses confirming the taxonomic
>>status of the Lord Howe species and also the distributional information -
>>for which I am most grateful.
>>
>>Although Ken is not sure about Dietes being a standard Indian Ocean pattern
>>I can say with surety that it is because its distribution includes Africa
>>and the SW Pacific. This is a common pattern for Indian Ocean groups. Its
>>as simple as that.
>>
>>As to Lord Howe Island, it is possible that the specie did not come from
>>any surrounding island, but represents local survival from a widespread
>>ancestor that occupied Africa and the SW Pacific. One might argue from a
>>stratigraphic point of view that Lord Howe Island is not old enough, or
>>been above water long enough. These are geological theories that may or may
>>not be true, and are contingent upon theories about the geological
>>formations of the immediate area. Thus one cannot presuppose that these
>>theories are anything more than just that and the biogeographic picture
>>does not have to be made subordinate to those theories - whether or not
>>Dietes is ever discovered to occur in the surrounding region.
>>
>>There is no biogeographic evidence (i.e. spatial homology of the known
>>distribution) to suggest either way whether or not Dietes once occupied
>>Antarctica. There is certainly no empirical evidence of it having
>>'originated' anywhere beyond its current track.
>>
>>John
>>
>>At 03:18 AM 1/21/2003 +0000, you wrote:
>>>John and others,
>>>     I'm not sure I would call it a "standard" Indian Ocean biogeographic
>>>pattern.  I see no reason to expect that Dietes ever occurred much
>>>further north than its present relict distribution.  I would guess it
>>>once did very well in Antarctica (possibly where the genus originated).
>>>     The big question is where the Lord Howe Island species came
>>>from----presumably New Zealand, Australia, or perhaps even New Caledonia.
>>>Whether relict populations of Dietes might still occur "naturally" in any
>>>of those places is hard to say (but it wouldn't surprise me if they did).
>>>        ----- Cheers,  Ken
>>>P.S.  This opinion is offered free of charge, although I think it's worth
>>>at least the proverbial "two cents".  Only time will tell.  :-)
>>>
>>>*****************************************
>>>>From: john Grehan <jgrehan at SCIENCEBUFF.ORG>
>>>>Reply-To: john Grehan <jgrehan at SCIENCEBUFF.ORG>
>>>>To: TAXACOM at USOBI.ORG
>>>>Subject: Biogeography of Dietes (Iridaceae)
>>>>Date: Fri, 17 Jan 2003 09:54:31 -0500
>>>>
>>>>A paper by Goldblatt (1981) documents the distribution of this plant
>>>>genus with an East African range for five species (southern Ethiopia to
>>>>the Cape) and Lord Howe Island (one species). This is of course a
>>>>standard Indian Ocean biogeographic pattern (East Africa-SW Pacific).
>>>>Would anyone on this list know whether there have been any further
>>>>distribution records or phylogenetic treatments of its phylogenetic
>>>>relationships with other
>>>>Iridaceae published since the time of this article?
>>>>
>>>>John Grehan
>>>>
>>>>John Grehan
>>>>Director of Science and Collections
>>>>Buffalo Museum of Science
>>>>1020 Humboldt Parkway
>>>>Buffalo, New York 14211-1293
>>>>Voice 716-896-5200 x372
>>>>Fax 716-897-6723
>>>>jgrehan at sciencebuff.org
>>>
>>>
>>>_________________________________________________________________
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>>
>>John Grehan
>>Director of Science and Collections
>>Buffalo Museum of Science
>>1020 Humboldt Parkway
>>Buffalo, New York 14211-1293
>>Voice 716-896-5200 x372
>>Fax 716-897-6723
>>jgrehan at sciencebuff.org
>
>
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