Biogeography of Dietes (Iridaceae)

[Ken Kinman]

John,
     I have little doubt that Dietes was once more widespread---I figured
that pretty much goes without saying (unless some Dietes seeds or plants
were somehow transported all the way from Africa to Lord Howe Island).
     In my opinion, the most likely wider distribution was southern Africa,
across parts of Antarctica, to the Australian region.  The cause of
extinction in Antarctica would have almost certainly been temperature
related (which again should go without saying).
     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.
      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).   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.
Otherwise I will assume Dietes most probably once lived in Antarctica.  I'd
rather call this one of the standard "Gondwanan" tracts (not an Indian Ocean
tract).  Is it this sort of thing that makes panbiogeography so unpopular?
            ------
                 Ken Kinman
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).  Maybe I am
over-extrapolating, but then again I think you may be prone to
under-extrapolate (especially when it comes to Antarctica).  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?

*****************************************
>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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