[Taxacom] Seed plants of Fiji

[John Grehan]

Karl,

Thank you for the clarification of your perspective. I can see that it
is the traditional view that geological theory (i.e. interpretation of
the evidence) determines biogeographic theory. You say "there is no
evidence at all that the Hawaiian Islands have been anything other than
always isolated". One would need to ask what "evidence" you would
require. If you are looking only for the presence, for example, of
continental rock remains, you might never find evidence (although such
evidence has been found for at least one mid Atlantic ridge island). 

But then what is the total scope of evidence that may bear on this
question? Years ago Mayr said that the idea of geological connections
between the Galapagos and America was nonsense because there was no
geological evidence - this evidence being the presence of continental
rock. But he somehow managed to overlook the geological models calling
for the presence of on or more extensive island arcs in the eastern
Pacific that may have crossed the Galapagos and left some of their biota
behind. Since the history of the earth involves mobile structures one
would need to ask whether anything has transpired in the former Pacific
as is accepted for the Atlantic and Indian oceans? 

Even though there is no consensus on the geology of the Pacific amongst
geohistorical theorists, there are some theories out there about mobile
geological elements that have existed in the Pacific that could have
left their biota behind that survived as meta-populations as proposed by
heads. This origin would make sense of the extensive vicariism of
related taxa in the Pacific even though the individual taxa may range
over many islands.

If one limits geological 'evidence' to the rocks themselves and the
accepted interpretations of geologists biogeography will never be a
science since it cannot independently predict history. As for Hawaii
there is indeed biogeographic evidence for its biota having been
inherited in part from an in situ Pacific biota. Please keep in mind
that if Croizat limited his evidence to geology he could never have
successfully predicted the composite tectonic structure of the Americas,
the island arc origin of the Galapagos biota, or similar geological
processes in other parts of the planet.

John Grehan





Dr. John R. Grehan

Director of Science and Collections

Buffalo Museum of Science1020 Humboldt Parkway

Buffalo, NY 14211-1193

email: jgrehan at sciencebuff.org

Phone: (716) 896-5200 ext 372

 

Panbiogeography

http://www.sciencebuff.org/biogeography_and_evolutionary_biology.php

Ghost moth research

http://www.sciencebuff.org/systematics_and_evolution_of_hepialdiae.php

Human evolution and the great apes

http://www.sciencebuff.org/human_origin_and_the_great_apes.php

 

> -----Original Message-----
> From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-
> bounces at mailman.nhm.ku.edu] On Behalf Of Karl Magnacca
> Sent: Wednesday, November 15, 2006 7:46 PM
> To: taxacom at mailman.nhm.ku.edu
> Subject: Re: [Taxacom] Seed plants of Fiji
> 
> On Wed, November 15, 2006 2:36 pm, John Grehan wrote:
> > What is the Lemuria remark supposed to mean? Does it mean that you
have
> > already decided the answer to the Pacific that does not allow for a
> > vicariant origin?
> 
> Well, you have an isolated hot-spot* island chain, with slopes that go
> straight to the abyssal plain.  Even where there are undersea
connections
> between islands, aside from Maui Nui and Oahu they are thousands of
feet
> deep.  A check of the seafloor shows no major features for almost 2000
> miles around, except for some rifts on the seafloor a few hundred
miles
> southwest of Gardner.  All the islands are more or less circular,
modified
> by volcanic rifting, with no faulting that would indicate separation
from
> another, missing land mass.
> 
> * - there is some dispute about the standard hot-spot model, but AFAIK
the
> alternatives don't mention connection to other land masses.
> 
> So to answer your question - yes, I have already decided that my
> conception of the Pacific does not allow for a vicariant origin of the
> Hawaiian biota.  Not from jumping to conclusions based on
preconceptions,
> but because there is no evidence at all that the Hawaiian Islands have
> been anything other than always isolated.
> 
> If you want to argue about the Fijian biota being vicariant, I might
buy
> that.  But for anything east of Tonga, you're stretching credibility.
> 
> Karl
> 
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