[Taxacom] Pacific biogeography

John Grehan calabar.john at gmail.com
Mon Dec 17 15:31:08 CST 2012

One can understand such vague assertions about stepping stones if one is
not familiar with the panbiogeographic studies in question.

John Grehan

On Mon, Dec 17, 2012 at 10:34 AM, Richard Zander
<Richard.Zander at mobot.org>wrote:

> What an interesting note, Michael. If there were lots of islands in the
> Pacific long ago, their existence would likely explain certain
> distributions.
> Facts about sea floor subsidence may lead to good, pursuable scientific
> theories, which, though having to do with historical science, are
> nevertheless in the broad range of scientific ratiocination.
> The problem is with panbiogeographic analysis, the method of which is
> questioned. New facts about the possibility of lots of stepping stone
> islands in the Pacific may not make panbiogeographic "tracks" more
> revealing of historical processes. Submerged islands make poor
> repositories of evidence.
> ____________________________
> Richard H. Zander
> Missouri Botanical Garden, PO Box 299, St. Louis, MO 63166-0299 USA
> Web sites: http://www.mobot.org/plantscience/resbot/ and
> http://www.mobot.org/plantscience/bfna/bfnamenu.htm
> Modern Evolutionary Systematics Web site:
> http://www.mobot.org/plantscience/resbot/21EvSy.htm
> UPS and FedExpr -  MBG, 4344 Shaw Blvd, St. Louis 63110 USA
> -----Original Message-----
> From: taxacom-bounces at mailman.nhm.ku.edu
> [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Michael Heads
> Sent: Monday, December 17, 2012 2:08 AM
> To: taxacom at mailman.nhm.ku.edu
> Subject: [Taxacom] Pacific biogeography
> Dear Taxacomers,
> A few months ago we were debating Hawaiian biogeography. In a discussion
> of this topic in the book cited below, I mapped the 2000, 4000 and 5000
> m isobaths of the central Pacific. O'Grady et al. (Taxon 61: 702. 2012)
> have now suggested that this was 'disingenuous', because sea-level has
> not dropped by more than 100 m or so. But the authors overlooked the
> *1000s* of meters of subsidence that the Pacific seafloor itself has
> undergone. This is well-known to geologists and I discussed it in the
> book.
> As the seafloor has drifted away from the East Pacific Rise - the
> spreading ridge that produced it - it has cooled (increasing its
> density) over tens of millions of years and has subsided by these large
> amounts. This has led to the submergence of most of the islands that
> were perched on it.
> The current high islands are new ones. Evidence for the subsidence is
> seen in the numerous atolls of the region, formed by coral reefs which
> have grown as the seafloor subsided. The many flat-topped seamounts
> (guyots) located north, south, east and west of Hawaii are former high
> islands that were eroded to sea-level before being submerged with the
> tectonic subsidence.
> Michael Heads
> --
> Wellington, New Zealand.
> My new book: *Molecular panbiogeography of the tropics. * University of
> California Press, Berkeley.
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