[Taxacom] Pacific biogeography
aphodiinaemate at gmail.com
Mon Dec 17 15:46:10 CST 2012
As I said John, ocean floor subsidence is generally well known (as are
plate tectonics). Cautious rejection of panbiogeography does not imply
ignorance of geology, simply the acknowledgement that biogeographical
patterns are a complex interplay of various mechanisms. What I want to
know is if Michael´s email is in reference to anything other than a
P.S: By "our" I mean humanity.
On 17 December 2012 22:29, John Grehan <calabar.john at gmail.com> wrote:
> The trouble with 'our' (whoever that is) improved understanding is that it
> does not always appear to be consistently understood. I think the point
> about the subsidence is that one cannot assume current topographic
> elevations as unchanging and make biogeographic assertions on that basis -
> which is what the critics appear to have done.
> John Grehan
> On Mon, Dec 17, 2012 at 4:01 PM, JF Mate <aphodiinaemate at gmail.com> wrote:
>> The email feels like it was meant for someone else. Although our
>> improved understanding of the geological history of the Pacific has
>> helped to solve some problems (i.e. taxa older than the islands they
>> currently inhabit) it is not very clear to me how seafloor subsidence
>> (a well known phenomenon BTW) would significantly alter the
>> biogeographical status quo or how this can be invoked to support
>> panbiogeographical theories. Any ideas?
>> On 17 December 2012 09:07, Michael Heads <m.j.heads at gmail.com> wrote:
>> > 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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