[Taxacom] Pacific biogeography

[John Grehan]

'cautious rejection'?

On Mon, Dec 17, 2012 at 4:46 PM, JF Mate <aphodiinaemate at gmail.com> wrote:

> 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
> specific critique.
>
> Best
>
> Jason
>
> 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?
> >>
> >> Jason
> >>
> >> 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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> >>
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