[Taxacom] Recent transPacific rafting due to tsunami

John Grehan calabar.john at gmail.com
Mon Dec 21 13:40:24 CST 2020


What I find really interesting about Hawaii is that it provides such a
classic example of metapopulation survival of taxa within the Pacific basin
with ample geological evidence in the form of many nearby guyots and the
former movement of oceanic plateaus.  There are also many patterns of
parallel allopatric relationships involving Hawaii that make sense in terms
of former widespread ancestral distributions - such as Monarcha
flycaters (birds) and Cyrtandra (violets) to mention just two. You would
think that birds could just get about anywhere, and certainly strays often
do. But here is a bird and plant group with the same Pacific pattern of
biogeography and each having its own allopatric subclades. I know, I know,
maybe the both rafted together all over the place (pity the parrot did not
survive on the Kon Tiki).

On Mon, Dec 21, 2020 at 2:20 PM Richard Pyle <deepreef at bishopmuseum.org>
wrote:

> OK, so our disagreement is purely semantic, then.  I can live with that.
>
>
>
> Richard L. Pyle, PhD
> Senior Curator of Ichthyology | Director of XCoRE
>
> *Bernice Pauahi Bishop Museum*
>
> 1525 Bernice Street, Honolulu, HI 96817-2704
>
> Office: (808) 848-4115;  Fax: (808) 847-8252
>
> eMail: deepreef at bishopmuseum.org
>
> BishopMuseum.org <http://hbs.bishopmuseum.org/staff/pylerichard.html>
>
> *Our Mission: Bishop Museum inspires our community and visitors through
> the exploration and celebration of the extraordinary history, culture, and
> environment of Hawaiʻi and the Pacific.*
>
>
>
> *From:* John Grehan <calabar.john at gmail.com>
> *Sent:* Monday, December 21, 2020 9:04 AM
> *To:* Richard Pyle <deepreef at bishopmuseum.org>
> *Cc:* Taxacom <taxacom at mailman.nhm.ku.edu>
> *Subject:* Re: [Taxacom] Recent transPacific rafting due to tsunami
>
>
>
>
>
> Hi Rich, See below
>
> “John -- I assume your arguments apply only to larger terrestrial
> organisms, correct?”
>
> No
>
> “Those of us who work on marine organisms with planktonic larvae have
> seen plenty of evidence of "rare" dispersal events in the form of
> singletons that appear outside their range, often as juveniles.”
>
> Sure, one sees the same thing with many organisms – birds, butterflies,
> fish, snails etc.
>
> “Even in my own tiny lifetime, I've personally witnessed two cases where
> a species previously absent from a locality (based on extensive historical
> surveys) became established in large numbers. Unless they were brought by
> humans (which they weren't), then the only rational explanation is that
> they arrived by chance dispersal events.”
>
> I would see this as normal ecological dispersal where species may exist as
> metapopulations encompassing different localities, coming or going from
> individual localities. Ecological dispersal is an empirical and observable
> phenomenon by which ranges may expand or be maintained.
>
> “Hawaii is home to some of the world's highest rates of endemism among
> coral-reef fishes. Most of these species have their closest relatives
> elsewhere in the Pacific. I guess you could argue that all these species
> were at one time widely distributed with regular/frequent gene flow, and
> then only later became isolated from each other and diverged.  But that
> scenario differs from "chance dispersal" only in degree, not in kind.”
>
> The difference here is not about chance dispersal, but about ecological
> dispersal over the ancestral range which explains the range, but not
> divergence of descendants.
>
> Among those of us who study coral-reef organisms, arguments that "there is
> no evidence for chance dispersal being the mechanism for the origin of
> allopatry" sound a bit like arguments that "there is no evidence for
> evolution by natural selection", or "there is no evidence for plate
> tectonics".
>
> My challenge was for those who invoke unique chance dispersal to explain
> allopatry to provide some evidence. Instead I just get rhetoric or
> repeating of assertions.
>
> “None of us can be certain about events that purportedly happened in the
> past (gene frequencies shifting over time as a result of selection
> pressure, continents moving, rare events allowing organisms to expand their
> range then become cut off from source populations, etc.)  But at a certain
> point, it just seems silly to assume that such things did not happen.”
>
> I'm not assuming anything of the sort. The underlying issue here is that
> people repeatedly invoke one off chance events to explain allopatry without
> providing an empirical foundation. When the BM says 'we know' that monkeys
> voyaged over the Atlantic it is engaging in twaddle.
>
> Cheers,
>
>
>
> John Grehan
>
>
>
>


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