[Taxacom] more on iguanas

[John Grehan]

Hi Rich. What you are referring to is what I would view as ordinary
ecological dispersal that is empirical (observable) and does indeed explain
range expansion and persistence. This is different from 'chance' dispersal
that is used to explain allopatric differentiation.

Cheers, John

On Wed, Dec 1, 2021 at 7:51 PM Richard Pyle via Taxacom <
taxacom at mailman.nhm.ku.edu> wrote:

> Chance dispersal is also certainly not imaginary among many/most marine
> organisms that have planktonic larval stages, even though they can swim of
> their own volition and have lifespans that may cover several years, have a
> wide range of dietary strategies, and in most cases are not attached to
> other organisms as adults (but in most cases are unable to make large-scale
> movements across vast geographical areas as adults).
>
> Aloha,
> Rich
>
> 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
> Our Mission: Bishop Museum inspires our community and visitors through the
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> environment of Hawaiʻi and the Pacific.
>
> > -----Original Message-----
> > From: Taxacom <taxacom-bounces at mailman.nhm.ku.edu> On Behalf Of
> > Daniel Gustafsson via Taxacom
> > Sent: Wednesday, December 1, 2021 2:29 PM
> > To: taxacom <taxacom at mailman.nhm.ku.edu>
> > Subject: Re: [Taxacom] more on iguanas
> >
> > "the imaginary conception of 'chance' dispersal"
> >
> > For minute, parasitic, wing-less insects that have no free-living stage,
> never
> > leave the host, cannot walk on a non-feather surface, are constantly
> under
> > threat of being killed by their host which is several orders of
> magnitude larger
> > than they are, have a life span after hatching of about a month, and of
> course
> > virtually always die when their host dies -- for these, "chance
> dispersal" (or
> > host switching) has been shown to be a major issue confounding old ideas
> > about strict co-speciation in virtually every genus that has been
> studied to any
> > extent in the last 20 years, and is uncontroversial.
> >
> > But for large, non-parasitic, animals that can walk, fly, swim etc. of
> their own
> > volition, may have life spans that cover several years, may make regular
> large-
> > scale movements across vast geographical areas, may be omnivorous or at
> > least not limited to a single kind of food, and have life stages that do
> not
> > consist of being attached to another organism -- for these chance
> dispersal is
> > imaginary.
> >
> > What a time to be alive.
> >
> > Are these repetitious, and above all non-taxonomic, discussions on
> > panbiogeography ever going to end, or is this a preview of the hell that
> all
> > taxonomists go to when we die?
> >
> >
> >
> >
> >
> >
> > > To the biogeographic hobbyists: in my opinion, the primary problem of
> > > the molecular age underestimate papers is not even so much about their
> > > misrepresentation of fossil age calibration, but the way this
> > > technique lets such authors escape from any responsibility to be
> > > familiar with biogeographic patterns in general. After all, if each
> > > individual taxon has its own history of 'chance' dispersal, then there
> > > is no need to see any connection with the biogeography of any other
> > > taxon or the possibility of tectonic correlations. In effect, an
> > > intellectual curtain is drawn over the biogeographic stage. What is
> > > not seen, does not exist. For the iguanas, for example, there seems to
> > > be no comprehension of the basic distributional facts as noted in
> > > Heads & Grehan (2021): "The Iguanidae and their sister, Agamidae (with
> > > Chamaeleonidae), are almost perfectly allopatric, and this is
> > > consistent with the origin of each clade more or less in situ, by
> > > vicariance in a global ancestor (Heads, 2014 p. 119). In this model,
> > > Iguanidae did not cross the Pacific in either direction. The origin of
> > > the trans-Pacific affinity is explained by breaks in a global ancestor
> > > at sites that correspond with the western margin of the Pacific plate.
> > > The only dispersal required in either Iguanidae or their sister group
> > > is in or around Madagascar, where the two clades overlap." I do hope
> > > the critics on Taxacom make due note of the reference to the evidence
> > > for dispersal here!
> > > But of course, it is not the imaginary conception of 'chance'
> > > dispersal,
> > > but ordinary ecological dispersal (an observable phenomenon)
> > > responsible for range expansion. The real biogeographic issue has
> > > never been about contesting vicariance against dispersal [which has
> > > generated the trite conclusion that both are involved in different
> > > taxa], but coming to an understanding about how the two processes are
> > > interrelated in the evolution of distributions. Croizat's work was, in
> > > my opinion, the first substantial effort to accomplish that - by
> > > making reference to the by far greatest biodiversity resource
> > > available - the distributions of animal and plant taxa that are made
> > > evident through the combined sciences of taxonomy, systematics, and
> > > geography.
> > >
> > > As for my characterizations sometimes being seen to be 'over the top',
> > > I suppose they might be. Perhaps from now on I will just refer to such
> > > papers as 'really, really, really terrible'. Hope that will be a
> > > widely acceptable expression of an opinion. And of course always, with
> > > reference to why that opinion is reached, since how one reaches an
> > > opinion in science is more important than the opinion itself.
> > >
> > > Interesting that those who are so outraged by language are evidently
> > > not able to come to the table with responses to questions about their
> > > assertions (as in recent questions by Heads). I think that says a lot.
> > >
> > > Cheers, John Grehan
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> > > Nurturing nuance while assailing ambiguity for about 34 years,
> > > 1987-2021.
> >
> > --
> > Dr. Daniel R. Gustafsson, Research Assistant Professor Institute of
> Zoology
> > Guangdong Academy of Sciences, Guangzhou, China.
> >
> > Ask me about chewing lice!
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> > Nurturing nuance while assailing ambiguity for about 34 years, 1987-2021.
>
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> Nurturing nuance while assailing ambiguity for about 34 years, 1987-2021.
>