[Taxacom] more on iguanas

Wed Dec 1 18:50:48 CST 2021

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
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> -----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.