[Taxacom] more on iguanas

[kotatsu at fripost.org]

"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!