[Taxacom] scientific predictions concerning Wallacean marsupials and primates

[John Grehan]

Hi Jason,

Interesting stream of thought. Some comments inserted below.

The obvious one it to ask what is meant by "normal", "observed",
"slightly", etc. All these terms are very human but very vague and I
can´t see how one cannot simply say "a little more".

The concept of dispersal is that of ecology and generally recognized as an
ecological process. Nothing vague about it in any sense that is different
from any other ecological process. And everyday the distribution of every
species changes through movement of individual organisms or their
propagules. This could be slight (just one individual seed dispersed for
example) or much more (involving movements that are almost global). True,
slight or a lot are relative, but it’s not a problem as such (at least not
for me).

“The second is the assertion that "it doesn´t lead to speciation". Not
only do I not understand exactly what is meant by this but further you
neither provide a basis to for your assertions nor examples to support
this.”

It is a conclusion reached from many analyses of allopatry. In traditional
biogeography from the time of Darwin most biogeographers have looked to
chance dispersal to explain allopatry, that allopatry is the result of
individual dispersals from centers of origin. Panbiogeography leads to a
model where dispersal (in the ecological sense) is responsible for range
expansion whereas speciation occurs locally over an already established
ancestral distribution. There are plenty of examples published in various
journal articles (all easily accessible) and in three major books. Maybe
'fonder dispersal' occurs here and there, but usually assumed (based on one
preconception or another) rather than demonstrated.

“The branch lengths within the V. indica group are much too
shallow, not just the stems but the tips as well, and the individuals
within each species have divergences which are very low compared with
other Vanessa species, which suggests a fast and very diversification,
more likely the result of recent climatic events rather than
geological ones.”

That is certainly your opinion. If there is a universal objective measuring
stick that proves that, I am interested to know.

“This exemplifies why a priori assumptions about dispersal
ability (what I suspect underpins your distinction between normal and
LD dispersal) can lead you astray and how "normal" is anything but.”

There are no a priori assumptions about dispersal ability in
panbiogeographic analysis.

“I particularly find troubling the idea that falsification is
philosophically problematic to you and that your solution is to seek
"... corroboration – either there is subsequent evidence that is in
agreement or there is not. In the latter situation one is confronted
with unresolved conflict for which there is no objective recipe to
make a choice.".

Troubling or not, this is what one is faced with when there are incongruent
findings for which there is no objective recipe to chose. That happens a
lot in science which is why there is often controversy over how to resolve
such incongruence. Sometimes there is quick resolution, sometimes there is
not. That’s life, and science.

“By rejecting all the other avenues that can possibly
test for mechanisms, your strictly orthodox interpretation of
panbiogeography has anchored the field out of science.”

Jason, you appear to be laboring under false conceptions here. There is no
rejection of any other potential avenue for testing. But any ‘tests’ are
open to challenge as to their validity which is a different matter. And one
so-called 'test' - the molecular clock divergence estimate - has been found
wanting.

“It is historical but with a bias of simply seeking to confirm what it
"knows" or create knowledge by imagining as yet unknown geological
events.”

Sorry, lost me on that. If one imagines as yet unknown geological events
(or geological structures to be more precise) based on particular
biogeographic patterns and those geological structures are later found to
exist is that not something of scientific interest? (that's rhetorical as I
acknowledge that a few years ago one or more people on Taxacom did not
consider the successes in predicting geology to be interesting).

"Odd or contradictory examples"

I’m not aware of any odd or contradictory examples in panbiogeography.
Could you specify please? Dispersalists quite often refer to 'mysterious'
or otherwise bewildering instances though.

“ labelling (calling non panbiogeographers "dispersalists" as
a way of denying vicariance to anybody but panbiogeography)”

Actually that is not correct. Vicariance biogeographers (at least some I
know) are not dispersalists.

"or simply ignored."
Examples? Be specific please. Hard to respond to generalities.

“Only when you lose that anchor can you hope for conciliatory
discourse.”

conciliatory - propitiatory, placatory, appeasing, pacifying, mollifying,
peacemaking. Not sure where you are going with that. With most people I
find I have quite amiable conversations, even when in strong disagreement.
And in fact the conversations here on TAXACOM with you and Ken and others
are very civilized and what more could one wish for in science than that?

Cheers, John


On Wed, Jun 27, 2018 at 8:53 PM, JF Mate <aphodiinaemate at gmail.com> wrote:

> Michael/John,
>
> you make a distinction of dispersal that is tailored specifically to
> make panbiogeography unassailable. You define a "normal" dispersal,
> the one that you like, as the dispersal that  "...can be observed
> every day. The distribution of every species changes (slightly) every
> day because of dispersal. ... in the weeds that colonise a garden, or
> in an albatross crossing the Pacific, and takes place by normal,
> observed means of dispersal." This distinction has several in built
> assumptions that you haven´t discussed, either because you assume them
> to be self-evident or, rather, because the distinction may not be as
> clear as you hope.
>
> The obvious one it to ask what is meant by "normal", "observed",
> "slightly", etc. All these terms are very human but very vague and I
> can´t see how one cannot simply say "a little more".
>
> The second is the assertion that "it doesn´t lead to speciation". Not
> only do I not understand exactly what is meant by this but further you
> neither provide a basis to for your assertions nor examples to support
> this. I have briefly mentioned these in the case of Polygonia
> (butterflies being a well researched group), but a much better example
> is the phylogeny of Vanessa (Wahlberg & Rubinoff, 2011) that John
> aludes to when he mentions V. vulcanica (although it is further
> removed in time). He assumes that this is an example of vicariance
> when dispersal provides a simpler explanation for lineages such as
> indica. The branch lengths within the V. indica group are much too
> shallow, not just the stems but the tips as well, and the individuals
> within each species have divergences which are very low compared with
> other Vanessa species, which suggests a fast and very diversification,
> more likely the result of recent climatic events rather than
> geological ones. In particular the placement of this clade is derived
> with respect to the basal clades (Holarctic V. atalanta and Hawaiian
> V. tamemea) and both clades sister to the Ethiopian V. abyssinica,
> which clearly suggests dispersal out of Africa, and not some
> mysterious, and much more ancient, Tethyan vicariance event.
>
> Furthermore, Wahlberg & Rubinoff find that highly vagile species have
> highly restricted sister taxa. This demonstrates that, gene flow on
> its own is not sufficient a factor to explain allopatric speciation;
> and that vagility can be highly labile. Hence current dispersal
> ability of a lineage is not in itself enough to rule out dispersal as
> a mechanism. This examplifies why a priori assumptions about dispersal
> ability (what I suspect underpins your distinction between normal and
> LD dispersal) can lead you astray and how "normal" is anything but.
>
> In regards to the Waters et al paper that Ken has kindly shared, it
> may be harsh, but your rebuttal is similar to previous answers of
> yours so it is difficult to see how it changes anything then and
> since. It is a fact that it is futile to constructively argue when any
> evidence presented by side is summarily dismissed as inherently
> tainted by their limitations while you ignore your own problems. I
> particularly find troubling the idea that falsification is
> philosophically problematic to you and that your solution is to seek
> "... corroboration – either there is subsequent evidence that is in
> agreement or there is not. In the latter situation one is confronted
> with unresolved conflict for which there is no objective recipe to
> make a choice.". By rejecting all the other avenues that can possibly
> test for mechanisms, your strictly orthodox interpretation of
> panbiogeography has anchored the field out of science. It is
> historical but with a bias of simply seeking to confirm what it
> "knows" or create knowledge by imagining as yet unknown geological
> events. Odd or contradictory examples are either fitted by a
> combination of denial (of LDD, of molecular markers,), imagination
> (lumping a few dispersal tracks and then assuming vicariance is a real
> risk), and labelling (calling non panbiogeographers "dispersalists" as
> a way of denying vicariance to anybody but panbiogeography); or simply
> ignored. Only when you lose that anchor can you hope for conciliatory
> discourse.
>
> Jason
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