[Taxacom] Long-distance oceanic dispersal (rafting) of Nothofagus species

[Kenneth Kinman]

Hi Jason,

       Excellent post.  Regarding Michael's "why only once" argument, I would only add that I have provided another explanation in a post back in 2012.  Namely: competitive exclusion, where the first dispersal is so successful that it fills all the niches for that animal or plant.  If another dispersal happens millions of years later, they usually can't compete with the already well-established populations of its relative.

      Here is a quote from the end of my posting on 01 January 2012:

"In view of John's criticisms, it should be remembered that dispersal ability certainly does not ensure that oceanic dispersals will be successful in most cases. Being able to disperse long distances is only the first step, but lack of suitable habitat, and more importantly competitive exclusion by other taxa already well-established, are obviously barriers to even good dispersers being automatically spread geographically. Such arguments against dispersalist hypotheses are therefore unconvincing (perhaps simple, but perhaps too often simplistic)."

Here's a weblink to that post: http://mailman.nhm.ku.edu/pipermail/taxacom/2012-January/121575.html


-------------Ken


________________________________
From: Taxacom <taxacom-bounces at mailman.nhm.ku.edu> on behalf of JF Mate <aphodiinaemate at gmail.com>
Sent: Wednesday, June 6, 2018 11:23 AM
To: Taxacom
Subject: Re: [Taxacom] Long-distance oceanic dispersal (rafting) of Nothofagus species

John,

analyzing biogeographic distributions is not very useful in the
absence of a time scale. Timing is often the only difference between
dispersal and vicariance, and all the arguments I can recall revolve
around the absolute or relative timing of splits of one lineage vs
another and/vs tectonics. That is why I think you focus so much on the
only proxy we have to complete the extremely patchy fossil record.
In the particular case of the Platyrrhini, the available evidence
suggests that the age for the group is c. 25-32mya
(https://doi.org/10.1093/molbev/msg172) and this is the most widely
accepted date (give or take but close to this range) using well
accepted molecular dating methods and fossils. You can quibble about
fossils and calibrations if the window was small enough, but the gap
is a chasm considering what you would need for the alternate scenario,
so we can only conclude, based on the available evidence at hand, that
the NW monkeys arrived there over sea and not as a result of
vicariance. Should fossils be found at a later date that push the
origin back sufficiently to consider the latter scenario then great,
but so far this is not the case. If they made it there swimming,
rafting or island-hopping (all three possible perfectably reasonable
dispersal mechanisms) is a matter of testing the ability of these
monkeys to survive each of these scenarios. None of this is a fairy
tale, pseudoscience nor an attack on vicariance.

This sort of dovetails with Michael´s often repeated question of "why
only once". My answer is because dispersal is hard, unplanned and the
chances of success slim to nil.


Jason




On 5 June 2018 at 01:00, John Grehan <calabar.john at gmail.com> wrote:
> Jason,
>
> I would suggest that the snag is not so much one side claims that molecular
> data is glorified phenetics or that dispersal is an unquantified, undefined
> amount that exists beyond the equally fuzzy "ecological dispersal". In the
> present discussion the issue has revolved around the age of extant
> Nothofagus and monkeys. In both cases the challenge presented to their being
> young was to ask for evidence. So far the response has been fossils, but
> without explaining how the present fossil record precludes Mesozoic origins
> for the taxa. There has further been the assumption that molecular dates are
> actual or absolute rather than minimal, but Ken says this is a red herring,
> I think because he was indicating that his position was not based on
> molecular divergence estimates (I may have that wrong in which Ken can
> correct).
>
> Arguments about molecular data and trees are phenetic or not is of no
> concern as far as biogeographic analysis is concerned - which can analyze
> the geographic distribution of any phylogeny.
>
> John Grehan
>
> On Mon, Jun 4, 2018 at 4:42 PM, JF Mate <aphodiinaemate at gmail.com> wrote:
>>
>> What I meant is that the topic, as far as I see it, is dead in Taxacom
>> (bar a few brave souls) since no fruitful debate is possible. The
>> discourse invariably hits the same snags:
>>
>> One side claims that molecular data is glorified phenetics with no
>> contextual value if it contradicts a particular point of
>> view/hypothesis.
>> Dispersal is an unquantified, undefined amount that exists beyond the
>> equally fuzzy "ecological dispersal".
>> More fossils can always be found.
>>
>> As for the field, what I see is that people have long moved on,
>> pursuing a hybrid model where the facts, always scarce and patchy, may
>> support one model or another, and where novel data may refute previous
>> hypotheses. In the end some things have moved (either due to luck or
>> ability) and others haven´t, but in the end every case should assume
>> that there is no de facto explanation.
>>
>> Jason
>>