[Taxacom] Dispersal... again

[Michael Heads]

Hi Ken,
?
My comments are inserted below.
?
Michael

Wellington, New Zealand.


My papers on biogeography are at: http://tiny.cc/RiUE0


________________________________

From: Kenneth Kinman <kennethkinman at webtv.net>
To: taxacom at mailman.nhm.ku.edu
Sent: Sunday, 30 October 2011 4:44 PM
Subject: Re: [Taxacom] Dispersal... again


Michael,? ? 
? ? ?  I am not sure Mayr would have restricted vicariance just to the
Pleistocene, even in the 1940s, and certainly not once plate tectonics
starting taking hold in the 1950s and 1960s.? 

MH: See for example,?Mayr and Diamond 2001 'The birds of northern Melanesia: speciation, ecology, and biogeography'. This is a huge study of biogeography, but no mention of any geology prior to the Pleistocene. They attribute the entire bird?fauna to?dispersal and vicariance due to?Pleistocene sea-level change.

And your suggestion that
"many authors" still use such a model seems unbelievable to me (who are
some these "many authors" to which you refer?).? ? ? ? ? ? ? ? 

MH: Any issue of Journal of Biogeography, Systematic Biology, Molecular Phylogenetics and Evolution etc. have studies using centers of origin/dispersal models, with Pleistocene vicariance.

?????? In any case, as evidence for plate tectonics and continental
drift accumulated, Mayr accepted more cases of vicariance, such as when
it became clear that North America and Europe were connected relatively
late in time? (compared to the drift of South America from Africa).? ? ? ? ? ? 

MH: Where did he cite a pre-Pleistocene vicariance explanation for North American biota?

??????? However, I think he would agree that the pendulum has swung too
far in the other direction, 

MH: Of coure, he definitely would. He didn't like any pre-Pleistocene vicariance.

and that some pangeographers have overshot
the mark 

MH: Yes, he definitely didn't like pangeography.

and began proposing vicariance hypotheses far too much, so much
so that when long-distance dispersal evidence is presented, such
panbiogeographers seem to automatically object (in what I call a
knee-jerk reaction), and over exaggerate problems with molecular clocks
and the fossil record.?

MH: The problems with the fossil record and fossil-calibrated molecular clocks are profound.?An uncritical acceptance of that data has been a disaster?for?biogeography.??Look at the recent attempt to introduce Bayesian methods. Authors?attribute exponential priors to the fossil dates, i.e. the maximum probability of the clade age is the same as (!) the fossil age, and earlier ages have rapidly (exponentially) decreasing probabilites.?There is no justification at all for this assumption, it's not based on any data or analysis, just the 'expert' views of the authors. These priors will?give you, following analysis of the phylogeny,?a nice small range for clade age *with statistical support* (age usually expressed as a 95% highest posterior density interval, i..e. credibility interval).?It's completely? bogus, and yet it's now infested all the journals.??????

?John Grehan in particular seems to exaggerate
problems with molecular clocks and suggesting long fossil gaps, even
when such exaggerations stretch credulity (as in the case where he
objects to Nile crocodiles dispersing across the Atlantic).? ? 

MH: There is?no evidence?for?crocodiles dispersing across the Atlantic (unless oldest fossil ages are treated as?clade ages, which is unjustified). But there is?plenty of good biogeographic evidence suggesting the trans-Atlantic break was due to?Early Cretaceous rifting in the Atlantic.?The genus Crocodylus is pantropical and the Old World clades include a group: Australia (New Guinea (Philippines)), more or less east of Wallaces Line. This break is?often acknowledged (not by you, I know) as reflecting tectonics (Makassar Strait is an Eocene feature). The direct Philippines - New Guinea disjunction (not involving the Moluccas)?is a standard one (Mearnsia bird, Mearnsia plant) and can be related to?earlier Cenozoic terrane accretion. The Indian mugger crocodile has distribution limits very close to the plate boundary in the east (Pakistan) and west (Burma). Among the American species, the Cuban one, C. rhombifer?is basal. Antillean groups are
 often basal to diverse mainland American groups, rather than nested in them, and?this?common pattern is?not?predicted in a dispersal model. Instead it can be related simply to the formation of the Caribbean basin (Cretaceous). This fits nicely with the next basal clade, endemic to the?Atlantic?(i.e. cratonic) part of Mexico (C. moreletii). The primary?biogeographic split in Mexico is not a north/south one, as Wallace proposed,?but east/west, and relates to the Cretaceous tectonics of the Guerrero terrane (the western half of the country).?The next clade (C. acutus) is in?western Mexico (Guerrero etc.),?Antilles,?southern Florida, central America, western Colombia and northern Colombia/Venezuela.?In Colombia,?the distributions appear to be?pre-Andean (e.g. isolated records of C. acutus on the 'wrong' side of the Central Cordillera, in the upper Magdalena Valley). ?The sister of acutus, the last species, is in the Orinoco. The last two
 species have split at the?Cretaceous break between the accreted terranes of western Colombia and the Caribbean on one hand, and cratonic South America on the other. Why is Crocodylus and crocodylids?in general, widespread in western Colombia but absent from eastern,?Amazonian (cratonic) Colombia??In fact they are represented there, as their sister group, alligators,?are?there with diverse species of?Caiman,?Palaeosuchus, and Melanosuchus. Again, the whole pattern fits very neatly together from species up to genus and even family. The rise of the Andes began in the Cretaceous and the main effect on lowland groups will have been the?first emergence from the sea (rather than the Cenozoic?phase that produced the great altitudes). 

If the trans-Atlantic break was due to rifting, the chronology would fit very simply indeed with all these breaks.??Alternatively, the entire pattern could be due to chance dispersal, and all the correlations of phylogenetic breaks with?bounding faults of plates and terranes?could be?entirely coincidental.????


?????? And selectively bashing Mayr for what he wrote in the 1940s
(before plate tectonics was well documented or understood) seems like a
cheap shot.? 

MH: See his 2001 book with Diamond on 'northern Melanesia' (it's?actually on the Solomons and the Bismarcks). It concerns the avifauna of a plate margin, the most important tectonic feature there is, and yet this?fact is never mentioned,?let alone factored?into the analysis. Mayr's work from the 40s through to the early 2000s was?tremendously influential and any biogeographer has to engage with it. It's impossible to overstate its influence. For example, it led directly to?'Island Biogeography', the single most cited work in biogeography. 

The avian fauna of Australasia is no doubt more a result of vicariance than was realized back in the 1940s, 

MH: Hooker and Huxley had the biogeography?well-worked out in the 19th century and supported vicariance.? 

but that is no reason to now minimize the evidence of dispersal either.? I really hate it when
the pendulum swings too far in the opposite direction (or present-day
researchers overly criticizing what was published over 60 years ago).?

MH: How about 'under criticising' it or even just?swallowing it - hook, line and sinker - simply because they were taught it in first year?
???????
?
?????? Anyway, I feel more comfortable criticizing John Grehan in some
of his present-day knee-jerk reactions than trying to retroactively
criticizing Mayr for being conservative in what aspects of plate
tectonics he accepted as evidence accumulated during the 1940s through
1960s.

MH: It doesn't really have anything to do with plate tectonics, it's the center of origin/dispersal model for speciation that's the problem. Hooker and Huxley didn't know about plate tectonics, but they made very important?progress in biogeography. This was?because, to a large extent, they ditched the center of origin/dispersal paradigm and accepted vicariance, not?movement,?as the model for speciation.? 
????
????? Most importantly, that vicariance was underestimated during the
1940s is no excuse for overestimating vicariance in the present.? It
sort of reminds me of the paraphyly debate.? The problems caused by
excessive paraphyly in classifications was also underestimated during
the middle of the 20th Century, but the excessive pendulum swing toward
strict cladism is far more problematic (even more so than the
vicariance-dispersal pendulum under discussion).? I really hate such
pendulum swings when they go to far in either direction.?

MH: Obviously that's not good, by definition. But what's too far? In my opinion, it's often when 100% of the people support one model, e.g. accepting that a paraphyletic basal grade is a center of origin. ?An area phylogeny A (A (A (A (B)))) is *always* (I'd like to be proved wrong) accepted as a center of origin in A, followed by dispersal to B. ?



????
?????????????? -----------Ken Kinman? ? ? ? ? ? ? 
----------------------------------------------------------? ? ? 

Jason wrote:
????? Please tell me how vicariance is not mentioned, in equal footing,
in this quote. (for those interested the article can be found in this
link
http://elibrary.unm.edu/sora/Auk/v099n03/p0616-p0622.pdf)

Michael Heads responded:? 
? ? ? Of course it is?mentioned. But?Mayr's?center of
origin/dispersal analyses (and Pleistocene vicariance) were?the
standard model for biogeography since the 1940s and for many authors
still are. In the quote above,?Joseph?bemoaned?the effect that
Mayr's work?had had on Australian ornithology, but Mayr's work had?a

similar influence?in many other parts of the world. Whether a
biogeographer was working on the fauna of?Winneba or Wewak, he or
she?was?supposed?to study the?'colonization' of the
area.??Evidently, it was untenable and not worthy of discussion to
think that birds could have been in Australia all along?. 



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