[Taxacom] Chile-New Zealand distributions (rafting as a rare alternative)

buyck at mnhn.fr buyck at mnhn.fr
Mon Jul 26 05:52:54 CDT 2010


Dear taxacom-botanists,

There is one element missing in the discussion of Nothofagus and it  
seems very essential to me : Nothofagus is an obligatory symbiotic  
tree with specific terrestrial, ectomycorrhizal fungi. Seed dispersal  
over long distances may have happened and even germination, but  
subsequent development of the plant is very unlikely without the  
specific fungal symbionts being present. You can not discuss the  
dispersal of a symbiosis and completely ignore the evolutionary  
history of (one or more of) the implicated partner(s).
One publication that briefly discusses this element is
Pirozynski KA. 1983. Pacific Mycogeography: an appraisal. Australian.  
Journal of Botany Supplementary Series 10: 137–159

bart

Quoting Michael Heads <michael.heads at yahoo.com>:

>
>
>
>
>
> Dear Taxacomers,
>  
> Geologists often cite the 'principle of multiple working hypotheses'  
> (Chamberlin, T.C., 1890. reprinted 1965. Science 148, 754-759). This  
> holds that it is dangerous in science to have just a single  
> explanation for a phenomenon. The idea of chance dispersal is  
> popular and can explain any distribution, for example Nothofagus  
> could have dispersed from Chile to New Zealand, or vice versa, or  
> dispersed to its current range from Kalamazoo and gone extinct  
> there, etc.  Different clades in any biogeographic pattern, such as  
> the New Zealand - Chile disjunction, show differing degrees of  
> evolution. Under the evolutionary clock model that has become very  
> popular they all evolved at different times. The clock  
> model suggests that all speciation is by dispersal, none by  
> vicariance.    
>  
> As an alternative, the vicariance model looks outside the group  
> rather than within it, and assumes that different groups will evolve  
> to different extents at a given biogeographic break because of  
> different prior genome architcture. It stresses that Nothofagus  
> (Nothofagaceae) is basal in the world-wide group Fagales and that it  
> is the only member endemic to Australasia - Patagonia (fossils in  
> Antarctica). Instead of a local center of origin this model  
> proposes a world-wide ancestral Fagales. The first split is between  
> Nothofagus, which develops more or less in its current range, and  
> the rest of the families, which differentiate everywhere else. In  
> this model Nothofagus does not have a centre of origin and does not  
> disperse.
>  
> There is a complication because the northern Fagaceae overlap with  
> Nothofagus in New Guinea (N. is at higher altitude) and the mainly  
> central Australian Casuarinaceae overlap with N. in eastern  
> Australia and New Caledonia, with a couple of species also in New  
> Guinea. This can be accounted for by local range expansion of one or  
> more of the families by the normal, observed means of dispersal, and  
> is in contrast to the dispersal model which proposes extraordinary,  
> long distance transoceanic dispersal in Nothofagus by means of  
> dispersal that have never actually been observed, despite years of  
> intensive ecological research. 
>  
> A vicariance model accounts simply for the absence of Nothofagus in  
> the mountains of Borneo, central Asia, the northern Andes etc. and  
> the absence of Fagaceae etc. in New Zealand and Patagonia. A  
> dispersal model has to bring in extra ad hoc hypotheses to explain  
> these.    
>  
> Nothofagus is (a) a large tree (b) dominant over large areas and (c)  
> is wind-pollinated, producing vast amounts of pollen. Not  
> surprisingly it has a good fossil pollen record and all four extant  
> subgenera are known from the Cretaceous. Countless other groups with  
> a very similar distributions can be explained by vicariance  
> occurring at similar phylogenetic/biogeographic breaks (nodes), e.g.  
> the Hebe complex (Orobanchaceae) with individual species (!) such as  
> H. elliptica and H. salicifolia restricted to New Zealand and  
> Patagonia. Most of these are much smaller, insect-pollinated plants  
> that are not nearly as abundant as Nothofagus, and it is not  
> surprising that they have virtually no fossil record.  
>  
> Michael Heads   
>
> Wellington, New Zealand.
>
> My papers on biogeography are at: http://tiny.cc/RiUE0
>
> --- On Mon, 26/7/10, Stephen Thorpe <stephen_thorpe at yahoo.co.nz> wrote:
>
>
> From: Stephen Thorpe <stephen_thorpe at yahoo.co.nz>
> Subject: Re: [Taxacom] Chile-New Zealand distributions (rafting as a  
>  rare alternative)
> To: "Kenneth Kinman" <kennethkinman at webtv.net>
> Cc: taxacom at mailman.nhm.ku.edu
> Received: Monday, 26 July, 2010, 3:53 PM
>
>
> well I'm not suggesting that it is to be "explained" by magic or "divine
> intervention" - it is "unusual" only in the sense that I don't think  
>  there are
> any other species of beetle (or even terrestrial lifeforms of any kind) whose
> native distribution is N.Z. + Chile only ... plenty of higher taxa, but not
> species ...
>
>
>
>
> ________________________________
> From: Kenneth Kinman <kennethkinman at webtv.net>
> To: stephen_thorpe at yahoo.co.nz
> Cc: taxacom at mailman.nhm.ku.edu
> Sent: Mon, 26 July, 2010 3:38:08 PM
> Subject: Re: [Taxacom] Chile-New Zealand distributions (rafting as a rare
> alternative)
>
> Hi Stephen,
>       Whether these weevils took the long route (around Antarctica) or
> rafted directly on a Nothofagus tree, or even took the longer route
> around Antarctica in the opposite direction, the MAIN point is that
> there are several explanations that explain such a seemingly "curious"
> distribution.  Which one is the best supported remains to be seen, but I
> don't find any of them particularly curious or unusual.  That R.
> tenuirostris is pretty much identical in Chile and New Zealand would
> make me lean more toward a rafting hypothesis.     
>                     ----------Ken           
> --------------------------------------------------------
>
>
>      
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