[Taxacom] Dispersal... again

[Weakley, Alan S]

I suspect that the Illinois - Australia situation that Dick is remembering uncertainly is the generic distribution of the mycotrophic Thismia (Thismiaceae), which is tropical (not strictly Australian) and found once, apparently a different (and presumed extinct) species, Thismia americana, in a prairie in the Chicago area in the USA.

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Michael Heads
Sent: Tuesday, October 25, 2011 10:01 PM
To: Dick Jensen
Cc: taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] Dispersal... again

Hi Dick,
?
My own experience is that geographic patterns can be explained with?phases of range expansion (by normal dispersal, using normal means seen every day, and not?involving?differentiation) alternating with?phases of vicariance. There is no need for a separate process of 'chance dispersal', at least for the usual patterns, but maybe it would explain genuine, one-off distributions. My first question would be: is the Australia - Illinois plant really a one-off or is there a shared pattern? (it rings a bell - is it a Cuscuta or something?). For rare distribution patterns you have to look widely, to invertebrates for example. Other questions that can be investigated: are the Australian and Illinois populations differentiated? Where are?the sister group and other relatives? Perhaps the group is a?relict?of a Tethyan distribution -?there are heaps of Australasia - Mediterranean disjunctions.????
?
Michael

Wellington, New Zealand.


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


________________________________
From: Dick Jensen <rjensen at saintmarys.edu>
To: John Grehan <jgrehan at sciencebuff.org>
Cc: taxacom at mailman.nhm.ku.edu
Sent: Wednesday, 26 October 2011 2:26 PM
Subject: Re: [Taxacom] Dispersal... again



Does dispersal ever play a role in understanding geographic patterns?? This should be a simple yes/no question because there must be some patterns that are most readily (and scientifically) explained by dispersal.? I recall, from years ago, hearing a report of a plant species (I don't recall what it was) that was known to occur in two places in the world - Australia (where it was common)?and Cook County, Illinois (where it was quite rare).? The only logical explanation was long-distance dispersal.? How else? 



Dick J 






From: "John Grehan" <jgrehan at sciencebuff.org>
To: taxacom at mailman.nhm.ku.edu
Sent: Tuesday, October 25, 2011 9:10:15 PM
Subject: Re: [Taxacom] Dispersal... again 

To my way of thinking the 'endless' discussion is not about vicariance vs dispersal, but about the assumptions that most biogeographers have, and continue to make about using Darwin's theory of center of origin and means of dispersal to understand the spatial structure of life rather than analyzing the spatial structure of life to derive an understanding about the role of means of dispersal in the origin of geographic differentiation. 

To play the worn our record again, dispersal is very popular among biogeographers because most biogeographers are not interested in analyzing the spatial structure of differentiated entities and getting to know the tedious details of distribution (tedious because they are so often repetitive). With centers of origin and dispersal one is freed up from reading the records of life to make up whatever center of origin and dispersal story for an individual group or situation without having to worry about those nagging spatial incongruities. 

John Grehan 

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Frederick W. Schueler
Sent: Tuesday, October 25, 2011 4:18 PM
To: taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] Dispersal... again 

On 10/25/2011 3:47 PM, Michael Heads wrote: 
> 
> You wrote: '...vicariance (allopatry in Mayr?s parlance...'. ?For Mayr, allopatry was not caused by vicariance, but by chance dispersal. 

* sometimes it was, and sometimes it wasn't - reread "Animal Species and Evolution." 

This endless vicariance versus dispersal discussion reminds me of the "are populations regulated density dependently or density-independently?" controversy of the 1960s which, faded away when it turned out that sometimes they were, and sometimes they weren't. 

fred schueler. 
------------------------------------------------------------
?? ? ? ? ?Frederick W. Schueler & Aleta Karstad Bishops Mills Natural History Centre - http://pinicola.ca/bmnhc.htm Mudpuppy Night in Oxford Mills - http://pinicola.ca/mudpup1.htm Daily Paintings - http://karstaddailypaintings.blogspot.com/
?? ? RR#2 Bishops Mills, Ontario, Canada K0G 1T0
?? on the Smiths Falls Limestone Plain 44* 52'N 75* 42'W
?? ?(613)258-3107 <bckcdb at istar.ca> http://pinicola.ca/
------------------------------------------------------------
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