[Taxacom] another biogeographic note for those interested

[Stephen Thorpe]

John,
Why can't dispersal go in both directions? If the "center of sympatry" is a big area, whereas the satellites are small areas, then dispersal back from a satellite to the center is more likely than dispersal in the other direction of more than one species to any one small satellite. So we could start with one species in the center which disperses to each of the satellites independently, speciates on each satellite, and then each new species disperses back to the center creating sympatry at the center. If this is combined with tectonic events causing the distance between center and satellites to increase over time, then it will become less likely that any species which disperses back to the center will be able to subsequently disperse to another satellite, maintaining allopatry between satellites.
Stephen

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On Thu, 1/12/16, John Grehan <calabar.john at gmail.com> wrote:

 Subject: [Taxacom] another biogeographic note for those interested
 To: "taxacom" <taxacom at mailman.nhm.ku.edu>
 Received: Thursday, 1 December, 2016, 4:22 PM
 
 Star vicariance represents a
 significant biogeographic pattern and process
 that is either generally overlooked, or explained away as
 dispersal from a
 common center of origin. Star vicariance is exemplified by a
 pattern of
 distributions that are largely or entirely allopatric except
 for a common
 center of sympatry, giving the appearance of a multipoint
 star (depending
 on the number of taxa involved).
 
 
 Dispersal explanations attribute the region of sympatry as a
 center of
 origin from which each of the taxa spread out. The problem
 with this view
 is that it does not explain why each taxon managed to spread
 so far and
 wide and yet keep out of each other’s ‘territory’
 other than the region of
 sympatry. Vicariance does not impose this quandary, but
 recognizes that the
 allopatry is the result of vicariance of a multitude of taxa
 that
 subsequently underwent local dispersal resulting in sympatry
 in a
 relatively localized area. Sympatry is effectively evidence
 of dispersal.
 
 
  In “Biogeography and Evolution in New Zealand” Heads
 draws attention to
 star vicariance with respect to several taxa, including a
 very nice example
 in the plant genus Astelia which has two main clades around
 the Indian and
 Pacific basins respectively. The Pacific group forms a star
 pattern with
 New Zealand at the center. Even though the overlap of
 individual ranges
 looks complex against present day geography, it is possible
 to offer
 reconstructions of the possible ancestral range of each
 member group prior
 to the dispersal that led to the present day overlap.
 
 
 Even though the examples are presented for New Zealand, the
 star pattern
 could apply to any region of the globe and as such should be
 a pattern that
 any student of biogeography could recognize. At the very
 least it would not
 be unreasonable for recognition of star vicariance to be a
 standard exam
 question for graduate students (or any students for that
 matter). I’m have
 not seen star vicariance presented in any university
 biogeography text
 book, but admittedly I have not read every one that is out
 there. However,
 it goes without saying that “Biogeography and Evolution in
 New Zealand”
 should be considered as a standard university text book for
 any
 biogeography course anywhere.
 
 
 John Grehan
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