[Taxacom] another biogeographic note for those interested

Wed Nov 30 21:59:18 CST 2016

>Vicariance does not impose this kind of contradiction<
I think "contradiction" is way too strong a word (actually, it is incorrect, there is no "contradiction"!)

>it's not just one island or archipelago that is involved in each taxon, but sometimes several<
But couldn't a species disperse from island to island?

My explanation for why each satellite only has one species is that it is small and has moved further away from the center subsequent to the dispersal event, making further dispersal harder and harder.

Stephen

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

 Subject: Re: [Taxacom] another biogeographic note for those interested
 To: "Stephen Thorpe" <stephen_thorpe at yahoo.co.nz>
 Cc: "taxacom" <taxacom at mailman.nhm.ku.edu>
 Received: Thursday, 1 December, 2016, 4:49 PM

 One could
 indeed invoke any kind of dispersal, but again one would
 have to invoke great distances and yet only in ways that
 precluded overlap other than the single center of sympatry.
 Vicariance does not impose this kind of contradiction. And
 with respect to 'satellites' it's not just one
 island or archipelago that is involved in each taxon, but
 sometimes several. So again, one requires that dispersal
 went off in different directions for each taxon, went a very
 long way (sometimes halfway across the Pacific) and to
 multiple islands, but somehow not the same islands as the
 other taxa.
 John
 Grehan
 On Wed, Nov 30, 2016 at
 10:41 PM, Stephen Thorpe <stephen_thorpe at yahoo.co.nz>
 wrote:
 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

 ------------------------------ --------------

 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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