[Taxacom] Dispersal example

[Michael Heads]

Hi Fred,

Your founder-takes-all model would be a very good explanation for the
common arrangement of simple allopatry, and it has recently been promoted
by Waters et al. (2013 in TREE). But it doesn't account for another very
common pattern that can be illustrated by New Zealand groups such as the
plants Hebe, Olearia and Astelia. These groups comprise several clades,
each in New Zealand and one other area, e.g. NZ + SE Australia, NZ + New
Guinea, NZ + New Caledonia, NZ + Fiji, NZ + Tahiti, NZ + Chile.

In this 'star pattern' there are two main aspects to explain: (1) the high
level of allopatry of the clades, and (2) their overlap in NZ. The
founder-takes-all (competition) model  explains the allopatry, but it is
inconsistent with the overlap in NZ. I think the pattern is the result of a
widespread ancestor, followed by vicariance around a break in NZ, followed
by local overlap in NZ. If the stages in the process are mediated by
tectonics, for example, rather than chance dispersal, this would explain
why the pattern is repeated in different groups.

Michael


On Tue, Apr 15, 2014 at 7:15 AM, Fred Schueler <bckcdb at istar.ca> wrote:

> On 4/14/2014 1:17 PM, John Grehan wrote:
>
> > I think it is less a case of considering long-distance dispersal as
> > unlikely and ask why it did not occur twice, but rather why did it occur
> > just once, time and time again for group after group...
>
> * as the old Irish bards used to say: "Not difficult." Once the group is
> established, a second colonization is made unlikely by the presence of
> the established populations of the taxon.
>
> fred.
> ------------------------------------------------------------
>           Frederick W. Schueler & Aleta Karstad
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>
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-- 
Dunedin, New Zealand.

My recent books:

*Molecular panbiogeography of the tropics.* 2012. University of California
Press, Berkeley. www.ucpress.edu/book.php?isbn=9780520271968

*Biogeography of Australasia:  A molecular analysis*. 2014. Cambridge
University Press, Cambridge. www.cambridge.org/9781107041028