[Taxacom] What is possible or not in biogeography

[John Grehan]

Stephen,

I am sure you will be looking forward to reading Heads' books at your
earliest opportunity.

John Grehan

On Wed, Dec 21, 2016 at 7:16 PM, Stephen Thorpe <stephen_thorpe at yahoo.co.nz>
wrote:

> Well, perhaps we have a mixture of vicariance followed by dispersal
> resulting in scattered new species. The N.Z. species (M. sinclairii) is
> only known from the Three Kings Island and the disjunct Hen and Chickens
> Islands, and the explanation for this is controversial, with one theory
> being translocation by Maori from Three Kings to Hen & Chicks. However,
> seed dispersal by birds (if a rare event, or at least rare that seed lands
> in a suitable spot) could explain it (some birds may favour small islands
> for nesting, even in pre-European times). The distribution also looks less
> unusual when one considers the other species of the genus in the Pacific,
> which are also very scattered and disjunct on small islands. Who knows, but
> my mind is open. I'm not sure how many other Fiji-New Zealand relationships
> there are which exclude New Caledonia?
>
> Stephen
>
> --------------------------------------------
> On Thu, 22/12/16, John Grehan <calabar.john at gmail.com> wrote:
>
>  Subject: [Taxacom] What is possible or not in biogeography
>  To: "taxacom" <taxacom at mailman.nhm.ku.edu>
>  Received: Thursday, 22 December, 2016, 12:39 PM
>
>  Following the recent posting on
>  biogeography an earnest colleague on
>  TAXACOM contacted me off list to ‘suggest’ that the
>  genus *Meryta* a is a
>  good example of a distribution which cannot be explained
>  other than by
>  dispersal of seeds by birds. Unfortunately he could not
>  provide any
>  analytical evidence and could only assert that “the
>  species are so disjunct
>  and scattered”. This brings forward the point that in
>  analytical
>  biogeography there is no presumption about theorized
>  dispersability or
>  distinction over the extent of disjunction or scattering of
>  taxa. While my
>  colleague personally felt that bird dispersal was the only
>  possibility,
>  this does not mean that is necessarily so.
>
>
>  Biogeographic analysis shows that allopatry, both within the
>  genus and with
>  respect to potential relatives, is predominant and that the
>  distribution of
>  *Meryta* is representative of many other taxa in the region.
>  Bird mediated
>  dispersal of seeds may explain ecological survival, but not
>  the geography
>  of differentiation (at least not without creating
>  paradoxes). Below is the
>  excerpt from Heads (2012):
>
>
>  "Trees in the genus *Meryta *are distributed from Micronesia
>  (Yap) to
>  south-eastern Polynesia (Lowry, 1988; Fig. 6-13). The two
>  main clades in
>  the genus (not mapped here) are allopatric; on is only in
>  Fiji and New
>  Zealand, the other widespread in the central Pacific
>  (Micronesia, New
>  Caledonia, Vanuatu, and southern Polynesia). Tronchet et al.
>  (2005)
>  accepted that the break between the two clades represent
>  “ancient
>  vicariance.”
>
>
>  Possible relatives of *Meryta* include a clade termed
>  “Melanesian
>  *Schefflera*” (including *Plerandra, Dizygotheca*,
>  Gabriellae group, etc.)
>  (Plunkett et al., 2005; Plunkett and Lowry, 2007; Fig.
>  6-13). The two
>  clades are largely vicariant, with a region of overlap: New
>  Caledonia,
>  Vanuatu, and Fiji. Both clades have most of their diversity
>  in New
>  Caledonia, which could be the result of the composite
>  tectonic structure of
>  the island. *Pseudopanax* of New Zealand is another
>  relative, and the three
>  groups may form a south-west Pacific clade (G. Plunkett,
>  pers. comm.).
>  Another possibility is that “Melanesian *Schefflera*,”
>  *Meryta*, and then
>  *Pseudopanax* are the three basal branches in a widespread
>  Indo-Pacific
>  group, with the main, widespread clade being *Polyscias
>  *s.lat (not shown)
>  (Plunkett and Lowry, 2010). In any case, *Meryta *is a
>  distinctive genus
>  and a typical central Pacific group.”
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>  Injecting Intellectual Liquidity for 29 years.
>
>