[Taxacom] What is possible or not in biogeography

[Stephen Thorpe]

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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