[Taxacom] Nothofagus (Chile-New Zealand distributions)
michael.heads at yahoo.com
Tue Jul 27 02:00:14 CDT 2010
Dear Ken and colleagues,
If Nothofagus really were such a good disperser (thousands of miles across open ocean when its seeds are intolerant of seawater) how could we explain the fact that it has not migrated to Borneo, Asia etc. or along the Andes, as this would be so much easier? It survives in sympatry with Fagaceae in New Guinea (occurring at higher altitude) so why not in the central and northern Andes, Borneo etc.? There seems no need for special, long distance dispersal events which do not fit with its known dispersal ecology (or its mycorrhiza) when all that is needed are local range expansions to accommodate its local overlap with Fagaceae etc. These are compatible both with its known ecology and the Cretaceous fossil record of all its four subgenera.
The main massings of the Nothofagus subgenera that you mention are not theoretical, they are simply centres of diversity calculated by counting the extant species: Lophozonia is most diverse in southern South America north of Chiloe I., subgen. Fuscospora in New
Zealand, subgen. Nothofagus in southern South America south of Valdivia, and
subgen. Brassospora in New Guinea and New Caledonia (see my paper in J Biogeogr. 33: 1066. 2006). When the many fossil species of the four subgenera are added in, the locations of the main massings remain the same, suggesting that they have not changed greatly since the subgenera diverged by simple allopatry in the Cretaceous (a minimum, fossil-based age). The local overlap among the four subgenera due to a few outlier species can be attributed to subsequent, local range expansion. As with the family in the order, the subgenera in the genus do not require centres of origin and long distance dispersal by unknown and purely hypothetical means of dispersal that have never been observed. Allopatry followed by local dispersal by normal, observed means explains the pattern.
Wellington, New Zealand.
My papers on biogeography are at: http://tiny.cc/RiUE0
--- On Tue, 27/7/10, Kenneth Kinman <kennethkinman at webtv.net> wrote:
From: Kenneth Kinman <kennethkinman at webtv.net>
Subject: [Taxacom] Nothofagus (Chile-New Zealand distributions)
To: taxacom at mailman.nhm.ku.edu
Received: Tuesday, 27 July, 2010, 1:35 PM
You are correct. I shouldn't have used the word "directly", which
implies a straight line. The Nothofagus driftwood which went from Chile
to Tasmania no doubt was swept north of 30 degrees and then west along
the return current.
However, although this would be true for modern and late Tertiary
ocean currents, some of the dispersals which I am talking about probably
occurred in the early or middle Tertiary when ocean currents in the
southern Pacific were no doubt quite different. Anyway, as far as I am
concerned, the whole Nothofagus biogeography debate is still in the
early stages, and new data could totally change our understanding of how
much vicariance and dispersal each played a role in shaping the present
distribution. The main massings of panbiogeography may well prove to be
overly simplistic in many cases. Only time will tell.
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