[Taxacom] Biogeographical reasoning

[Bob Mesibov]

Karl and Ken,

You're absolutely right that we should only investigate what we can imagine 
today. OK, let's imagine a few possibilities for Nothofagus sp. A (NA), 
which is currently found in New Zealand (NZ):

1. NA has always been in NZ.
1a. NA evolved in NZ within a lineage which has always been in NZ. 
(vicariance)
1b. NA evolved in NZ within a lineage which dispersed to NZ from somewhere 
else. (dispersal)

2. NA dispersed to NZ from somewhere else.
2a. NA evolved somewhere else within a lineage was never in NZ. (dispersal)
2b. NA evolved somewhere else within a lineage which at one time was in NZ, 
but became extinct there. (vicariance/dispersal)
2b. NA evolved in NZ (see possibilities 1a and 1b), became extinct there, 
and re-established in NZ from somewhere else. (vicariance/dispersal)

Note that this enumeration of possibilities assumes that Nothofagus is a 
strictly "cladistic" taxon. If genetic exchange happens in Nothofagus as it 
does in Quercus and Eucalyptus, then NA can have multiple geographical 
ancestries.

It's also assumed above that NZ is a single, isolated landmass. If it's a 
composite landmass and one or more of its components was carrying Nothofagus 
when the terranes docked, then it's not clear to me that 1a and 1b have any 
real meaning.

Sigh. If historical biogeography was a simple empirical science then it 
wouldn't be the godawful mess it is today.
---
Dr Robert Mesibov
Honorary Research Associate, Queen Victoria Museum and Art Gallery
and School of Zoology, University of Tasmania
Home contact: PO Box 101, Penguin, Tasmania, Australia 7316
(03) 64371195; 61 3 64371195

Australian Millipedes Checklist
http://www.qvmag.tas.gov.au/zoology/millipedes/index.html
Tasmanian Multipedes
http://www.qvmag.tas.gov.au/zoology/multipedes/mulintro.html
Spatial data basics for Tasmania
http://www.utas.edu.au/spatial/locations/index.html
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