[Taxacom] Biogeographical reasoning

[Ken Kinman]

Bob,
    I believe that the two most likely and parsimonious hypotheses would be 
either 1a (vicariance) or 1b (dispersal).  For instance, N. menziesii has 
probably always been in NZ (and I lean toward 1b being more likely than 1a; 
and I'm pretty sure Knapp et al. would also agree with that).  It could have 
evolved elsewhere (and gone extinct in that region without a trace), but 
that seems even less likely to me.  Anyway, if 1b (dispersal) did occur, the 
one tree of N. cunninghami that reached NZ was the founding ancestor of N. 
menziesii, and thus N. cunninghami is paraphyletic (just like many other 
species that have spun off new daughter species).

    If it was actually vicariance (1a), the most likely scenario would 
probably be a species in New Zealand barely squeaking through the Oligocene 
bottleneck and founding N. menziesii in that manner, although one could 
perhaps argue it was N. menziesii on both sides of the bottleneck since 
species are such "fuzzy" entities in the time dimension.  Luckily, dispersal 
to a new island can make the break much more abrupt (and the line between 
species easier to draw), and I still believe parasitic and/or symbiont taxa 
will help show it was not vicariance in this case.  And hopefully the same 
for the dispersal of Nothofagus gunnii (or cethanica) to found the 
truncata-fusca-solandri group.  It isn't going to be easy or without 
controversy over the interpretations, but it certainly will be interesting.
    -----Cheers,
             Ken Kinman
********************************
Bob wrote:
>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)
>

_________________________________________________________________
>From photos to predictions, The MSN Entertainment Guide to Golden Globes has 
it all. http://tv.msn.com/tv/globes2007/