New Zealand plants introduced by Chinese?

John Grehan jgrehan at SCIENCEBUFF.ORG
Tue Jul 27 08:40:27 CDT 2004


Ken Kinman wrote:
>      I would agree that invoking "Antarctica hopping" (perhaps
"Antarctica
> bridging" would be a better phrase) is inappropriate for such disjunct
> populations of a single species or even most species groups.
Dispersal by
> mankind, birds, wind, water, or rafting, etc. seems far more likely
given
> the time factor.

I would not presume to say that Ken is necessarily wrong about this, but
what is more 'likely' in biogeography often seems to be more a
reflection of one's personal sense of probability than a necessary
reflection of reality. There certainly seems to be a widespread belief
that a distribution comprising a species level of comparison must
somehow be 'recent'. This seems (I'm using that word a lot here as I may
be mistaken) to be a reflection of the view that if isolated for
sufficient periods of time differentiation should take place to result
in at least different species.

>      However, I do believe Antarctica should be considered as a bridge
(or
> area of origin) for various family group taxa (and even some older
genera)
> with such Nothofagus distributions.  

As I have commented before, there is nothing in biogeographic patterns
to support either view. It seems to be more a theoretical proposition -
either the belief that distributions either side of Antarctica must have
crossed over Antarctica to get to one or other side, or that Antarctica
must be the source. Both propositions seem to be matters of preconceived
Darwinian doctrine than a reflection of empirical evidence.

That includes grass taxa, since
> grasses may be older than we think (Cretaceous would not surprise me)
and
> also that Antarctica may have had habitable areas more recent than
> generally believed.

A agree with both statements here (not that my opinion necessarily
counts for anything). The age of taxa is often presumed on the basis of
the fossil record which is really just a record of minimal dates of
fossilization, or molecular clocks calibrated by the fossil record as an
absolute measure of age. The biogeographic patterns of grasses appear to
be basically the same as life in general and correlated with Mesozoic
tectonics.

I'm not up to date with what is most "generally believed" about the
recency of habitable areas. I would be interested to know what that is
these days. The last I heard was for some surviving Nothofagus on the
trans-Antarctic mountains about 3 myr. 




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