[Taxacom] Seed plants of Fiji

[Karl Magnacca]

On Thu, November 16, 2006 1:43 pm, John Grehan wrote:
> How do you know the 'barrier' is pertinent to the distribution in the
> first place, or that it is a 'barrier'?

In many cases of hypothesized vicariance, the barrier is hypothetical.  In
this case, it's because you're talking about terrestrial organisms that
cannot survive in the sea crossing 1000+ miles of ocean and landing on a
tiny speck of land.

> The biogeographic evidence is that the Hawaiian islands support biota
> that comprise vicariously distributed groups in the Pacific and standard
> tracks across the Pacific. There are innumerable examples in the
> literature, but take a look at the Meterosideros example as a starter,
> and Springer's book on Pacific shorefishes, Heads articles on Coprosma,
> etc.

What makes you think Metrosideros is vicariant rather than dispersed?  It
produces millions of tiny wind-dispersed seeds, so absent other evidence
trans-oceanic dispersal seems much more likely.

>> I think there are two problems with this discussion.  First is that
>> you seem to be using a different definition of "vicariance" than
>> everyone else.
>
> Everyone?

Well okay, everyone I've heard use the word.

> I am referring to vicariant form-making.

Meaning what?

> All of this is nice theory,

I'm just talking about the definition of the word "vicariance", it has
nothing to do with theory.

> Mobilism within vicariant ranges maintains the existence of the taxon
> without obliterating the underlying vicariism.

Mobilism on that scale across hundreds of miles of ocean = not bloody likely.

> No - just did not leave behind a stratigraphic trace as the current site
> of the islands, just as there is no trace left at the Galapagos even
> though many geologists accept the possibility of a former island arc
> connection.

It looks to me like there is a ridge that extends from the Galapagos to
South America.  If you're saying there's just no trace at the "current
site of the islands", you need to explain a) how the islands got to where
they are, and b) how the seafloor around them got smoothed out.

> They neither help nor hinder if one accepts that biogeography
> constitutes an independent research program with its own methods and
> principles. That is true of panbiogeography, but it may not be true of
> all other methods. There are geologists who have suggested such
> structures as I have talked about, but you wont see them by just looking
> at a map of the Pacific.

But when you have a system that produces conclusions that another area of
science says is impossible, you need to sit down and figure out which one
of them is wrong.  Otherwise, as Mike said, you just have religion. 
Nothing you've said has actually challenged standard geology, just that
your conclusions say the geology is wrong, therefore it must be.

Karl
=====================
Karl Magnacca, UC-Berkeley
ESPM Dept., 137 Mulford Hall #3114
510-642-4148