[Taxacom] Tortoise self-rafting sea voyage

[John Grehan]

The statement "trans-oceanic dispersal is assumed to be the mechanism by
which tortoises and many other animals became established on islands
throughout the world" seems to me to be propaganda if the authors fail
to restrict the belief to themselves or a restricted section of the
research community. 

> Try this. "Rafting or drifting between isolated land masses is the
only
> mechanism of dispersal open to many animals." (p2407) They probably
are
> thinking of vertebrates, and note they say animals, not species.

I would call this a rhetorical device as it begs the question of how
does one know this to be the case? In a sense it would seem to be true
of all life - if land masses are "isolated" then by definition the only
mechanisms of dispersal open to animals in one or other land masses are
those that eliminate the isolation.

> The tortoise had a large target - Africa, and one could quibble at the
> trans-oceanic. How narrow does the gap have to be before it's no
longer
> oceanic? But I guess anything off the continental shelf is an oceanic
> traverse.

This is similar to the question of how wide does a 'gap' have to be
before it is considered a barrier, and before one refers to subsequent
isolation as the result of dispersal or vicariance.

John Grehan


> 
> Geoff
> --
>    Geoff Read <g.read at niwa.co.nz>
>     http://www.annelida.net/
>     http://www.niwascience.co.nz/ncabb/
> 
> 
> 
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