[Taxacom] Panbiogeography

[JF Mate]

Yes Stephen, I agree, but I am trying to keep it simple and look where
it got me!

Best

Jason

On 28 March 2014 21:51, Stephen Thorpe <stephen_thorpe at yahoo.co.nz> wrote:
> Dispersal can also occur passively, by rafting on floating chunks of
> habitat, or phoresy on other animals
> From: JF Mate <aphodiinaemate at gmail.com>
> To: Taxacom <taxacom at mailman.nhm.ku.edu>
> Sent: Saturday, 29 March 2014 9:43 AM
> Subject: Re: [Taxacom] Panbiogeography
>
> Dear John
>
> after looking at you replies I have realised that we are chasing each
> other in circles and that you constantly refer to Michael´s book when
> I seek a more concrete answer. This makes it rather difficult and
> unproductive. So, I will simply state the following definitions under
> which I operate:
>
>
> -Dispersal: change in location. The difference between long range and
> short range is merely in the probability of each resulting in
> successful (i.e. surviving and reproducing). "Short" and "long" are
> taxon and site specific.
>
> -Barrier: impediment to movement. When I defined what a barrier was I
> failed to consider partial blockage but instead opted for a binary
> barrier. I see this was a mistake on my part, so I hope this will
> clear the matter.
>
>
> Dispersal by insects >100Km from the source (mostly coastline) are
> very common, even when flying a few meters above the surface.
> Transoceanic flights by large, easily noticed insects (mostly
> butterflies) have been documented several times in recent times.
> Considering that there are observed examples of organisms dispersing
> beyond barriers (usually crossing bodies of water) I think dispersal
> is a valid mechanism.
>
> Furthermore the lack of genetic structure in many insect species, even
> in discontinuous ranges spanning thousands of kilometers indicates a
> fair degree of dispersal. Granted that the opposite is true and
> particularly striking examples are common (headwater stream insects
> for example). But since examples from both mechanisms can be found, I
> don´t feel this somehow disproves the other.
>
> As to your statements, I feel a couple are inconsistent. I would be
> grateful for a clearer explanation:
>
> "... but when there is a biogeographic break correlated with a
> tectonic break there is reason to consider that they are related. ...
> The panbiogeographic method is about pattern analysis. In principle,
> distribution data provide an empirical resource. Speculations about
> imagined chance dispersal does not."
> So what happens when a biogeographic break and a tectonic one do not
> coincide? Furthermore, correlation is not necessarily causation, so
> don't panbiogeographers also speculate?
>
> "No, the patterns make the theory problematic as the patterns are
> incongruous with the expectations of chance dispersal. ... However you
> chose your words, the point is that panbiogeographic analysis shows
> that distance is not a predictor of distribution range for
> differentiated taxa so the 'probabilities' are contingent upon the
> relevant factors of geological, climatic, or human disruption.'
> If dispersal is random, the result of the interaction of numerous
> factors, is it suprising that simply using one (distance) doesn't
> work? An island may be upwind and therefore rarely receive flying
> insects from the minland whereas a more distant, downwind island can
> receive a fairly constant rain of wind-carried organisms. Gillespie et
> al provide a nice review.
>
> "When it comes down to explaining vicariant patterns the principal
> choice has been to frame the origin in terms of dispersal from centers
> of origin."
> I feel otherwise.Can you please support this argument?
>
> Best
>
>
> Jason
>
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