[Taxacom] Dispersal paradigm (was: Antarctic dispersal)

[Michael Heads]

Hi Richard,

You mentioned vicariance and dispersal in groups other than birds and
plants. Birds are used a lot in biogeography because they're the best known
group, but different groups of algae, fungi, insects, fishes (marine,
freshwater and diadromous), etc. are discussed in my Australasia book as
they illustrate standard patterns.

You suggested that 'there are very, very few generalities we can make
concerning broad patterns in the history of evolution of life on Earth'.
One generality seems to be that the same distributions are, surprisingly,
repeated in groups with completely different ecology and means of
dispersal.

For example, Ken brought up the Madagascar - New Zealand connection in
ratites (elephant birds and kiwis). The same distribution also occurs in
the beetle family Chaetosomatidae, and a correspondent has just written to
me citing a clade of  ducks comprising four NZ species and A. bernieri in
Madagascar (Mitchell et al., 2013). In plants, Euphorbia glauca of NZ is
sister to E.  emirnensis of Madagascar (Riina et al., 2013). These groups
all have very different ecology and means of dispersal, suggesting that
these factors are not the cause of the pattern.




On Wed, Jun 18, 2014 at 12:02 PM, Richard Pyle <deepreef at bishopmuseum.org>
wrote:

> Just a quick addition to Jason's comments (I've been loosely following
> this thread, and generally find myself nodding in agreement with Jason):
>
> > Firstly, that geological dates are a range,
> > from first opening to last connection (and I am ignoring the uncertainty
> in
> > determining each of those dates, so there are ranges to each of your
> > endpoints). Secondly, that taxa will vary in their response to the
> barrier
> > emerging. Some will be cut off immediately, others will be able to cross
> it for
> > a while, while others may have populations right around the barrier. With
> > such complex scenarios the idea that you can collapse multiple splitting
> dates
> > into a single common one is just not possible. The current iterative
> method,
> > albeit imperfect, serves better the purpose of crosschecking (our
> differing
> > opinions on dispersal not withstanding).
>
> It's also important to remember that speciation also happens across a
> range of time.  Even in cases where populations were instantaneously split,
> the sub-populations on either side of the barrier don't themselves
> instantly become distinct species. Time has to pass, populations diverge,
> biological barriers to reproduction happen.  The scale of time represented
> by this range of speciation time no-doubt varies according to the biology
> of the particular organism, and the magnitude of selection pressure or
> drift or environmental mutagens or whatever -- but I imagine that it may
> well overlap with the scale of time across which vicariant events occur.
>
> Which brings me back to the question I asked some months ago.... What,
> exactly are we debating?  Has someone claimed that vicariance plays
> absolutely no role in the history of speciation?  Has someone claimed that
> dispersal plays absolutely no role in the history of speciation?  Has
> someone claimed that allopatry is always a necessary component of
> speciation (and what definition of "allopatry")?  Are we really just
> arguing about what has played the *most important* role in the overall
> history of evolution on this planet?  If so, then do we really make any
> progress in addressing  that question by extolling on this particular bird
> or that particular plant?  What about fishes? (Freshwater? Marine?)  What
> about insects?  What about fungi?  What about algae? What about plankton?
> What about bacteria?
>
> Perhaps the only generality one can make concerning broad patterns in the
> history of evolution of life on Earth is that there are very, very few
> generalities we can make concerning broad patterns in the history of
> evolution of life on Earth.
>
> Aloha,
> Rich
>
>
> Richard L. Pyle, PhD
> Database Coordinator for Natural Sciences
> Associate Zoologist in Ichthyology
> Dive Safety Officer
> Department of Natural Sciences, Bishop Museum
> 1525 Bernice St., Honolulu, HI 96817
> Ph: (808)848-4115, Fax: (808)847-8252
> email: deepreef at bishopmuseum.org
> http://hbs.bishopmuseum.org/staff/pylerichard.html
>
>
>
>
>
>
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-- 
Dunedin, New Zealand.

My recent books:

*Molecular panbiogeography of the tropics.* 2012. University of California
Press, Berkeley. www.ucpress.edu/book.php?isbn=9780520271968

*Biogeography of Australasia:  A molecular analysis*. 2014. Cambridge
University Press, Cambridge. www.cambridge.org/9781107041028