[Taxacom] Dispersal paradigm (was: Antarctic dispersal)

[Richard Pyle]

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
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