[Taxacom] Panbiogeography

[Michael Heads]

 Hi taxacomers,

Jason Ali just sent me a copy of his latest paper with Jonathan Aitchison,
on the Galapagos (J. Biogeog., hot off the press). It explains the geology
over the last 700 000 years and uses this to explain distributions in some
of the plants and animals - but not the mocking birds! Here's my reply:



Thanks for the useful paper. The classic group for biogeography on the
Galapagos are the mockingbirds, Nesomimus (now a clade in Mimus), that
Darwin (1859) gave as the 'type' example of allopatric species (the more
famous 'finches' are not allopatric, although many people assume they are!):



'In the Galapagos Archipelago, many even of the birds, though so well
adapted for flying from island to island, are distinct on each; thus there
are three closely-allied species of mocking-thrush, each confined to its
own island...'. [7 distinct forms are now recognised].



Arbogast et al. (2006) showed that the sister group of the Galapagos clade
is M. gundlachii of Jamaica/Bahamas, the standard Galapagos - Caribbean
connection. Within the Galapagos, the clade on the outer eastern 'arc':
Espanola/Genovesa/San Cristobal is sister to (and allopatric with) the
other Galapagos clade.



Michael


On Sun, Apr 20, 2014 at 1:56 PM, Michael Heads <m.j.heads at gmail.com> wrote:

> Hi Jason,
>
> You should be able to find a free version of the O'Malley paper using
> 'google scholar' ('apps' button on google). A similar paradigm shift to
> that seen in microbiology has also happened in marine biology - huge
> amounts of allopatric structure, even down to small scales,  have been
> discovered in what were thought to be widespread taxa dispersed by
> currents. I wrote a review in 2005, 'towards a panbiogeography of the
> seas', which is also freely available at google scholar.
>
> Here's another example of what I'm talking about with sympatric
> speciation. Imagine a species of liverwort found in an area of hill forest
> 50 km across, that diverges by ecological, sympatric speciation into one
> species found on the tops of leaves, and its sister on the underside. This
> process would give groups with different ecology but very similar
> geographic ranges.  (Of course, one or both species may subsequently expand
> or contract their geographic range).  Such a pattern would be
> solid evidence for sympatric speciation, but most studies claiming
> sympatric speciation don't provide anything like this. If there is the
> slightest overlap between two sister species, many studies now claim
> sympatric speciation. The process may occur, but it seems to be very rare.
>
> Michael
>
>
> On Sun, Apr 20, 2014 at 11:48 AM, JF Mate <aphodiinaemate at gmail.com>wrote:
>
>> Dear Michael:
>>
>> "Another colleague sent a good paper on the 'everything is everywhere'
>> debate - it's:
>> O'Malley, M. A. (2007). The nineteenth century roots of'everything is
>> everywhere'. Nature Reviews Microbiology, 5(8), 647-651. 'The
>> identification of geographical patterns in microbial distributions has
>> begun to challenge purely ecological explanations of biogeography and
>> the underlying principle of 'everything is everywhere: but the
>> environment selects'.' It's a good review."
>>
>> I don?t have access to this paper so I cannot add anything to this.
>> Nevertheless, what are you using to substantiate your next comment?:
>>  "Of course, no-one is suggesting that dispersal does not occur, but
>> chance dispersal/ecology does not seem to be the explanation for these
>> patterns."
>> What is chance ecology? Which patterns do you refer to? Pantaneto and
>> colleagues are careful to note that, although certain lineages in
>> their phyla show the effects of vicariance, a large proportion of
>> their taxa are indeed widely dispersed (they use the term themselves).
>> So how does this negate dispersal? Again, nobody denies vicariance, or
>> that it may be more important than dispersal in many situations or at
>> particular scales, but the evidence of dispersal is rife so unless
>> there is a testable hypothesis to distinguish your two dispersals, we
>> will be arguing forever and not make any progress,
>>
>> As for sympatric speciation and range overlap, range overlap of the
>> hosts/habitats may or may not be fully concordant. So why would your
>> ridge species simply stay on that ridge? Why would adaptation to a
>> ridge not preadapt it to living on cliffs? We call it a ridge but for
>> your species it may be an inaccessible area due to dryness, exposure,
>> temperature oscillations, etc. Once the problem is solved, there are
>> other ridges to move into or other "ridge-like" environments that are
>> suddenly accessible. Once a new niche is broken into the range
>> limitations of the ancestral population/species will no longer fully
>> apply. In addition, consider that, it is likely that most of these
>> jumps will occur at the edges of a range, where a species? survival
>> chances are at their limit (high selective pressures); where gene-flow
>> may also be limited (distance to bulk of population gene-pool,
>> suitable habitat is more fragmented hindering migration); and where
>> the population may be small (drift more likely) the resulting
>> ditribution will show little overlap.
>>
>> Best
>>
>> Jason
>>
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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—80520271968
>
> *Biogeography of Australasia:  A molecular analysis*. 2014. Cambridge
> University Press, Cambridge. www.cambridge.org/9781107041028
>



-- 
Dunedin, New Zealand.

My recent books:

*Molecular panbiogeography of the tropics.* 2012. University of California
Press, Berkeley. www.ucpress.edu/book.php?isbn—80520271968

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