[Taxacom] Panbiogeography

[Michael Heads]

Hi Jason,

Thanks for all the useful references. You cite Rossberg et al. 2013 on
meiobiota, which suggests that ecospecies might only occur in organisms
with body sizes exceeding the millimetre scale. As you imply, this would
mean that there could not be a biogeography of microorganisms, at least in
the meiobiota. But there are there are many empirical studies that
demonstrate well-defined genetic species in meiobiotal organisms (Morgan et
al., 2014 Proc Roy Soc B). Google scholar shows 412 papers
citing 'everything is everywhere' since 2012 (nearly all on
microorganisms), so it does seem to be an important discussion, with
obvious implications for phylogeny, biogeography, ecology, medicine,
conservation etc.

Sympatric speciation: I don't think I explained my example very clearly, so
here's another attempt. Consider a large area of rainforest, hundreds of km
across. Within it, there are several allopatric species with ranges of say
20 km across, all found throughout their respective areas, both on the
ridges and in the gullies. This sort of thing is very common. In one of
these species, ecological differentiation (with no geographical component)
divides the species into a ridge species and a gully species. (Again, this
is one of the main environmental heterogeneities in many areas, and sorts
many non-sister species). You pointed out that the new ridge species might
migrate to other ridges outside its ancestral area - but there are *already
*species present on the ridges in the other areas.

The pattern I've just described, in which sister species are ecologically
differentiated but have the same geographic distribution, is what you would
expect with sympatric speciation, but it doesn't seem to occur (ever?). Of
course countless groups *do *show ecological differentiation but the same
distribution (this is the basis of panbiogeogrphy), but they are not sister
species.

The Bolnick and Fitzpatrick (2007) review in Ann. Rev. Ecol. Syst. cites
the example of the two sister species of palms on Lord Howe Island as 'a
leading case' (i.e. cited lots), but the original account (Savolainen et al
Nature 2006) is very naive geologically and there are no distribution maps.
They just say that both species 'occur sympatrically in 11 out of the 55
quadrats that contain palms', which suggests a high level of allopatry. The
island is a tiny, eroded remnant of a former, larger structure on a
seamount chain and, not surprisingly, organisms endemic there have been
dated as older than the island itself. The example is discussed in more
detail in my 2014 book.

The Peccoud et al. paper (PNAS 2009) supporting sympatric speciation in pea
aphids of France and Germany also doesn't give maps - it just lists the
species distributions in terms of three areas: 'eastern France',
'northwestern France' and 'eastern Germany'. If two forms overlap in one of
these areas, the authors regarded them as sympatric! It's like saying three
species are endemic to Australia, and so they are sympatric. This is
exactly the same point that Pierre Deleporte made a few days ago - there is
no excuse in the 21st century for not presenting distribution maps or
listing areas at the appropriate scale.

Michael




On Thu, Apr 24, 2014 at 4:53 PM, JF Mate <aphodiinaemate at gmail.com> wrote:

> Michael,
>
> got the article you mentioned and it is a nice read. I still wouldn?t call
> it a paradigm shift or keep repeating Beijerinck?s motto. It is
> particularly telling that the author doesn?t refer to any particular paper
> from the 1920?s-1960?s regarding prokaryote biogeography, probably because
> nobody was looking anyway.
>
> As to the deeply structured nature of microfaunal populations, you should
> read Rossberg et al 2013 (Are there species smaller than 1 mm? Proceedings:
> Biological Sciences, Vol. 280(1767):1-7).
>
> Finally, in regards to the example you mentioned, you will find a selection
> here (seeDOI: 10.1146/annurev.ecolsys.38.091206.095804). Mostly fish, so
> way out of my depth. There is also a more recent paper on the pea aphid
> which probably comes closest to documenting the range between structured
> populations to incipient species in a sympatric scenario (Peccoud et al,
> 2009). I was going to mention head/body lice but currently (to my surprise)
> it is not clear if they are subspecies or just ecotypes and what the
> mechanism is that accounts for the phenotypic differences. Who knew.
>
> 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