[Taxacom] metapopulations (excerpt from ongoing discussion)

[John Grehan]

Not quite sure of what you are getting at Stephen, but before India
collided with southern Asia there may have already been an 'Andean' type of
orogeny present, and India was not the only geological unit to collide as I
understand that it was preceded by one or more island arcs. Anyway, once
collection took place some organisms appear to have expanded their range to
include parts of Asia and vice versa, and some did not expand (as in some
Indian taxa that have their nearest relatives in Madagascar or Africa).

Cheers, John

On Thu, Sep 23, 2021 at 5:15 PM Stephen Thorpe <stephen_thorpe at yahoo.co.nz>
wrote:

> So, perhaps an interesting case in biogeography is the sort of "reverse
> vicariance" presumably involved when the Indian subcontinent joined Asia?
> Though pushing the Himalayas up may have created a dispersal barrier?
>
> On Friday, 24 September 2021, 03:59:37 am NZST, John Grehan via Taxacom <
> taxacom at mailman.nhm.ku.edu> wrote:
>
>
> I separted this out of the ongoing thread for ease of reference.
>
>
> > " Surely vicariance is such that the distance between landmasses varies
>
> > over time and the chances of dispersal between the landmasses decreases
> as
>
> > the distance between them increases. In practice, vicariance itself may
>
> > involve dispersal over short distances. As the distance increases, the
>
> > fewer species are able to disperse.Stephen"
>
> >
>
>
> Yes. It's a simple exponential decay with each taxon having a different
>
> ability to disperse and an element of serendipity thrown in. Beyond the
>
> phylogenies and the macrobiogeographical patterns there have been plenty of
>
> experimental studies looking at island colonization (Simberloff & Wilson
>
> for example) that show this pattern. It is like arguing that microevolution
>
> experiments/observations don't support evolution. Anyway, back to the cage.
>
>
> Jason
>
>
> Jason & Stephen – you are both right in my view - that vicariance does
> involve dispersal, but not just over short distances, since some ancestral
> ranges were nearly global. The experimental studies of island colonization
> are part of the picture as they illustrate the process of species survival
> and persistence. The islands studied by Simberloff & Wilson are
> biogeographically no different from disjunct habitats within a continent. A
> species may occupy multiple islands or habitats, and yet also be allopatric
> with respect to sister taxa, and the allopatry may involve a tectonic
> correlation. This is perhaps the key fact (it's indisputable since tectonic
> correlations are observable) of biogeography (and evolutionary ecology to
> boot). Heads synthesized these facts under the metapopulation concept –
> that because organisms disperse (in the ecological sense of ordinary means
> of dispersal that are empirical and therefore observable) they are able to
> maintain their existence over long periods of time, even though individual
> habitats/islands may be ephemeral. This is well illustrated by the
> Galapagos where organisms that are able to disperse between islands over
> geological time have been able to persist at the hotspot since Mesozoic
> time. Gary Nelson pointed out a long time ago that their experiment can be
> replicated in one's backyard garden by sterilizing an area of soil and
> watching plants 'colonise' the exposed surface. Wonderful how one can do
> studies relevant to evolutionary biogeography in one's own backyard (if one
> has a backyard of course).
>
> The bottom line in all of this is that tectonic correlations have been
> documented for hundreds of taxa. This is the great lacuna in the science of
> biogeography (i.e. usually treated as if it does not exist). It has to be
> addressed as a reality (however 'explained'), not simply ignored (which is
> most often the case). Tectonic correlation is consistent with vicariance
> and ecological dispersal, not 'random', 'chance' or 'freak' dispersal that
> is supposed to have almost always occurred only once in a taxon, and yet
> the same tectonic correlations for taxon after taxon. Tectonic correlation
> shows that biogeography should, at least alongside modern genetics, be at
> the core of any evolutionary program and synthesis, not just an obscure
> hobby for some.
>
> Cheers, John Grehan
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