[Taxacom] an interesting paper on Long Distance Dispersal

Michael Heads m.j.heads at gmail.com
Sat Jul 7 21:10:44 CDT 2018


Hi Les,

Your post raises some interesting points.

What is the significance of the movement of individuals for biogeography?
Do such movements create the distributions of clades or cause speciation?

Dispersal theory proposes that ‘When lineages arrive in new habitats they
will usually diverge and sometimes speciate’ (Renner 2005, p. 550).
However, this process differs from the dispersal observed every day; any
patch of cleared garden will soon be colonised by the local weedy or
pioneer flora and fauna, and later by less weedy taxa, but none of these
will diverge or speciate there. This colonisation is ‘normal’ or
‘ecological’ dispersal. The distinction can be made between biogeographic
dispersal (a mode of speciation) and normal, ecological dispersal (without
speciation).

Some authors (including Jason in an earlier post) suggested that the
distinction is merely semantic. However, it is now being adopted in
completely orthodox textbooks. For example, Lomolino *et al*. (2010, p.
170) wrote that ‘The role of dispersal in biogeography is thus very
different from its role as a demographic phenomenon’.

The theory of founder dispersal does not really explain why movement
between populations would be occurring at one time, but then, at some
point, stop or at least decrease, allowing differentiation to proceed. What
is the reason for the change? In dispersal theory, the factor is ‘chance’.
In panbiogeography, it is tectonic or climatic change.


Lomolino MV, Riddle BR, Whittaker RJ, Brown JH (2010) ‘Biogeography’. 4th
ed. Sinauer Associates, Sunderland.

On Thu, Jul 5, 2018 at 5:41 AM, Les Watling <watling at hawaii.edu> wrote:

> Apropos the recent discussion re dispersal vs vicariance. As a recent paper
> in PeerJ makes clear, the size of the dispersing organism matters. As does
> mobility, and a host of other factors.
>
> In the case of tardigrades it was long assumed that wind was the major
> dispersion agent, but the authors demonstrate, as much as one likely can,
> that bird feathers are an effective agent for something as small as a
> tardigrade.
>
> https://peerj.com/articles/5035/
>
> Not a too-likely method for primates other than in sci-fi stories(!).
> Primates probably could wander long distances, but why would they?
> Especially if their needs are being met where they are. In which case
> rafting on continental chunks might be what carries them around.
>
> But I think bird feathers also work for seeds of some species, and
> something as unusual as terrestrial amphipods. In Hawaii, some animals,
> such as terrestrial amphipods have no likelihood of dispersing over the sea
> on rafts or other floating objects because of their osmotic intolerance to
> sea water. On the other hand, we also know that certain marine taxa, such
> as cumaceans, which are small benthic crustaceans with almost no swimming
> ability and no larvae, have not made it to Hawaii. Most likely that is
> because they could only get there by travelling along the bottom, meaning
> they would have to crawl through the abyss.... not going to happen,
> temperature and pressure. But 3 species of cumaceans have now made it, most
> likely in ship ballast water.
>
> As with cumaceans, shallow water octocorals, a regular feature of most
> tropical coral reefs, are essentially absent from Hawaii. There are a few
> (maybe 4?) species of very small soft corals that can be found in shallow
> pools or in water a few meters deep. But the normal reef habitat has no
> octocorals. However, at depths greater than about 350 m, octocorals become
> abundant and diverse, exceeding more than 100 species, and inhabiting
> depths to over 3000 m. So the deep sea species have made it, easily, but
> the shallow species have not. Low dispersal capability in the latter, and
> long distance larvae in the former?
>
> In the end, I think the debate needs to be more carefully circumscribed
> with respect to the organisms. And, from where I sit, I see both
> panbiogeography and LDD each explaining some patterns.
>
> Best,
> Les
>
>
>
>
>
>
> Les Watling
> Professor, Dept. of Biology
> 216 Edmondson Hall
> University of Hawaii at Manoa
> Honolulu, HI 96822
> Ph. 808-956-8621
> Cell: 808-772-9563
> e-mail: watling at hawaii.edu
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-- 
Dunedin, New Zealand.

My books:

*Biogeography and evolution in New Zealand. *Taylor and Francis/CRC, Boca
Raton FL. 2017.
https://www.routledge.com/Biogeography-and-Evolution-in-New-Zealand/Heads/p/book/9781498751872


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


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


*Panbiogeography: Tracking the history of life*. Oxford University Press,
New York. 1999. (With R. Craw and J. Grehan).
http://books.google.co.nz/books?id=Bm0_QQ3Z6GUC
<http://books.google.co.nz/books?id=Bm0_QQ3Z6GUC&dq=panbiogeography&source=gbs_navlinks_s>


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