[Taxacom] Fwd: Woodpeckers, primates, as well as the Wallace Line gauntlet

Michael Heads michael.heads at yahoo.com
Sat May 28 16:46:26 CDT 2011


Hi Jason,
 
Ecological or 'normal' dispersal, e.g. a weed arriving in a garden, is the simple movement observed every day and does not involve speciation. 'Chance dispersal' is a mode of evolution proposed to explain, for example, platyrrhines in America or lemurs in Madagascar. 
 
You suggest that some truly horrendous dispersers 'have indeed made it'. Do you have any examples? Are you suggesting coco de mer is on the Seychelles because of chance dispersal? 
 
You say: 'although you could hypothesize that terrestrial biota in Pacific islands will probably originate from nearby islands...  you will never be able to say of each taxon that it has indeed originated in this way unless you gather your data (phylogeny, distribution, fossils or remains, etc) and analyze it'. I agree completely! 
 
You write that: 'If the closest groups to your ingroup happen to come from a mainland source or from a distant source then you can´t say much other than what the data suggests'. Of course, but what exactly do the data suggest? For example, seamounts in the Musicians group (NE of Hawaii) were recently discovered to have flat tops,  i.e. they were formerly above sea-level and have been planed flat to sea-level by wave erosion before eventually subsiding below sea-level. At one stage they would have maintained a terrestrial biota.
 
Finally, you write: 'You could argue for disappeared islands as the sources or stepping stones but this is an ad hoc argument and much more complicated than allowing for chance'. It's not ad hoc because there is excellent geological evidence for former islands. 
 
Michael

Wellington, New Zealand.

My papers on biogeography are at: http://tiny.cc/RiUE0

--- On Sun, 29/5/11, Jason Mate <jfmate at hotmail.com> wrote:


From: Jason Mate <jfmate at hotmail.com>
Subject: Re: [Taxacom] Fwd: Woodpeckers, primates, as well as the Wallace Line gauntlet
To: "Taxacom" <taxacom at mailman.nhm.ku.edu>
Received: Sunday, 29 May, 2011, 4:14 AM



Dear Michael,

my reply was aimed, specifically, at these sentences in you previous post:

Using chance (dispersal) to explain a pattern is just nihilism and leads
> > nowhere.

I
> > can't see the concept of chance dispersal lasting much longer. Once it's
> > dropped, a real science of biogeography may develop. 

Chance dispersal and ecological dispersal are not as different as you may think. If an island is in the Pacific it is logical to suppose that the sources of possible immigrants will be from nearby pacific islands/biotas and also from taxa that, from one reason or another, are better adapted to island life or preadapted (by chance) to their next port of call. But it is still chance. Many are called but only a few are chosen. Why? Some taxa are indeed brilliant at dispersing (coconuts) whereas others aren´t (Coco d´mer) but some truly horrendous dispersers have indeed made it. Thus although you could hypothesize that terrestrial biota in Pacific islands will probably originate from nearby islands and mostly by taxa that are good colonizers (I guess it is this explanatory power that you think is important), you will never be able to say of each taxon that it has indeed originated in this way unless you gather your data (phylogeny, distribution, fossils or
 remains, etc) and analyze it. If the closest groups to your ingroup happen to come from a mainland source or from a distant source then you can´t say much other than what the data suggests. You could argue for disappeared islands as the sources or stepping stones but this is an ad hoc argument and much more complicated than allowing for chance. Also keep in mind that ad hoc explanations can play both ways.

Best

Jason

                          
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