[Taxacom] Woodpeckers: If any got to Madagascar, they were probably too late

[Michael Heads]

Hi Ken,
 
Your argument hinges on a northern center of origin of woodpeckers and a southern center for passerines. But this is based entirely on the idea that a basal clade in a group (e.g. New Zealand wrens in passerines) represents a center of origin for the whole group. Why can't it be a center of differentiation in a group that was already cosmopolitan? Anyway, woodpeckers are accepted as good dispersers, e.g. they are on Jamaica, which as everyone knows was completely submerged by the sea and the entire biota derived by trans-oceanic dispersal from the mainland. There are also endemic genera on Cuba and Hispaniola. But woodpeckers never crossed the 20 km Salue Timpaus Strait to get from Sulawesi to anywhere in Australasia. Why not? Could it be something to do with this being the same strait that monkeys stop at, although when introduced to New Guinea they  become weeds (macaques)? Both monkeys and woodpeckers are also absent from Madagascar.
 This global pattern occurs in the two groups, also sciuromorph rodents, and many others with completely different ecology, behavior, means of dispersal etc., so I don't think these factors can be important in explaining the pattern.      
 
Michael 

Wellington, New Zealand.

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

--- On Thu, 19/5/11, Kenneth Kinman <kennethkinman at webtv.net> wrote:


From: Kenneth Kinman <kennethkinman at webtv.net>
Subject: [Taxacom] Woodpeckers: If any got to Madagascar, they were probably too late
To: taxacom at mailman.nhm.ku.edu
Received: Thursday, 19 May, 2011, 2:28 PM


Hi All,
      I was thinking about the failure of woodpeckers to become
established in Madagascar (or more importantly in Australasia).  Again,
I have to assume competitive exclusion as the major factor.   
      Firstly, woodpeckers are certainly not the most migratory groups
of birds.  Compared to song birds in general and various other groups
which are more migratory, they aren't likely candidates to be early
dispersers to isolated habitats.  Most woodpeckers tend to stay in a
relatively limited range year-round.      
     Furthermore, they are thought to have originated in the northern
hemisphere, while Passeriformes are thought to have originated in the
southern hemisphere.  Passeriforms thus had the home court advantage in
the south (even ignoring the fact that they are, as a group, better
migrators). 
       Therefore, once the northern woodpeckers finally reached Africa,
they probably had a fighting chance in some niches continent-wide.
However, even if such relative-non-migrators reached Madagascar at all
(admitedly a possibility given millions of years), a well-entrenched
fauna of passeriforms, cuckoos, rollers, and other birds would have made
life miserable, if not impossible, for such johnny-come-latelies in
Madagascar.  In the Americas, woodpeckers seem to have had better luck
diversifying in the extremely diverse environments in  South America (at
least compared to out lying areas in the Old World like Madagascar or
Australasia).   
      As for Australasia, passeriforms were clearly there by the early
Eocene of Australia, and presumably earlier.  If woodpeckers had even
tried to disperse over the Wallace Line (doubtful for a group not adept
at migration or rapid expansion), a well-entrenched and diverse
passeriform population would have most likely eliminated the invaders by
competitive exclusion at various steps of attempted island-hopping.  And
that is not even considering other competitors from other Orders of
birds, or even pressures from birds of prey or non-bird predators which
such northern birds would have not evolved much ability to confront.
Given all of that, I feel little need to worry too much about molecular
clocks or even sparse fossil records.  Woodpeckers probably had little
chance invading (becoming established in) either Madagascar or even the
outskirts of Australasia. 
              -------------Ken


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