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

[Kenneth Kinman]

 Hi Michael, 
       (1) Well, I have no problem at all with passerines
originating 84 million years ago (and their stem group would be even
older). Their diversity and numbers would have then been severely
reduced (like everything else) during the massive K-T extinction (65
million years ago), perhaps to New Zealand and Australia alone (but a
Paleocene passerine showing up in Antarctica wouldn't exactly shock me;
I always try to anticipate such future surprises).    
      (2) You say the fossil record is probably irrelevant, but I
disagree. Passerines could easily still have been confined to
Australasia by the Early Eocene, but radiated into Eurasia by the
beginning of the Oligocene (probably even later to the New World).
Anyway, it seems safer to me to be a little "ad hoc" (which isn't
necessarily a bad thing) than just brush off the fossil record as
probably irrelevant. 
        (3) The bulk of your post is about mainland
woodpeckers, but I fail to see the relevance since we are talking about
woodpecker taxa trying to disperse to Madagascar, NOT within entire
continents like Africa or Eurasia. Competitive exclusion would be a
major factor in Madagascar, but relatively minor in massive continental
areas. So I would call those arguments largely irrelevant (if not ad
hoc). 
       (4) Likewise, I fail to see much relevance in the
co-occurence of lorises and monkeys in Africa (or Asia), massive areas
compared to Madagascar. Even more importantly, lorises do not dominant
niches in Africa or Eurasia the way that lemurs clearly dominate the
primate niches in Madagascar.  
         (5) And finally, just let me add that even
smaller islands (on both sides of the Wallace Line) would be even more
vulnerable to competitive exclusion. Island jumping across Wallace Line
(in either direction) and then a series of islands would be even more of
a challenge. It would be like running a serial gauntlet. THEREFORE, it
is no wonder marsupials don't occur west of the Wallace Line and certain
vertebrate groups (be they certain primates or rodent taxa or
woodpeckers) failed to traverse that gauntlet in the opposite directon.
And besides competitive exclusion, there is also the problem of
geological volatility (the Toba explosion of the 1880s being just a
recent example) adding to stresses limiting major dispersals of
vertebrates either way along this chain of islands.  The oceanic trench
at the Wallace Line is almost certainly just part of the problem, and
geological factors and competitive exclusion may be bigger factors.  No
wonder marsupials didn't disperse further west, and certain primates,
rodents (as well as woodpeckers) failed to disperse further east.  It's
probably the most treacherous chain of islands in the world (especially
for land vertebrates).  So if those woodpeckers are calling "ad hoc, ad
hoc", who are they actually calling to?  Only time will tell.  :-)
              --------Ken Kinman 
---------------------------------------------- 
Michael wrote:   
        A growing number of ornithologists date the
passerines to the split of the basal New Zealand wrens from the rest and
use the New Zealand/Gondwana rift at 84 Ma (not fossils) to date this
(e.g. Irestedt et al., 2009). The oldest fossil material of passerines
(Eocene, 50 Ma) from Australia and the absence of Eocene passerine
fossils from elsewhere (New Zealand, North America etc.)
are probably not relevant.   
     You explain the presence of passerines, but not woodpeckers, on
Madagascar by suggesting that the southern passerines 'simply got
their first'. But then how did woodpeckers establish an
endemic genus in South Africa (Geocolaptes, sister to - not nested
in! - a widespread African one, Campethera)? Or how did they establish
in South America? Home advantage and competition are important in
explaining why one group doesn't invade the territory of the other, even
though individuals disperse there. But it doesn't explain the origin
of the break in the first place.   The basal genera in woodpeckers are
Jynx: southern Africa to Eurasia and Japan, then Sasia: southern and
central Africa, plus Himalayas to Borneo, then Picumnus: South America
plus Himalayas to Borneo (Fuchs et al., 2006). Did this group really
have a northern center of origin? Even Ernst Mayr (1946), who could
find centers of origin everywhere, admitted that woodpeckers are so
evenly distributed around the world that their center of origin is
impossible to deduce.   
        Your idea that monkeys didn't invade Madagascar because they
were outcompeted by lemurs is ingenious. But monkeys cohabit with
lorises (lemurs' sister-group), throughout their Asian and African
range...  I think I can hear the call of the woodpecker - 'ad hoc! ad
hoc!'