[Taxacom] Madagascar (was: Timetree of Life)

[Robin Leech]

Michael,
My Accam's Razor answer is that they haven't gotten there yet.
Robin

----- Original Message ----- 
From: "Michael Heads" <michael.heads at yahoo.com>
To: <taxacom at mailman.nhm.ku.edu>
Sent: Wednesday, May 18, 2011 2:23 PM
Subject: Re: [Taxacom] Madagascar (was: Timetree of Life)


Hi Ken,

Yes, but WHY exactly is it so difficult and rare for highly mobile animals 
such as primates, rodents, woodpeckers etc. to disperse to Madagascar? These 
groups have only one, one and no clades there, respectively. Very strange. 
Likewise, why have non-human primates never invaded Australasia? You suggest 
competitive exclusion for the absence of the rodent clades there but an 
introduced primate species (a macaque) is a 'weed' in west New Guinea. It 
seems that competition may explain why the pattern is preserved, but not how 
it originated in the first place.

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] Madagascar (was: Timetree of Life)
To: taxacom at mailman.nhm.ku.edu
Received: Thursday, 19 May, 2011, 4:20 AM


Hi Michael,
Well, the lack of Hystricomorpha, Sciuromorpha, and various other
taxa in Madagascar would be most parsimoniously explained by the
difficulty and rarity of dispersal from mainland Africa to Madagascar.
It is probably largely by chance that lemur ancestors floated
over on trees. However, such dispersal is not so unlikely that I would
turn to a vicariance explanation for lemur origins. It seems extremely
unlikely to me that lorises and lemurs split before the K-T extinction.
----------Ken
P.S. The lack of certain rodent taxa in Australasia may be due to a
more complex combination of factors, but competitive exclusion is one
likely factor in such taxa attempting to island-hop into that area
(perhaps more so than the isolation afforded by the Wallace Line).
---------------------------------------------------------
Michael Heads wrote:
The trans-Atlantic pattern can be approached in the broader context
of the main rodent clades. It has to be explained together with
the fact that Hystricomorpha are not in Madagascar and are east
only to Borneo (cf. strepsirhines), while Sciuromorpha (squirrels) are
not in Madagascar and east only to Sulawesi (cf. haplorhines). Many
authors have commented on the absence of these groups from both
Madagascar and Australasia (cf. woodpeckers etc.). An
overall dispersal account for the rodents doesn't really explain
these interesting eastern limits in two of the three main rodent
groups, or their repetition in the primates and others.



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