[Taxacom] Madagascar (was: Timeline of Life)

[Kenneth Kinman]

Hi Michael, 
       Perhaps the main reasons would be: Failure to
Establish. Over millions of years, there are no doubt many dispersals
that simply fail. If it only involves a single male or a single
non-pregnant female, the dispersal obviously fails to establish a
population. And even if initially successful, inbreeding can result in a
small population eventually going belly up (even under circumstances
that are otherwise favorable).                 
       This would be especially true for those mammals
which have very few young at a time. On the other hand, a fertilized
crocodile producing a large batch of young after reaching another
continent would have a better chance of beating the odds (and inbreeding
tends to be less detrimental to reptiles than to mammals). And having
precocial young would also be helpful in establishing a population and
reducing generation time.    
       But getting back to Madagascar, once lemurs were well
established, it would have been much harder for any other primates to
attempt to establish a population there, because they would face
competition in addition to all other difficulties.  Unless a second
invader is lucky or can find an unoccupied niche, it is unlikely to
become established.      
          ----------Ken                          
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Michael wrote:  
            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.