Re: Avian extinction ref.

[MICHAEL HABIB <habib@jhmi.edu>]

> But until this paper it was not possible to say that it was 
> not man
> _per se_ but the predators he brought with him that caused the
> extinctions.  Not a general homo blitzkrieg, but a specific targeted
> mammal attack!  Not only that, the paper makes the more important 
> claimthat it is the _diversity_ of predators that is critical.

Very true, the importance of predator diversity is quite neat to see.  Just a 
point of caution; I am pretty certain that some human predation  is in fact in 
the dataset.  ie. some of the birds studied were eaten by humans as well.  Not 
that your point doesn't stand, I just wanted to warn you.  Take a look at the 
supplemental material for the paper, I seem to recall that some human predation 
is mentioned in the methods (I'll have to look again myself).

> What I mean is
> inasmuch as these mamals exist on the continents, strategies 
> employed on
> the islands would be disallowed on continents--and species who 
> employedthem became extin
ct when these predatory menageries first 
> appeared.

Ah, yes, well that extrapolation makes sense, assuming you mean 
introduction/migration when you say "first appeared".  If you mean species 
origins, then you have a whole new set of hypotheses to test, because the 
timing is so different (doesn't mean you're wrong, just means you have 
something to work on).  

I am also curious what continental strategies you are thinking may have 
disappeared.  In in particular in mind?  Flightlessness is not nearly so 
prevalent on the mainlands to begin with (the penguins notwithstanding) so I am 
not certain what strategies would "disappear" on the mainland.  Slow life 
histories might be less prevalent.  Ground nesting might be in a few places, 
but overall ground nesters are widespread on both islands and mainlands (IF you 
take into account species relationships.  Ground nesting appears comparatively 
rare on mainlands because of the predominance of arboreal passerines, which do 
not regular
ly reach oceanic islands).

The effect shouldn't be limited to mammals preying on birds, either.  Other 
birds would also be limiting, as would some squamate reptiles.  In fact, I 
think it would be quite interesting if someone looked into similar impacts on 
island faunas with introduced birds.  Predaceous mammal introductions by 
humans, of course, are rather more common.

And again, it is not only a matter of different strategies (such as 
flightlessness).  The confinement of geographic range size is very important.  
Species with small geographic ranges appear to die much more readily than those 
with large geographic ranges.

Definitely a lot of things to think about, and several which presumably relate 
to Mesozoic extinctions.

Cheers,
--Mike Habib