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Re: Avian extinction ref.
> In fact, I think T.E.
> Martinhas done a study comparing N hemisphere vs. S. hemisphere
> birds. S. H.
> birds are less preyed upon and have the above luxuries.
Sounds like a neat study, do you have a full ref by any chance?
> OK...but on mainlands there are many more restrictions on species that
> ground-nest. I have argued here before that size is a limit on
> continentsbecause it allows discovery...and so this body plan is
> only workable in
> few mainland biomes--e.g., areas of low predator density
> ("islands" of low
> predator density) such as the ostrich in the arid savanna.
Yes, I remember those previous discussions. Since they're in the list
archives, I won't argue it any more here. You may absolutely correct, but
you're going to need a rigorous comparative study of some kind to really back
> In my view, it is their stealthy nature that has allowed them to
> flourish.Why do they not make it to islands? Size? Conservative
> dispersal/nestingbehavior? Thinking aloud: the same thing that
> keeps them off the menu on
> the continents also keeps them from long distance/sweepstakes
I wasn't actually making any suggestions on why passerines are diverse but
absent from islands, only that this pattern confounds to some extent (though
not completely) the apparent prevalence of island ground nesters. Of course,
size is a likely candidate.
> > 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 readil y than those with large geographic ranges.
> Yes...more places to hide, more niches to slip into...although, if
> predators have a continental range this should still be limiting on
> specific strategies.
The importance of geographic range in at least modern extinctions seems rather
independent of life history strategy. That is, having a small range makes a
species much more likely to be elliminated by a number of factors. This is
independent of life strategies. I would be quite interested to hear whether
any studies have shown evidence that a wide ranging species was elliminated by
predation alone (or at least primarily). I cannot think of any off the top of
my head, but that doesn't mean it has not been done.