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Re: pterosaurs, bats, flying theropods (fwd)



> ---------- Forwarded message ----------
> Date: Fri, 27 Dec 2002 16:41:52 -0500
> From: Michael Bruce Habib <mbh3q@virginia.edu>

> Those bats that forage diurnally probably are secondarily
> diurnal.  That is, nocturnality is probably plesiomorphic;
> some bats have derived diurnal habits, and this is then
> repressed if raptors show up (unless the bats are large).

OK.

> There is no evidence I know of to show that bat species
> present before the divergence of raptors had a higher
> degree of diurnality than later species.

Why can't it just be a fundamental/realized niche phenomenon.  I don't see
anything _intrinsic_ to the animals to make them one way or another for all
time.  I agree with you that different traits provide different advantages.
But there is no reason to assume bats wouldn't take over in the day time if
other things weren't preventing them in some rigorous way.  My argument is
that competition for food is not a likely reason, simply because birds and
bats are both very effective at exploiting available resources.

> I see the difference in sensory equipment and flight styles
> as being the most important factors keeping most birds
> diurnal and most bats nocturnal.

Me, too.

> The average flight speeds
> of birds are quite a bit higher than those of bats.

Enabling escape from predation, perhaps.

> This has certain obvious advantages, and works fine IF an
> animal is visually-based.  Light-based vision has good
> range and excellent resolution. Of course, it doesn't work
> very well at night.

Enabling slower fliers a margin for existence.

> Keep in mind that bats do not only have ecolocation, they
> have _fantastic_ hearing in general, ( at high frequencies,
> anyway) which is paramount for good night feeding.

Yes.

> Also keep in mind that raptors do not need to eat bats into
> nothingness to keep them nocturnal; they simply have to be
> good enough at it to give nocturnal bats an advantage over
> diurnal bats.  It's really competition within bats that
> keeps them nocturnal, after all.

I'm reminded of the different levels of self as proposed by, say, Dawkins
(the selfish gene), and Lovelock (Gaia-wherein the unit of self is the
planet).  As with so many things in biology, there are many true ways of
looking at things.  I agree with your take on it--bats v other bats.  I also
think bats are in competition with birds but are losing as long as they
suffer more intense predation.  But the agents that arbitrate these
competitions are very different for bats v. bats, versus bats v. birds.