Re: ...bats by day, and bats, birds, by night.

[John Bois <jbois@umd5.umd.edu>]

> On Monday, July 15, 2002, at 12:00  PM, John Bois wrote:
>
> > Outside of catastrophies (which you're not invoking) competition and
> > predation are the prime causes (most likely) of most extinctions.

To which HP Conway replied:

> What about changes in the environment, extinction of a food source etc.?
> Ecologies are VERY complicated systems, with many interdependencies. The
> kind of direct competition and predation you seem to be talking about
> may not have much to do with many extinctions.

Well, I don't see _anything_ simple about competition and/or predation.

> > What do you think
> > could have driven these species into extinction?
>
> Changes in the environment, extinction of a food source, ect. There are
> many, many things that can cause extinction at the species level - few
> that can cause the extinction of very large clades.

But my understanding is that you need a force that knocks out large clades
before the bolide.

> >  I think what we are seeing is a kind of niche partitioning:
> > birds are better competitors at some times, and bats at others.  And, I
> > would be surprised if predation avoidance in birds wasn't part of that
> > equation.
>
> We seem to be seeing competitive exclusion working rather powerfully,
> and you seem to agree. Birds would have faced a similar situation in
> trying to compete with pterosaurs (if they did).

Competitive exclusion is defined as one species so completely outcompeting
the other that they become locally extinct.  Not the case in birds and bats.
What they are doing is partitioning the resource (e.g., insects).  Just as
Anolis lizards famously divvy up upper and lower branches, bats and birds
split the niche temporally.  And, there _is_ some overlap.  This definitely
rules out competitive exclusion.  Bats and birds have not competitively
excluded each other.  On the other hand, birds _may_ have competitively
excluded pterosaurs.

> > 1) Most pterosaurs became extinct from causes other than the bolide.
>
> True, but then so did most dinosaurs, and any other clade you might want
> to mention, because only a small percentage of large clades is extant at
> any one time.

What I meant was there was a great reduction in pterosaur diversity caused
by forces other than the bolide.

> > 2) No pterosaurs handed over their niche as a gift to rising new
> > species.
>
> ? Maybe as pterosaur species became extinct from other causes (see
> above), new species of birds filled the gaps (as they reopened) than new
> pterosaurs.

What other _global_ forces could do this?

> > 3) Something forced them out of their niche.
>
> Depends what you mean by "forced". Birds may, I repeat, may, have been
> able to speciate faster than pterosaurs. As pterosaurs became extinct,
> birds filled the niches faster than pterosaurs, but this didn't
> necessarily have anything to do with direct competition or predation.

Not sure I understand: I thought you were saying that pterosaurs had
first dibs on their niche and could not be budged through competition.  Now
you're saying new bird species bumped them out.  How do they do this?

> > 4) The most likely things to do this is are flying creatures.
>
> Many pterosaurs ate fish, and for this resource  they competed with
> other fish and swimming reptiles, neither of which fly.

I like it.  But does it explain _most_ extinctions--were most fisheaters?

> Pterosaurs
> nested on land (or in trees?), in both places lived predators such as
> non-avian small theropods, lizards, and mammals, none of which fly.

I think pterosaurs would have been limited to offshore islands, or otherwise
inaccessible places.  I can't see a pterosaur defending against a dino.
Maybe trees.

> Why did this process take so long? If birds were better competitors, why
> did they take tens of millions of years to out-compete pterosaurs? One
> would expect such direct competition to remove pterosaurs much faster,
> probably just a few million years. Maybe less.

Because birds became better competitiors.

> I agree with DM that competitive exclusion has a very
> important part to play.

Yes.  Birds competitively excluded pterosaurs, i.e., they became extinct and
birds didn't!  Now, how did it happen?