Re: [Re: [Endotherms and island life (was: follow-up on sauropods)]]

[archosaur@usa.net]

jbois@umd5.umd.edu wrote:
> 
> 
> On Sun, 7 Jun 1998 archosaur@usa.net wrote:
> 
> > Sure it makes sense for a small to medium animal to get
> > big in the absence of competition. Competition is what
> > supposedly kept them small in the first place. 
> > 
> > On the other hand if your huge and on an island then maybe
> > it would make more sense to shrink your size some, so as
> > not to eat away house and home.
> 
> I'm not aware of any evidence for your hypothesis that large size in
> tortoises, dragons (and birds!) on islands is due to release from
> competition. 
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That's right. I forgot all about Moas. Well that kills
the metabolism hypo.

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 We had a discussion here about a month or so ago which
> flagged our tendency to invoke competition as the only or prime force in
> structuring communities.
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Sorry I missed it. Also 99% of all life is extremely small.
This seems to suggest that being small is selected for more
often than being large, but that's kind of off topic.

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  An equally robust hypothesis for the increase in
> size of oviparous species on islands is their release from predation--and
> since these forms seem to relatively free of predation on their adult
> stages, I mean predatiion on eggs or hatchlings.  In short, it is possible
> that oviparous species get big because they are released from the dreaded
> mammal.
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I kinda follow and yet I kinda don't. Reptiles and 
birds play just as an important role as mammals when it
comes to egg thievery. Varanids are notorious egg eaters
and are the major predator of reptile and bird eggs in Australia 
and I think Africa too. One form of snake took to a completely egg eating 
existence. 

Also, the largest reptiles today, the crocodilians all are oviparious and are 
just plain huge. So I don't think a release from egg eaters would have done it. 
I guess competition wouldn't either.

I know what would though. unfilled niches. Whenever there is a niche that is 
not filled something comes along to fill it. Little monitors 
going to Komodo, found all kinds of large animals that had no
predators and they took advantage of it by taking over that niche. 

Same thing for turtles and iguanas on the Galapagos. Maybe that 
is what makes small animals big?

Archosaur J

"Well theres a hypothesis. Now how to prove it?"


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