Re: cause of Gigantism in sauropods

["Alaric Shapli" <alaric7@verizon.net>]

I've heard that bobcats sometimes take down mule deer. A quick web search 
turned up this:

http://www.carnivoraforum.com/index.cgi?board=video&action=display&thread=4601


-----Original Message----- 
From: Habib, Michael
Sent: Monday, February 07, 2011 1:11 PM
To: vultur-10@neo.tamu.edu
Cc: dinosaur
Subject: Re: cause of Gigantism in sauropods


On Feb 7, 2011, at 12:45 AM, <vultur-10@neo.tamu.edu> wrote:

> > >
>
> So in the Morrison, the sauropod-theropod size gap seems smaller than the 
> elephant-lion one. I see little reason to believe that Saurophaganax or A. 
> maximus could not take down even Giraffatitan or Supersaurus.

Neat comparison with the body mass estimates (thanks for punching the 
numbers!) but I'm not sure I quite agree with your conclusion.  It seems 
reasonable that something like Saurophaganax could take down something like 
Giraffatitan under very rare, extreme circumstances, just as living 
terrestrial macro-predators (or groups of them) very rarely kill much larger 
animals than themselves.  However, I see no reason to expect that such 
events were common, or even occurred with a high enough frequency for us to 
seriously consider them as major factors in our  reconstructions of Mesozoic 
ecology.  Living terrestrial vertebrate predators rarely take prey even 
three times their own mass, much less 6-8 times.

The elephant-lion size ratio probably does not represent the ratio at which 
predation is regular or ecologically important; at best it is a ratio at 
which a very rare predation event is still barely feasible - and that is for 
a specific guild of predators and herbivorous mammals.  The more important 
size ratio is the maximum predator:prey mass ratio among *regular* predation 
events.  Phrased as a question: Of those large terrestrial animals that are 
predated as adults with a high enough frequency for its impact on total 
population mortality to be measurable, how large are their smallest 
predators (or total mass of packs, if they are predated by groups)?

I don't know exactly what the answer to that question is, but qualitative 
observation suggests that the size gap is pretty small.  The vast majority 
of predators, even large ones, mostly take prey smaller than themselves. 
Even animals like water buffalo, which are a fraction of the size of 
elephants, are large enough as adults to be predated upon rarely (albeit 
more often than elephants).

Cheers,

--Mike


Michael Habib
Assistant Professor of Biology
Chatham University
Woodland Road, Pittsburgh PA  15232
Buhl Hall, Room 226A
mhabib@chatham.edu
(443) 280-0181