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group hunting (was Scavenger vs. Predator Argument)



Jack Conrad wrote:

>                                                               ...It
>should also be noted that lionesses do the majority of the hunting in the
>species because the males have biological barriers (i.e. heavy mane) which
>degrade their ability to actively hunt somewhat (though solitary males or
>brothers do hunt effectively when they are without a pride)...

IIRC, male lions in a pride often flush prey towards hidden lionesses, but 
rarely bring down animals themselves.  This may be because they aren't so 
effective at hunting per se, but it may be because they lack lionesses' 
skills in group hunting.  Or they may simply not want to risk injury, 
knowing that because they're bigger they can claim the lion's share of the 
kill anyway.  If you are trying to panic prey, a conspicuaous mane may be an 
asset. 

>                                                           ...We have no
>evidence that male tyrannosaurs had similar hindrances, but there can be
>no evidence that they did not either.  This means that the sex of the
>rex is irrelevant (unless you are a rex) as far as hunting goes...

The gracile and robust morphs probably represent different sexes, and the 
robust ones are probably females.  I would guess the difference in size and 
strength was similar to that in lions, but with the females bigger.  I'm 
sure someone on the list is familiar enough with both to correct me.

Speculating beyond the evidence, it's possible that T. rex males formed 
prides led by one or a few females.  The strong females would defend 
territory, but the faster and stealthier males would make more effective 
hunters.  

T. rex presumably laid numerous eggs which produced small hatchlings, so the 
breeding potential of a group would depend more upon the number of males 
supplying meat than the number of females laying.  This is one situation 
where a polyandrous mating system is evolutionarily possible, but it is 
possible that only a few of the strongest males mated.  The others would 
have to be closely related to make it worth their while to hunt.

If young males stayed with their natal pride, they would probably be too 
weak at first to have access to the breeding females.  They would be able to 
help raise younger siblings, half-siblings, cousins, etc..  In such a 
situation, it becomes advantageous to produce sons rather than daughters.  
Sons will expand their parents' breeding potential, while daughters will 
grow up to threaten the group.

Armed with this theory I predict a strongly male-biased sex ratio in T. rex.  
And sure enough, there is.  It also explains why Sue suffered more injuries 
than males: fighting between females over the large resources of a pride of 
males would be much more serious than a squabble between closely related 
males over how many times each will mate with one female.

I won't be surprised if this is shot down in flames.

                                                        All the best,

                                                                        Bill