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RE: Determinant of dinosaur fecundity?



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From:  John Bois [SMTP:jbois@umd5.umd.edu]
....

I agree with the latter assumption but not the former.  For example, how
can we know what the cost of nest defence was?  Take a broader view of
reproductive burden (beyond definition, perhaps).  Truly, the size of
a dinosaur is "of no selective value except inasmuch as it contributes to
that organisms lifelong production of successful offspring" (from Pianka,
_Evolutionary Ecology_, who was not talking about dinos but all
organisms).  These issues should be included in th3e overall costs of
reproduction.

There are many things that might contribute to the cost of reproduction - 
including behavioral things like nest building or defense.

The direct biological cost is the energy it takes to make the offspring 
(eggs or live young).  This depends both on the offspring, and the 
gestation time.   In many animals this is a very significant resource drain 
on the female, so only females in good health and with a very good food 
supply should attempt to reproduce.  Even so, the direct biological cost 
can put the female in danger.

This does not appear to be the case with dinosaurs, especially the larger 
ones.  Their clutches are tiny by any measure when compared to the size of 
the adults.   So the direct biological cost is very low.   As a result, 
dinosaurs probably laid eggs every year.

It is possible that there were other indirect factors.  However, an 
argument can be made that given a fairly low investment in a given clutch, 
that there is no evolutionary reason for the parents to invest a great deal 
in behaviors to protect it.

Nathan