[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: Determinant of dinosaur fecundity?



>-----Original Message-----
>From:  John Bois [SMTP:jbois@umd5.umd.edu]
>Sent:  Thursday, January 30, 1997 3:50 AM
>To:    dinosaur@usc.edu
>Subject:       Determinant of dinosaur fecundity?
>
>
>More than a rhetorical question: Is this relevant to dinosaurs (from T.
>Martin (Biosciwence Sept '93) "Recent interspecific studies demonstrate
>that adult survival varies inversely with fecundity in both Europe and
>North America."
>[Nathan Myhrvold]  
>
Probably not.    

Fecundity is usually measured as number of offspring produced per female
per unit time.

Many animals with high fecundity also have low survival rates (as both
juvenile & adult).  Animals with this reproduction strategy are known as
r-strategists.   Most insects, rodents take this approach.  Many other
animals (particularly large ones) with low fecudinty have high survival.
  As an example, elephants produce one offspring every 3 years, but they
can live up to 50 or 60 years in the wild.  This reproduction strategy
is called being a K-strategist.

The inverse relationship you mention is inherent in these descriptions.
However, there is no law that says an animal must be at one extreme or
another.   Crocodillians today straddle the fence - they have high
fecundity and lay very large clutches of eggs each year (20 to 50), but
can live to 50 years or more as adults so their adult survivorship is
also high.  No inverse relationship here.  They suffer very high
juvenile mortality, but once they get a certain size life gets a lot
less risky.

Dinosaurs appear to also have been in this middle ground.  Fossilized
nests have shown they have typically around 20 eggs.  Given the size of
the eggs relative to the mass of the female, even this many eggs it is a
very low reproductive burden (it's cheap to make them), so we could
assume that the laid them annually.   On the other hand, the huge size
of most dinosaurs suggests that many species had long lives up to 50
years and possibly 100 or more for the large sauropods (see recents
posts by Greg Paul), which means that adult surviorship had to be very
high.

Nathan

>