Look at the BioQUEST program called Demographics, written by Dan Udovic
and friends, which lets students play with different demographic
variables to see what would happen to population size and structure
over time. There are other programs around which might be relevant as
well, for a partial list you could look in my Biology Education
Software FAQ released to this group periodically, or download it from
ftp.zoology.washington.edu /pub/doc/
Eli Meir
Dept of Zoology, Univ of Washington
meir at zoology.washington.edu