This program uses mathematical modeling to explore the concept of population equilibrium, using data gathered about the blue whale. Birth and death rate combinations charted on a line graph illustrate how each affects population equilibrium. Population counts are shown to drop below minimum sustainable levels when environmental and human factors, such as overhunting, are introduced. When this occurs, animals are unable to replenish themselves and the species becomes extinct. Scientists and mathematicians stress the importance of mathematical modeling as a predictive tool, and discuss how the information can be used by wildlife managers to prevent extinctions. Produced by the Open University. (25 minutes)