Assignment 3

If vital rates remain constant, what will happen to population structure over time? This question is investigated in the following exercises. Keep in mind that although we are working with a human population model, the same principles will apply for any population of plants or animals.


1 .		Set the number of years to 300 and simulate the population growth of each of the seven nations by using the Population Structure view as described in the previous assignment. Examine the pyramid plots as they change every five years. What happens to each population over the long term? How do the plots differ for each nation? Which nations show the biggest changes over time? Speculate about why these changes occur.

2 .		If a population's age structure stops changing from year to year, demographers say that it has a stable age structure. Two typical patterns of stable age structures are pyramids and inverted pyramids. Compare the stable age structures and intrinsic growth rates of the seven countries. Do you see a pattern? Develop a hypothesis about the relationship between growth rate and the shape of the stable age structure. Test your hypothesis by selecting a nation and altering its fertility rates. Can you create the pyramid and inverted pyramid patterns?

3 .		Choose any country, decrease its 1998 population size based on mortality due to this new strain of HIV, and simulate the population for 300 years. Note: Be sure to change mortality rates for both males and females. What effect, if any, does this have on the long-term age structure? Examine the pyramid plots as they change every five years. Repeat the procedure for alteration in the population structure by decreasing the population of sexually active males and females in the 20-year-old categories. Examine the pyramid plots as they change every five years.

4 .		Formulate a hypothesis to describe how changes (increases and decreases) in fertility rate will affect the long-term population structure. Do the same for changes in female mortality rates. Design and carry out simulations to test your hypotheses.