Simulation of Population Growth

by Janice Anderson
Adapted from Center for Occupational Research and Development

 Background Method Purpose Conclusion Materials For more information Objectives Return to lesson plan index

Background
Think about the changes that have occurred in the community in which you live during the past few years. Previously unpaved roads may have been paved. Shopping centers, homes, and apartment buildings may have been built. Previously undeveloped areas have become developed.

As the human population expands into areas that were previously left for wildlife, the available habitat for wildlife decreases. We therefore need to consider what is gong on with the human population to appreciate what effect it will have on the other species around it.

The growth rate of a population is determined by the difference between its birth rate and its death rate. If the birth rate remains constant, but the death rate declines, the population will increase. If the death rate remains the same, but the birth rate increases, the population will also grow. Any increase in the size of the human population will affect the demand for space, water, food and other necessary resources, and will compete with other organisms that need the same resources.

Many of the environmental problems that we face are the result of rapid growth of the human population. If the birth rate and the death rate are equal, the population will stay about the same over time, causing the demand on vital resources for humans to also remain the same.

Purpose
In this activity, students will model three patterns of human population growth. The simulation will involve the use of specifically-colored cubes to conduct the simulation.

Materials
Advanced Preparation by Teacher
1 cm by 1 cm (or 2 inch by 2 inch) trim strips can be purchased from a lumber supply store. One side of the strip should be painted white, and one side should be painted green. The number of strips purchased will depend on the number of students groups planned. Once the paint is dry, the strips should be cut into cubes and put into empty two-pound (or three pound) coffee cans.

250 colored cubes per group
coins
coffee cans
wood strips
graph paper
white paint
colored pencils
green paint

Objectives
1. In this lab, students will simulate the growth of three populations over a period of 10 years.
1. A population of a typical underdeveloped nation.
2. A population of an nation in which birth control is practiced.
3. A nation with zero population growth.
2. Students will graph data and interpret growth rates from the graph.
3. Students will predict the future growth of the population growth from the data collected.
4. Students will predict the environmental effect of increased population growth.

Method

1. Students are divided evenly into groups, with an equal number of groups doing Simulation A, Simulation B, and Simulation C.

2. Each group will be given a coffee can containing 250 cubes with colored faces.

3. Members of each group will follow the instructions that specifically apply to their group.

Simulation A

1. Place 20 colored cubes in your can. Keep the rest of the cubes separate as your stockpile.

2. Record 20 as the population size for year 1 of the study.

3. Shake the can while holding it upright, and empty all of the cubes onto the lab table.

4. The color of the face of the cube facing upwards, determines what should be done with that cube.

• If the black face is facing up, that individual has died. Remove all black cubes from your population, and return them to your stockpile. Record the number of either in the data table.
• White or green faces represent females that have borne a child in that specific year. Count the number of white and green faces and add that number of cubes to your population.
• Record the number of births in the same row as you recorded the number of deaths for that year.
• Those with uncolored faces represent males and/or females who have not produced a child in that particular year.

5. Count the total number of cubes now on your lab table, and record this number in your data table in the same row as for other data for that year.

6. Return all cubes in your current population to the can.

7. Repeat steps 3-6 for 9 more years.

8. Return all cubes to the can, and plot the population growth for your population with a colored pencil, with years on the horizontal axis, and size of the population on the vertical axis.

Simulation B

Follow directions for Simulation A with the following exceptions:

• Black cubes represent individuals that have died. Count them and remove from your population, and return them to the stockpile.
• White cubes represent a female who have just borne a child. These should be counted, and for each white cube, add one more cube to your population from the stockpile.
• The cubes with green faces up represent a group of individuals in which only half of them bear a child. The other half are females who successfully have practiced birth control. Count the number of green cubes and divide by two. Also add this number of cubes to your total population. If there is an odd number of green cubes, flip a coin (heads=yes, tails=no) to determine whether or not the extra "green" female bears a child.
• All uncolored faces represent males in the population or females that are either not within the child-bearing years, or those who have not borne a child for some other reason.

Simulation C

Follow the directions for Simulation A with the following exceptions:

• Black cubes represent individuals that have died. They should be counted and removed from your population.
• White cubes represent a female who has successfully borne a child. These should be counted, and for each white cube another cube should be added to your population from the stockpile.
• A green cube represents a female who is successfully practicing birth control.
• Uncolored cubes are representatives of males or other non-reproducing females.

Results

Record all data in a table such as this.

 Year Number of Births Number of Deaths Population Size 2020 2021 2022 2023 2024 2025

Conclusion

1. Calculate your population's annual growth rate for the last year of your data table. Use the following formula:

Annual Growth Rate (%) = Population size in chosen year - Population size in previous year x 100 = Population size in previous year

2. To find the doubling time in years for your population, divide the Annual Growth Rate (%) into 70. This number represents the number of years it would take for your population to double.

3. Compare the doubling time for each of the simulated populations. Give an example of a country that has a growth rate similar to each of the populations simulated.

4. Collect data from each of the simulated population types. Add the data for each type of simulation to the same graph on which you have already shown the results of your own simulation. Be sure to use a different colored pencil for each simulation. Label each line.

5. Within your group, brainstorm to create a list of as many environmental effects you can think of for increased human population size.

6. Recent research results of United Nations studies on growth trends of human population world-wide.

7. Discuss the following question within your group, and write out your general conclusions.

Do better economic conditions cause a decrease in the birth rate, or is it a decrease in the birth rate that causes improved economic conditions?