Popular Pyramids: Age Structure Diagram Activity

Background:Population growth is affected by age structure - the number of individuals in different age groups - as well as by the numbers of births and deaths. Age structure is usually illustrated by an age pyramid, a graph in which horizontal bars represent the percentage of the population in each age group. Males are shown on the left and females on the right. The ages (or in some cases, the years of birth) for each bar are listed along the vertical axis of the graph, usually in five-year intervals. Each age group is called a cohort. The longer a bar is, the greater the proportion of individuals in that age group.

Age pyramids are useful for tracing the history of a population and for projecting future population trends. An age pyramid with more long bars for the younger age groups would indicate a growing population; when these large numbers of young begin to reproduce; they will add even more offspring to the population than did the older age groups.

Directions: Using the table below, construct an age structure diagram for both the United States and Rwanda. Graph the countries separately. Make sure you use different color pencilsfor each gender (male or female) and to label the axes. Then answer the questions listed below the data table.

Data Table:

United States / Rwanda
% age / Male / Female / % age / Male / Female
0-4 / 3.2 / 2.9 / 0-4 / 7.4 / 7.6
5-9 / 6.5 / 3.1 / 5-9 / 7.2 / 7.4
10-14 / 3.2 / 2.9 / 10-14 / 7.0 / 7.0
15-19 / 3.2 / 3.2 / 15-19 / 6.0 / 6.0
20-24 / 3.0 / 2.5 / 20-24 / 4.2 / 5.4
25-29 / 2.9 / 2.9 / 25-29 / 3.2 / 2.7
30-34 / 3.1 / 3.2 / 30-34 / 2.8 / 2.8
35-39 / 3.7 / 3.7 / 35-39 / 2.2 / 2.2
40-44 / 3.7 / 3.7 / 40-44 / 1.8 / 2.0
45-49 / 3.2 / 3.2 / 45-49 / 1.3 / 1.5
50-54 / 2.8 / 2.8 / 50-54 / 1.8 / 2.0
55-59 / 1.9 / 2.2 / 55-59 / 0.6 / 0.7
60-64 / 1.7 / 2.1 / 60-64 / 0.5 / 0.5
65-69 / 1.5 / 2.0 / 65-69 / 0.5 / 0.4
70-74 / 1.3 / 1.9 / 70-74 / 0.4 / 0.3
75-79 / 1.2 / 1.7 / 75-79 / 0.3 / 0.2
80+ / 0.7 / 0.8 / 80+ / 0.2 / 0.1

Analysis Questions: Please use complete sentences.

1) What are some overall similarities between the two (2) graphs?

2) What are some differences?

3) What do you believe the increased population size in the United States between ages 35-40 is due to?

4) The female population in Rwanda makes a shark drop between ages 20-24 and 25-29. What do you think accounts for the drop in this percentage?

5) What does the age structure diagram tell you about these countries?

6)Which country has the highest percentage of older population? Why?

7) Is the U.S. population increasing, decreasing, or remaining the same? How do you know? (think about the proportion of older vs younger people)

8) Is the Rwanda. population increasing, decreasing, or remaining the same? How do you know (think about the proportion of older vs younger people)?

9) Based upon the evidence in the age structure diagram, do you think the human population will reach a carrying capacity? Explain.