Essentials of Ecology

S8 SUPPLEMENT 2

Figure 15-3 (p. 373) shows this and other

data in more detail, and illustrates how pie

graphs can be used to compare different groups

of categories and different data sets. Also, see

the Active Graphing exercise for Chapter 15 on

the website for this book.

Questions

1. Do you think that the fact that use of natural
   gas, coal, and oil have all grown over the
   years (see Figures 1 and 2, p. S4) means that
   other categories on this graph have shrunk
   in that time? Explain.


2. Use the projected data in Figure 3 (p. S5)
   to estimate how the relative sizes of the pie
   slices for each energy resource might change
   by 2030.

Reading Maps

Maps can be used for considerably more than

showing where places are relative to one an-

other. They can also show comparisons among

Pie Graphs

Like bar graphs, pie graphs illustrate numeri-

cal values for two or more categories. But

in addition to that, they can also show each

category’s proportion of the total of all measure-

ments. Usually, the categories are ordered on

the graph from largest to smallest, for ease of

comparison, although this is not always the case.

Also, as with bar graphs, pie graphs are generally

snapshots of a set of data at a point in time or

during a defi ned time period. Unlike line graphs,

one pie graph cannot show changes over time.

For example, Figure 12 shows how much

each major energy source contributes to the

world’s total amount of energy used in 2006.

This graph includes the numerical data used to

construct it—the percentages of the total taken

up by each part of the pie. But pie graphs can be

used without the numerical data included, and

such percentages can be estimated roughly. The

pie graph thereby provides a generalized picture

of the composition of a set of data.

Note that in Figure 10, the bars are placed
horizontally and run both left and right from
the center. This allows comparison of two parts
of the population across age groups. In this case,
values for males lie to the left and values for
females lie to the right of the y-axis. The fi gure
contains two separate graphs, one for developing
countries and the other for developed countries.

Questions

1. What are the three largest age groups in
   developing countries? What are the three
   largest age groups in developed countries?
   Which group of countries will likely grow
   more rapidly in coming years?


2. If all girls under the age of 15 had only one
   child during their lifetimes, how do you think
   these structures would change over time?
   Another interesting application of the bar
   graph is called a stacked bar graph. In such a
   graph, each bar is actually a combination of
   several smaller bars representing multiple data
   groups, stacked up to make one bar divided by
   different colors or shades to depict the sub-
   groups. Figure 11 is a good example of this,
   combining population data for six different
   regions of the world. Each bar contains six dif-
   ferent sets of data, all collected in, or projected
   for, a particular year. This bar graph is a power-
   ful illustration of comparative growth rates of
   the human populations in the various regions,
   and it effectively shows the cumulative effects
   of growth.

Questions

1. Which region will likely grow the fastest be-
   tween 2010 and 2050? Which region’s popu-
   lation will likely stay about the same size?


2. About what proportion of the world’s popu-
   lation lived in Asia, Oceania, Africa, and
   Europe (the eastern hemisphere) and what
   proportion lived in North America, Latin
   America, and the Caribbean (the western
   hemisphere) in 2005? How will these pro-
   jected proportions change, if at all, by 2050?

85+

80–85

75–79

70–74

65–69

60–64

55–59

45–49

50–54

35–39

30–34

25–29

20–24

15–19

10–14

5–9

0–4

Age40–44

Male Female

Developing Countries

Population (millions)

300200 100 0 100 200 300

85+

80–85

75–79

70–74

65–69

60–64

55–59

45–49

50–54

35–39

30–34

25–29

20–24

15–19

10–14

5–9

0–4

40–44

Male Female

300 200 100 0 100 200 300

Developed Countries

Population (millions)

Age

Figure 10 Population structure by age and sex in developing countries and developed countries, 2006. (Data

from United Nations Population Division and Population Reference Bureau)

Population in billions

0

1

2

3

4

5

6

7

8

9

1950 1960 1970 1980 1990 2000

Year

2005

2010 2020 2030 2040 2050

North America

Latin America and the Caribbean

Europe

Sub-Saharan Africa

North Arica/West Asia

Asia (excl. W. Asia) and Oceania

Figure 11 Projected world population
growth, by region. (Data from United
Nations)