Introduction to Environmental Science, 2nd Edition, 2018a

Figure 3.1: Shows the increase in human population size starting in 1750 and predicted out to 2050. The
orange area represents the human population in industrialized countries and the blue/green area represents the
human population in less-industrialized (developing) countries. The greatest amount of human population
growth will be in less-industrialized countries.
3.2 Demography
Demography applies the principles of population ecology (chapter 2) to the human population. Demographers
study how human populations grow, shrink, and change in terms of age and gender compositions.
Demographers also compare populations in different countries or regions.
3.3 Age structure diagrams
One of the tools that demographers use to understand populations is the age structure diagram. This diagram
shows the distribution by ages of females and males within a certain population in graphic form. Figure 3.2
shows a diagram for the United States population. In this diagram, the ages are arranged so that age ranges are
grouped together, for example: 0 – 4 years, 5 – 9 years, and so on. The population of each group is represented
as a bar extending from a central vertical line, with the length of each bar dependent upon the total population
for that particular group. The centerline separates the females from the males. The female and male populations
for each group are represented by the distance from the centerline, with females on the right and males on the
left.
2