Chapter 15 Human Ecology • MHR 507Country or regionProjected
population 2025
(millions)Projected
population 2050
(millions)
World
less industrialized
nations (average)
Uganda
Costa Rica
Turkey
more industrialized
nations (average)
Canada
United States
Norway7818
6570
48
5
85
1224
36
346
5
9036
7794
84
5
97
1242
36
413
5
Table 15.2
Approximate fertility rates, projected population sizes, and other parameters
for selected countries and regions (from the Population Reference Bureau)Infant mortality
rate in 2001
(deaths per 1000
live births)Total
fertility
rate in
2001
56.061.097.0
12.0
35.08.05.5
7.1
3.92.8
3.2
6.9
2.6
2.5
1.6
1.4
2.1
1.8
Percentage of
population less than
15 years of age in
2001
303351
32
301819
21
20Demographic Transition and
Population Age Structure
Human demographers tend to refer to the average
number of children born alive to each woman in a
population during her lifetime as the fertility rate
rather than as the rate of fecundity. The latter term
is more commonly used by ecologists working with
other types of organisms (see Chapter 14, section
14.4). The fertility rate required to achieve long-
term zero population growth is called the
replacement fertility rateand is 2.1 children per
woman. This rate is just enough to replace the
parents who produced them and to compensate for
children who die before reaching reproductive age.
Countries that have completed their
demographic transition (or that are in Stage 3) have
declining birth rates. In fact, they have fertility rates
at replacement level or below. Both of these rates
have been dropping substantially in recent years,
causing demographers to re-adjust earlier projections
of the future size of the human population.
According to the United Nations Population
Division, 44 percent of the world’s population
lived in countries with fertility rates at or below
replacement level in 1995. Only a few of the less
developed nations had shown no signs of fertility
reduction, and the fertility rates of 49 nations
(including China, which comprises about one
fifth of the world’s population) had been below
replacement level for over a decade.
Some countries, however, still have fertility rates
above replacement level. As a result, the global
average fertility rate in 2001 was approximately
2.8 children per woman per year. If it stays at this
level, world population is projected to reach
7.82 billion in 2025 (see Table 15.2). Many
demographers predict that the worldwide average
fertility rate may decline further to reach 2.1 by
2050 as more countries progress through the
demographic transition. If this happens, they
estimate that the human population will stabilize
at just under 10 billion by 2150. However, if the
average fertility rate is higher or lower than this in
2050, the projected population could be quite
different, as shown in Figure 15.4 on page 510.
Notice that although the difference between the
high and low fertility rates in Figure 15.4 is only
about one child per couple, it can alter the
projected population sizes quite dramatically.
Note that just because the fertility rate of a
country or region has reached replacement level,
it does not mean that the population will stop
growing (that is, that it has reached zero population
growth). There are other factors to consider as well.
For example, infant mortality varies among
countries and will alter the rate of growth. Notice
also that there is variation in the proportion of
young individuals in the populations listed. In
Chapter 14, you saw that the birth rate not only
depends on the number of offspring each female
has, but also on the number of females available to
have young or the number of females who will be