Visualizing Environmental Science

Summary 187

the same size because the birth rate equals the death rate,

toward the end of the 21st century.

2. Thomas Malthus was a British economist who said that
   the human population increases faster than its food supply,
   resulting in famine, disease, and war. Malthus’s ideas appear
   to be erroneous because the human population has grown
   from about 1 billion in his time to 7 billion today, and food
   production has generally kept pace with population. But
   Malthus may ultimately be proved correct because we don’t
   know whether our increase in food production is sustainable.


3. Estimates of Earth’s carrying capacity for humans vary widely
   depending on what assumptions are made about standard
   of living, resource consumption, technological innovations,
   and waste generation. In addition to natural environmental
   constraints, human choices and values determine Earth’s
   carrying capacity for humans.

3

Demographics of Countries 170

1. Demographics is the applied branch of sociology that
   deals with population statistics. As a country becomes
   industrialized, it goes through a demographic transition
   as it moves from relatively high birth and death rates to
   relatively low birth and death rates.


2. The infant mortality rate is the number of deaths of infants
   under age 1 per 1000 live births. The total fertility rate (TFR)
   is the average number of children born to each woman.
   Replacement-level fertility is the number of children a
   couple must produce to “replace” themselves. Age structure
   is the number and proportion of people at each age in a
   population. A country can have replacement-level fertility and

Summary

1

Population Ecology 160

1. Population ecology is the branch of biology that deals with
   the number of individuals of a particular species found in an
   area and how and why those numbers change over time.


2. The growth rate (r) is the rate of change (increase or decrease)
   of a population’s size, expressed in percentage per year. On
   a global scale, growth rate is due to the birth rate (b) and
   the death rate (d): r = b – d. Emigration (e), the number of
   individuals leaving an area, and immigration (i), the number
   of individuals entering an area, also affect a local population’s
   growth rate.


3. Biotic potential is the maximum rate a population could
   increase under ideal conditions. Exponential population
   growth is the accelerating population growth that occurs
   when optimal conditions allow a constant reproductive
   rate for limited periods. Eventually, the growth rate
   decreases to around zero or becomes negative because
   of environmental resistance, unfavorable environmental
   conditions that prevent organisms from reproducing
   indefinitely at their biotic potential. The carrying capacity
   (K) is the largest population a particular environment can
   support sustainably (long term) if there are no changes in
   that environment.

2

Human Population Patterns 165

8000 6000 4000 2000 0 2000

BCE CE

Time (years)

Human population (billions)

1

2

3

4

5

6

7

2011: 7 billion

Black Death

1. It took thousands of years for the human population to
   reach 1 billion (around 1800). Since then, the population has
   grown exponentially, reaching 7 billion in late 2011. Although
   our numbers continue to increase, the growth rate (r) has
   declined slightly over the past several years. The population
   should reach zero population growth, in which it remains

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Alberto Ceoloni/ZUMAPRESS/Newscom