8

Population: Measuring

Growth and Its Impact

Chapter Outline

The Growing Human Population

Why Has the Human Population Grown So Large?

Expanding the Earth’s Carrying Capacity

What is the Earth’s Carrying Capacity for Humans?

Too Many People, Reproducing Too Quickly

Understanding Populations and Population Growth

Measuring Population Growth

Total Fertility Rate and Replacement -Level Fertility

Migration

Population Histograms

Exponential Growth

The Future of World Population: Some Projections and Concerns

Key Terms

population growth carrying capacity infant mortality

overpopulation growth rate crude birth rate

crude death rate doubling time total fertility rate

replacement-level fertility zero population growth migration

immigration emigration internal migration

exponential growth population histogram sigmoidal

Objectives

1. Discuss why the human population has grown so large.

2. Define “carrying capacity.”

3. Discuss the impact of overpopulation on our environmental problems.

4. Define the following terms: “growth rate,” “crude birth rate,” “crude death rate,” and “doubling time.”

5. Compare the population growth rates of developing and developed nations.

6. Define “total fertility rate” and “replacement-level fertility.”

7. Discuss why population size in the United States continues to grow even though the replacement-level fertility rate has been reached or exceeded.

8. Define “migration,” “immigration,” “emigration,” and “net migration.”

9. Discuss the pros and cons of immigration in the United States.

10. Describe a population histogram and explain its use in understanding the demography of a population.

11. Draw an exponential growth curve and a sigmoid curve.

Lecture Outline

The Growing Human Population - Currently, the world population is 6.4 billion; 83 million people are added yearly.

A. Why Has the Human Population Grown So Large?

1. The Survival Boom - The phenomenal upsurge in population growth in modern times is due to two factors: slightly increased reproduction rates and dramatically decreased death rates, which have contributed to a higher average life expectancy.

B. Expanding the Earth's Carrying Capacity - The maximum population an ecosystem can support sustainably is termed the carrying capacity.

2. Advances in tools, agriculture, medicine, and technology have enabled humans to increase the earth's carrying capacity.

3. While necessary to provide for an expanding human population, such increases invariably result in increased depletion and pollution.

C. What is the Earth’s Carrying Capacity for Humans? - Accurate estimates of the earth's carrying capacity for humans are difficult due to the variables of affluence and technology. Many people think that the human population already exceeds the Earth’s long-term carrying capacity, creating an unsustainable condition.

D. Too Many People, Reproducing Too Quickly - Overpopulation is at the root of virtually all environmental problems, including pollution and resource depletion, and many social and economic problems. The results are:

1. Urban despair caused by overpopulation.

2. Rural despair caused by overpopulation.

3. All of the social, economic, and environmental problems are exacerbated by rapid growth. Efforts to solve these problems are hampered by rapid population growth.

Understanding Populations and Population Growth - Demography is the study of population statistics and characteristics.

A. Measuring Population Growth

1. Growth Rate - Growth Rate (%) = (Crude Birth Rate - Crude Death Rate) x 100

2. Birth Rates - Birth rates for any population are influenced by age of marriage, educational level, contraceptive use, female employment, and couples' desires, beliefs, and values.

3. Death Rates - Rapidly falling death rates due to improved living conditions and medical treatment have caused an increase in population growth rate in the past century.

4. Doubling Time - The formula for doubling time is: DT = 70/GR(%). At the current growth rate of 1.8%, developing nations will double in about 33 years. Growth rates in developing countries on average far exceed those of developed nations.

B. The Total Fertility Rate and Replacement-Level Fertility

1. The Total Fertility Rate (TFR) is the average number of children a woman will bear.

2. Replacement-level fertility is reproduction at exactly that level necessary for couples to replace themselves.

3. Due to immigration and momentum from the lag effect, most populations will not reach zero population growth immediately upon reaching replacement reproduction.

C. Migration - Migration is the number of individuals moving in a population. Migration has two forms, immigration (movement into a country or system) and emigration (movement out of a country or system).

1. Net migration is immigration minus emigration.

2. Zero population growth for any population can only be reached when growth rates and net migration rates are zero.

3. Intranational or internal migration has had profound demographic, as well as economic and environmental, effects in the U.S.

D. Population Histograms - Histograms are graphic representations of the age structure and gender distribution of a population. Shifts in population structure can signal dramatic changes in the economic, employment, infrastructure, and healthcare needs of a population.

E. Exponential Growth

1. Growth at a fixed yearly rate is exponential.

2. When graphed, exponential growth can be seen to start slowly, then round a bend to enter a phase of increasingly rapid growth; if unchecked, an overshoot may occur. Resource recovery and pollution assimilation cannot keep up with the rapid growth in human population.

The Future of World Population

A. Estimates of maximum human carrying capacity range from 500 to 1000 billion; it may then level off, decrease slowly, or drop dramatically, depending on many variables.

1. No finite system can accommodate infinite population growth.

B. Why should we worry about population growth in developing nations?

1. Illegal immigration into the United States.

2. Increased political strife in the Middle East and elsewhere.

3. Growing international population increases the production of food for export. This places additional stress on our already unsustainable agricultural system.

4. Expanding world population results in destruction of habitat and loss of valuable species.

5. Population growth exacerbates global warming.

6. The cycle of poverty is revisited in developing nations.

Suggestions for Presenting the Chapter

· The instructor should stress that many of the world’s problems have their root in population size. Overpopulation affects every part of our lives.

· A speaker on family planning will provide interesting topics for class discussion.

· The instructor should emphasize that although developing nations are not growing rapidly they still have population concerns because of the per capita impact of individuals in these countries.

· Computer software for modeling population dynamics is available. Exposing students to these programs is an effective tool for teaching concepts in this chapter.