Chapter 11Chapter 11

Human Population:Human Population:Growth, Demography, & Growth, Demography, &

Carrying CapacityCarrying Capacity

tutorial by Paul Rich

© Brooks/Cole Publishing Company / ITP

OutlineOutline

1. Factors Affecting Human Population Sizebirth & death rates

2. Population Age Structureage structure diagrams, developing vs. developed countries

3. Solutions: Stabilizing Human Populationcomputer models, demographic transition

4. Case StudiesUnited States, India, China

5. Human Population & Sustainability

© Brooks/Cole Publishing Company / ITP

1. Factors Affecting Human Population Size1. Factors Affecting Human Population Size

• Human population is currently growing exponentially.

• What will be the ultimate size of the human population?

• What is Earth's carrying capacity?

Factors Affecting Human Population SizeFactors Affecting Human Population Size

Population change is calculated as the difference between individuals entering and leaving a population:

birth rate is reported as the number of births per thousand people;

death rate is reported as the number of deaths per thousand people;

zero population growth (ZPG) occurs when factors that increase and decrease population size balance.

Population ChangeBirths

+Immigration

Deaths+

Emigration–=

Rule of 70

Simply stated, the "rule of 70" says that the number of years it takes for an amount growing at x % per year to double is roughly equal to 70/x.

How long would it take for a population to double while increasing at 1% annually?

2%? 3%? 4%? 5%? 6%? 7%?

Crude Birth & Death RatesCrude Birth & Death Rates

How doe developed compare to developing countries?

Developed countries tend to have lower birth rates & death rates than developing countries (data from 1998).

Population ChangePopulation Change

The annual rate of population increase is generally expressed as a percentage.

What is the distribution pattern of growth rates in 1998?

Population SizePopulation Size

The world's ten most populous countries in 1998, with projections of population size in 2025.

Population SizePopulation Size

Population size by region in 1998, with projections of population size in 2025.

Population SizePopulation Size

United Nations projections of human population increase, based on fertilities ranging between 1.7 (low), 2.1 (medium), & 2.5 (high) children per woman.

Population SizePopulation Size

Average total fertility in 1998 was 2.9 children per woman.

What is considered the replacement rate?

The total size of the human population depends upon the year by which the replacement rate of 2.1 children per woman is reached.

Total Fertility in the United StatesTotal Fertility in the United StatesHow has the total fertility in the United States behaved?

We had a major increase during the "baby boom" (1946–64) & is now hovering just below replacement level.

Factors Affecting Fertility RatesFactors Affecting Fertility Rates• What are significant factors that decrease human fertility levels?• increase in average level of education & affluence;• decrease in importance of child labor;• increased urbanization;• increased cost of raising & educating children;• increased educational & employment opportunities for women;• decreased infant mortality;• higher average age of marriage;• greater availability of private & public pensions;• greater availability of reliable birth control;• greater availability of legal abortions;• change in religious beliefs, traditions, & cultural norms away from

encouraging large families.

U.S. Birth Control – Recommend?U.S. Birth Control – Recommend?

Death RatesDeath Rates

Infant death rates are lower in developed countries than developing countries.

How does this pattern differ from that of population change we saw before?

Birth & Death Rates Over TimeBirth & Death Rates Over Time• The rapid growth in the world's population has not

resulted from an increase in birth rates, but rather a major decrease in death rates.

• death rates have decreased markedly during the past 100 years;

• birth rates have also decreased, but not as fast as death rates;

• the increasing difference between birth & death rates is what has lead to exponential population growth;

• the patterns of change in birth & death rates over time are different for developed vs. developing countries.

Birth & Death Rates Over Time (1 of 2)Birth & Death Rates Over Time (1 of 2)

How are birth & death rates changing in developed countries?

In developed countries decreases in death rates are being accompanied by decreases in birth rates over time.

Birth & Death Rates Over Time (2 of 2)Birth & Death Rates Over Time (2 of 2)

How are birth & death rates changing in developing countries?

In developing countries decreases in death rates have not been accompanied by as large of decreases in birth rates over time, leading to major population increase.

2. Population Age Structure2. Population Age Structure

• What does a population age structure (population pyramid) show?

• Age structure refers to the proportion of the population in each age class:– prereproductive (0–14 years)– reproductive (15–44 years)– postreproductive (45 & up)

• Proportions of Males vs Females are also indicated on the left & right of each pyramid.

Population Age StructurePopulation Age Structure

How can you tell a population is rapidly or slowly growing?

Rapidly growing populations have pyramid–shaped age structures, with large numbers of prereproductive individuals.

Slower growing populations have a more even age distribution.

Population Age StructurePopulation Age StructureHow can you recognize zero

vs negative population growth?

Populations with zero population growth have nearly equal proportions of prereproductive & reproductive individuals.

Populations with negative growth have a greater proportion of reproductive than prereproductive individuals.

Population Age StructurePopulation Age StructureWhat does the diagram

indicate is expected to happen to developing countries?

Developing countries are expected to continue to have a pyramid shape through the year 2025, although the age structure will become somewhat more evenly distributed.

Population Age StructurePopulation Age StructureWhat does the

diagram indicate is expected of developed countries?

Populations of developed countries are expected to have an increasingly even age distribution through the year 2025.

Population Age StructurePopulation Age StructureWhat do the following age structures show about the U.S.?

Population age structure of the United States continues to show a bulge as the baby boom generation ages. This has been compared to watching a boa constrictor swallow a pig.

3. Solutions: Stabilizing Human Population3. Solutions: Stabilizing Human Population

• What did the projections of a model, published in The Limits to Growth In 1972?

• It indicated that if current economic, resource use, & population trends continue then we can expect economic & ecological collapse.

• What basic assumptions of industrial societies did this admittedly crude model challenge?

• That there are no limits to industrial & population growth. • What did there update twenty years later envision? • Beyond the Limits: Confronting Global Collapse, Envisioning a

Sustainable Future (Donella Meadows et al. 1992);• Despite limitations, computer models are an effective means for

exploring possible future scenarios.

Computer Models of Human PopulationComputer Models of Human Population

What does this computer model project might happen if the world's population & economy continue to grow exponentially at 1990 levels?

Computer Models of Human PopulationComputer Models of Human Population

What does this computer model project will happen if fertility is stabilized to 2 children per couple?

It shows that we can avoid overshoot & collapse to make a fairly smooth transition to a sustainable future.

Demographic Transition (1 of 5)Demographic Transition (1 of 5)What happens in the 4 stages of the demographic

transition?

Demographic Transition (2 of 5)Demographic Transition (2 of 5)

• What happens in the Preindustrial Stage:

• Both birth & death rates are relatively high & approximately equal, such that the population does not increase, & the population size is small.

Demographic Transition (3 of 5)Demographic Transition (3 of 5)

• What happens in the Transitional Stage?

• Death rate decreases markedly because of industrialization, increased food production, & improved health care; birth rates remain relatively high, such the population grows rapidly.

Demographic Transition (4 of 5)Demographic Transition (4 of 5)

• What happens the Industrial Stage?

• Birth rate drops & eventually approaches a balance with death rate, leading to a slowing of population growth.

Demographic Transition (5 of 5)Demographic Transition (5 of 5)

• What happens in the Postindustrial Stage?

• Birth rate & death rates approximately balance, zero population growth is attained, & the population stabilizes at a size much higher than the preindustrial size; if birth rate declines below death rate negative population growth may even be attained.

4. Case Studies – United States4. Case Studies – United States• Immigration in the United

States:• as fertility decreases,

immigration has become a major source of population increase in the U.S.;

• in 1998 the U.S. received about 935,000 legal immigrants & 400,00 illegal immigrants;

• working immigrants boost the economy in the long run;

• increasing levels of legal & illegal are expected.

Case Studies - IndiaCase Studies - India• Population Control in

India:• in 1952 India began the

first national family planning program;

• the program has been disappointing because of poor planning, inefficiency, low status of women, extreme poverty, & lack of funds;

• couples still have an average of 3.5 children because of the belief that they need children to work & care for them in old age.

Case Studies - ChinaCase Studies - China• Population Control in

China:• Since 1970, China,

with the world's largest population, has initiated efforts to better feed its people & control population growth;

• strict population control measures prevent couples from having more than one child;

• although considered coercive, the policy is significantly slowing population growth.

5. Human Population & Sustainability5. Human Population & Sustainability

• How can governments reduce population growth?• improve access to family planning & reproductive

health care;• improve heath care for infants, children, &

pregnant women;• encourage development of national population

policies;• improve equality between men & women;• increase access to education, especially for girls;• increase the involvement of men in child rearing

& family planning;• reduce poverty;• reduce & eliminate unsustainable patterns of

production & consumption.