Chapter 7

The Human Population

Scientists Disagree on Earth’s Carrying Capacity

Figure

7.1

Scientists Disagree on Earth’s Carrying Capacity

•The following graphs show theoretical models of food supply and population size.

•Could carrying capacity be changed?

•Whenever food supply seemed small enough to limit human population, major technological advances increased food production.

Factors that Drive Human Population Growth

•Demography- the study of human populations and population trends.

•Changes in Population Size

•Fertility

•Life Expectancy

•Age Structure

•Migration

Changes in Population Size

•Immigration- the movement of people into a country

•Emigration- the movement of people out of a country.

•Net migration rate- the difference between immigration and emigration in a give year per 1,000 people in the country.

Changes in Population Size

•Crude birth rate (CBR)= the number of births per 1,000 individuals per year.

•Crude death rate (CDR)= the number of deaths per 1,000 individuals per year.

• Global population growth rate = (CBR- CDR)/ 10

• National population growth rate = (CBR+ immigration) - (CDR + emigration)/ 10

• Doubling time (in years)- 70/growth rate

Fertility

•Total fertility rate- an estimate of the average number of children that each woman in a population will bear.

•Replacement level fertility- the total fertility rate required to offset the average number of deaths in a population and for the current population size to remain stable.

Fertility•Developed countries- countries with relatively

high levels of industrialization and income.•Typically see a replacement-level fertility of

2.1.•Developing countries- countries with relatively

low levels of industrialization and income of less that $3 per person per day.•Mortality among young people is higher and

TFR of greater than 2.1 is needed to achieve replacement-level fertility

Life Expectancy• Life expectancy- the average number of

years that an infant born in a particular year in a particular country can be expected to live, given the current average life span and death rate of that country.

Life Expectancy

•Availability of health care, access to good nutrition, and exposure to pollutants all factors in life expectancy

• Infant mortality rate- the number of deaths of children under 1 year of age per 1,000 live births.

•Child mortality rate- the number of deaths of children under age 5 per 1,000 live births.

Age Structure• Age structure diagrams - visual representations of age

structure within a country for males and females.• Each horizontal bar represents a 5-year age group.• The total area of all the bars in the diagram represents the size

of the whole population.• Population Pyramids – a type of age structure diagram that is

typical of developing countries, such as Venezuela and India.• The wide base of the graph indicate the population will grow

because a large number of females aged 0 to 15 have yet to bear children.

• If each of these potential mothers has only two children, the population will grow simply because there are increasing numbers of women able to give birth.

• Population Momentum – the reason a population keeps on growing after birth control policies or voluntary birth reductions have begun to lower the crude birth rate of a country.• The population pyramid illustrates that it takes time for

actions that attempt to reduce births to catch up with a growing population.

Country with little difference between individuals of

young and old age groups appear more like a column between ages 0 and 50. ex:

US, Canada, Australia, Sweden

Greater number of older people, resembles inverted

pyramid. TFR<2.1 Population will continue to shrink. Ex:

Italy, Germany, Russia

China – early stages of 7-8c graph.

Population Pyramid – widest at bottom. Indicates population will

grow in the future.

Migration• A country with relatively low CBR but a high immigration

rate may still experience population growth.• US has a TFR of 2.1 and an age structure diagram that is

approaching a column shape, but it has a high rate of immigration. As a result, the US population will probably increase by 44% by 2050.

• Net migration rate – the difference between immigration and emigration in a given year per 1,000 people in a country.• Positive net migration = more immigration than

emigration• Approximately 1 million people immigrate to the US

each year. Only a small number emigrate.• US population = 300 million = 3.3 immigrants/1,000

people• Negative net migration = more emigration than

immigration• Georgia (Western Asia) – growth rate of 0.2%, TFR =

1.4, net migration rate = -5/1,000 people.• Projected to have a 24% population decrease by 2050

The Demographic Transition

• The theory of the demographic transition is the theory that as a country moves from a subsistence economy to industrialization and increased affluence, it undergoes a predictable shift in population growth.

The Stages of the Demographic Transition

• Phase 1: Slow population growth because there are high birth rates and high death rates which offset each other. • Typical in countries before they modernize – Life expectancy for adults

relatively short due to difficult and dangerous working conditions. • Infant mortality rate high• US and Western Europe were in phase 1 before the Industrial Revolution

• Phase 2: Rapid population growth because birth rates remain high but death rates decline due to better sanitation, clean drinking water, increased access to food and goods, and access to health care.• India is in phase 2 today. US in phase 2 in the early 20th century.

• Phase 3: Stable population growth as the economy and educational system improves and people have fewer children.• Why do people produce fewer children as their income increases?

• As societies transition from subsistence farming to more complex economic specialization, having large numbers of children may become a financial burden rather than an economic benefit.

• Phase 4: Declining population growth because the relatively high level of affluence and economic develop encourage women to delay having children.• Japan, United Kingdom, Germany, Russia, and Italy are phase 4, with CBR well

below CDR.• Fewer people in labor force, more people retired or working part-time,

pension and social security services place greater tax burden on each wage earner, may be a shortage of health care workers for an aging country.

Family Planning

• Family planning- the regulation of the number or spacing of offspring through the use of birth control.• As the education levels of women increase and women earn

incomes of their own, fertility generally decreases.• When women have the option to use family planning, crude

birth rates tend to drop.• In Ethiopia, women with secondary school education or higher

have a TFR of 2.0, whereas the TFR among uneducated women is 6.1.

The 12 Most Populous Countries in the World

• 9 of the 12 most populous nations on Earth are developing countries.

• Although only 1/5 of the human population lives in developed countries, those people consume much more than ½ of the world’s energy and resources.

• Calculating per capita ecological footprint for a country provides a way to measure the effect of affluence – money, goods, or property, on the planet.• World average = 2.7 ha (6.7 acres) • US (largest footprint) = 9.0 ha (22

acres)• China = 1.8 ha (4.5 acres)• Haiti = 0.5 ha (1.2 acres)

• With China’s rapid development, it’s ecological footprint is likely to exceed that of the US within the next 10 years.

The relationship between economic development and population growth rate for developing nations.

Ecological Footprints

•Affluence - having a lot of wealth such as money, goods, or property.

The IPAT Equation

•To estimate the impact of human lifestyles on Earth we can use the IPAT equation:

•Impact= Population X Affluence X Technology

• Urban area – according to the US Census Bureau, is one that contains more than 386 people per square kilometer (1,000 people per square mile).• New York is the most

densely populated city in the US, with 10,400 people per square km (27,000 people per square mile).• Mumbai, India is the most

densely populated city in the world, with 23,000 people per square km (60,000 people per square mile).

• More than 75% of people in developed countries live in urban areas.

The Impact of Affluence

•Gross domestic product (GDP)- the value of all products and services produced in a year in that country.

•GDP is made up of consumer spending, investments, government spending, and exports minus imports.

•A countries GDP often correlates with its pollution levels.