Chapter 7

The Human Population

Crowded Street in China

Oh, the humanity• In 1830 the world

reached the one billion mark.

• By 1930 we were at two billion.

• 1960, a mere 3 billion.• 1975, four billion.• In 1996 we passed 6

billion.• We will pass 7 billion by

2013

China: 1.3 billion peopleChina: 1.3 billion people =1/5 of world’s population =1/5 of world’s population

• since 1970 efforts to better feed 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.

India: 1 billionIndia: 1 billion=1/5 of world’s population=1/5 of world’s population

• 1952 first national family planning program;

• program disappointing;

• fertility still 3.5.

Patterns of growth• Until the 1800s disease

slowed population growth.• The human population was

in balance with nature.• Breakthroughs – Discovery

by Louis Pasteur that diseases were caused by infectious agents.

• Free from natural enemies the human population began to grow exponentially.

Population Growth

• Populations show two types of growth– Exponential

• J-shaped curve• Unlimited Growth• Growth is independent of population density

– Logistic • S-shaped curve• Growth affected by environmental stress• Growth is not independent of population density

Exponential and Logistic Population Growth: J-Curves and S-Curves

• Populations grow rapidly with ample resources, but as resources become limited, its growth rate slows and levels off.

Figure 8-4Figure 8-4

Rule of 70

• To determine the doubling time of a population, divide 70 by the percentage of growth.– Uses the exponential growth calculation– If the growth rate is 2%, then,– 70 ÷ 2 = 35 years

Population Explodes after the Industrial Revolution

Resource Consumption (6)

• High consumption

• Getting worse• Rate increase

faster than population growth

Resource Limits - Land (7)

• Deforesting to acquire more arable land

• Would run out in next century at current yields

• Probably need to double yields

Energy Consumption (9)

• Energy growth very high last fifty years

• Mostly hydrocarbon fuels

• Nonrenewable resource consumption and climate change issues

Billions

Less Developed Regions

More Developed Regions

Source: United Nations, World Population Prospects: The 2004 Revision (medium scenario), 2005.

Growth in More, Less Developed Countries

Population growth for rich and for poor

• 98% of the world population growth is occurring in developing countries.

Scientists Disagree on Earth’s Carrying Capacity

Figure

7.1

Fertility & Mortality: in 2002:US crude birthrate = 15/1000,

crude death rate = 9/1000,

natural growth rate = 6/1000 or 0.6%

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

Just the facts, mam

• A total fertility rate of 2.0 will give a stable population. That’s two children per woman.

• Greater than 2 will give rise to a growing population.

• The fertility rate in developing nations is 2.9.

Birthrate and death rate

• Crude Birth rate and crude death rate are the number of births and deaths per thousand of a population each year.

Population Change• Population Change = (Births +Immigration) – (Deaths + Emigration)

• Zero Population Growth (ZPG) – When the population size remains stable.

• Birth Rate – The number of live births per 1,000 people in a population in a given year.

• Death Rate – The number of deaths per 1,000 people in a population in a given year.

• birth rate and death rate reported as the number per thousand people;

• zero population growth (ZPG) occurs when births balance deaths

Population Size (N)Population Size (N)

Population ChangeBirths

+Immigration

Deaths+

Emigration–=

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• 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.

Population projections by regions (1999 – 2025)

Over 95% of this increasewill take place in “DevelopingCountries”

Human population growth: 7 billion• Populations continue to rise in most countries

– Particularly in poverty-stricken developing nations• Although the rate of growth is slowing, we are still

increasing in absolute numbers

It would take 30 years, counting once each second, to count to a billion!

Fertility• Population growth occurs

when births outnumber deaths.

• 2.0 is a stable rate for a population.

• This is replacement level fertility.

• It has declined in developed countries to 1.5.

• In developing countries it has increased to over 3.0 and some are as high as 5.

The human population is still growing rapidly

• It took all of human history to reach 1 billion• In 1930, 130 years later, we reached 2 billion,

and added the most recent billion in 12 years

Due to exponential growth, even if the growth rate remains steady, population will continue to grow

Factors That Affect Birth and Fertility Rates

• 1. Average level of education – In developing countries, women with no education generally have two more children than women with a secondary education

Factors That Affect Birth and Fertility Rates continued…

• 2. Importance of children as a part of the labor force – Rates tend to be higher in developing countries where children begin working at an early age.

• 3. Urbanization – People in urban areas usually have easier access to family-planning services. Rural families tend to need more children to work and don’t have practical access to family-planning services.

• 4. Cost of raising and educating children – Raising children is much more costly because children don’t enter the labor force until their 20’s.

Factors That Affect Birth and Fertility Rates part 3…

• 5. Educational and employment opportunities for women – Rates tend to be lower when women have access to education and paid employment outside the home.

• 6. Infant mortality rate – In areas with low infant mortality rates, people tend to have fewer children when their average age at marriage is 25 years or older

• 7. Availability of private and public pension systems – Pensions eliminate the need of parents to have many children to help support them in old age.

Factors That Affect Birth and Fertility Rates part 4…

• 9. Religious beliefs, traditions, and cultural norms – In some countries, these factors favor large families and strongly oppose some forms of birth control.

• 10. Availability of reliable methods of birth control

Link Link

Population growth affects the environment

• The IPAT model: I = P x A x T x S– Our total impact (I) on the environment results from the

interaction of population (P), affluence (A) and technology (T), with an added sensitivity (S) factor

– Population = individuals need space and resources– Affluence = greater per capita resource use– Technology = increased exploitation of resources– Sensitivity = how sensitive an area is to human pressure– Further model refinements include education, laws,

ethics

Humanity uses 1/3 of all the Earth’s net primary production

A changing age structure poses challenges

• Many populations are getting older– Older people need care and financial assistance– But, also reduces the number of dependent

children and crime rates

POPULATION AGE STRUCTURE

• The number of people in young, middle, and older age groups determines how fast populations grow or decline.

• The number of people younger than age 15 is the major factor determining a country’s population growth.

• Changes in the distribution of a country’s age groups have long-lasting economic and social impacts.

Population profile of the United States

• A population profile is a bar graph showing the number of proportion of people at each age for a given population.

• The field of collecting information about population is called demography.

• Take a look at the bar graphs on page 131.

Population growth depends on various factors

• Whether a population grows, shrinks, or remains stable depends on:– Rates of birth, death, and migration– Birth and immigration add individuals– Death and emigration remove individuals

• Technological advances led to dramatic decline in human death rates – Widening the gap between birth rates and

death rates resulting in population expansion

Immigration and emigration play large roles

• Refugees flee their home country as a result of war, civil strife, and environmental degradation– 25 million escape poor environmental conditions– Movement causes environmental problems with no

incentives to conserve resources

Calculating Fertility Rates and Doubling Times

(CBR - CDR)/1000 x 100 = % Rate of Increase or decrease in population per 1000 per year

70/ Rate of Increase = Doubling Time

Population pyramids are used to show information about the age and gender of people in a specific country.

Male Female

Population in millions

In this country

there is a high Birth

Rate

There is also a high

Death Rate.

This population pyramid is typical of countries in poorer parts of the

world (LEDCs.)

Population characteristics

Age structure affects future population size

• Having many individuals in young age groups results in high reproduction and rapid population growth

Age pyramid of the U.S. in 2005

Computer simulations predict the future

• Simulations project trends in population, food, pollution, and resource availability

• If the world does not change, population and production will suddenly decrease

• In a sustainable world, population levels off, production and resources stabilize, and pollution declines

Demography• All population principles apply to humans

– Environmental factors limit population growth• Humans can raise the environment’s carrying capacity

through technology– How many humans can the world sustain? 1 – 33 billion

– Population growth can’t continue forever

Demography• Demography = the

application of population ecology to the study of humans– Demographers study

population size, – Density and distribution,– Age structure, sex ratio, – And birth, death,

immigration, and emigration rates

Population size and density• Nobody knows the

ultimate human population size

• But numbers are not the only important aspect

• Highest population density is in temperate, subtropical, and tropical biomes– Some areas are heavily

impacted by urbanization, pollution, and fossil fuel use

Infant Mortality RatesInfant Mortality Rates

Life expectancy is increasing

• Natural rate of population change = due to birth and death rates alone– In countries with good sanitation, health care,

and food, people live longer• Life expectancy = average number of years

that an individual is likely to continue to live– Increased due to reduced rates of infant

mortality– Urbanization, industrialization, and personal

wealth

The Poverty Cycle

The demographic transition

• Demographic transition = a model of economic and cultural change to explain the declining death and birth rates in industrializing nations

• Stable preindustrial state of high birth and death rates change to a stable post-industrial state of low birth and death rates

• As mortality decreases, there is less need for large families– Parents invest in quality of life

The demographic transition’s four stages

Population growth is seen as a temporary phenomenon

Phases of demographic transition• Phase 1 – high births offset

by high deaths. Slow• Phase 2 Epidemiologic

transition takes place. Fast!• Phase 3 Stable.• Phase 4 Low birth and

death rates and stability is achieved. Decline.

• Developed are in phase 4.• Developing are in two and

three.

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.

• 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.

• Phase 3: Stable population growth as the economy and educational system improves and people have fewer children.

• Phase 4: Declining population growth because the relatively high level of affluence and economic develop encourage women to delay having children.

Empowering women reduces growth rates

• Fertility rates drop when women gain access to contraceptives, family planning programs and better educational opportunities

• In 2007, 54% of married women worldwide used contraception; – China = 86%; the U.S. = 68%; 20 African nations < 10%

Women with little power have unintended pregnancies

Family planning reduces unintended pregnancies

Blue = family planning accessibleRed = family planning not accessible

Gender equity• Women lack the information and personal

freedom to achieve equal power with men– 2/3 of people who cannot read, and 60% of those

living in poverty are women

We are still a long way from achieving gender equality

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.

Poverty and population growth are correlated

• Poorer societies have higher growth rates than wealthier societies– Consistent with the demographic transition theory– They have higher fertility and growth rates, with lower

contraceptive use

99% of the next billion people added will be born in poor, less developed regions that are least able to support them

Poverty results in environmental degradation

Africa’s Sahel region and western China is turning to desert

The dark side of affluence• The average American eats

three times the global average for meat.

• We consume 75 pounds of paper per person.

• Because we are the biggest consumers we are also one of the biggest polluters.

• We have 5% of the world’s population and generate 24% of global carbon emissions.

• The world’s wealthiest 20% consumes 80%.

The Earth can’t support our consuming lifestyle

Humanity’s global ecological footprint surpassed Earth’s capacity to support us in 1987

Human Carrying CapacityHuman Carrying Capacity

Can the world/biosphere provide an adequate standard for the increasing population or are we at the limit?

Effects of Overpopulation?

• Food Shortage - famine

• Natural resources shortage

• Land Overuse• War• Disease• Pollution-waste

management

5 Important Trends

1. The proportion of people living in urban areas is increasing.– From 1850 to 2006 the rate of growth has grown

from 2% to 47.5%

2. The number of large urban areas is growing. – Megacities or megalopolises

Trends, continued

3. Urban population is increasing rapidly in developing countries.– This trend is leading to centers of poverty.

4. Urban growth is slower in developed countries.– Why do you think that is?

5. Poverty is becoming an urban trend as opposed to a rural one.

Urban Sprawl• When land is available and affordable, urban

areas tend to sprawl outward because:– Federal government loan guarantees stimulated the

development of suburbs.– Low-cost gasoline and government funding of

highways encourages automobile use.– Tax-laws encourage home ownership.– Most zoning laws separate residential and

commercial use of land.– Many urban areas lack proper planning.

More problems with sprawl

• Land Use– more land is being converted from agricultural to

residential, residential land is being proportioned at a high per capita rate

• Economics– tax money is spent on new developments and

upgrading existing services to meet the demand (where have we seen this?)

Fig. 23-6, p. 553

Natural Capital Degradation

Urban Sprawl

Land and Land and BiodiversityBiodiversity

Human Health and Human Health and AestheticsAesthetics

WaterWater Energy, Air, Energy, Air, and Climateand Climate

Economic EffectsEconomic Effects

Loss of cropland Contaminated drinking water and air

Increased runoff

Increased energy use & waste

Higher taxes

Loss of forests and grasslands

Increased surface water & groundwater pollution

Decline of downtown business districts

Increased air pollution

Weight gainLoss of wetlandsIncreased greenhouse gas emissions

Noise pollution

Increased use of surface water and groundwater

Increased unemployment in central city

Loss and fragmentation of wildlife habitats

Sky illumination at night

Enhanced global warming

Decreased storage of surface water and groundwater

Loss of tax base in central city

Increased wildlife roadkill

Traffic congestion

Warmer microclimate (urban heat island effect)

Increased soil erosion

Increased flooding

Decreased natural sewage treatment

URBAN RESOURCE AND ENVIRONMENTAL PROBLEMS

• Urban areas rarely are sustainable systems.Figure 23-8Figure 23-8

Microclimates

• A microclimate is the climate of a small area that is different from the area around it. It may be warmer or colder, wetter or drier, or more or less prone to frosts.

• Microclimates may be quite small - a protected courtyard next to a building, for example, that is warmer than an exposed field nearby. Or a microclimate may be extensive - a band extending several miles inland from a large body of water that moderates temperatures.

Consequences of Exploding Populations

More PopulationCauses

MORE

LESS

deforestationresource depletionloss of agricultural landbiodiversitydiseasepest resistancepopulation migrationirrigationwetlands