Human Population Dynamics (College Board AP® Environmental Science): Study Guide

Human population growth & decline

Factors influencing human population growth and decline

Birth rates

• High birth rates are a major driver of population growth

  • Example: In developing countries, high birth rates are often linked to limited access to family planning and education

  • Lower birth rates are associated with developed nations where access to contraception, education, and career opportunities is more widespread

Infant mortality rates and overall death rates

• High infant mortality rates (IMR) often lead to higher birth rates as families compensate for potential child loss

  • Example: In regions with limited healthcare access, such as parts of Sub-Saharan Africa, high IMR contributes to population growth

• Declines in IMR, driven by improved healthcare and nutrition, can stabilize or reduce birth rates over time

• Overall death rates also influence population trends:

  • Declining death rates due to advancements in medicine and sanitation increase population growth

  • Conversely, high death rates from disease or conflict can lead to population decline

Access to family planning

• Family planning services provide contraception and reproductive health education

  • Access to these services reduces unintended pregnancies, leading to lower birth rates and slower population growth

  • Example: Thailand’s family planning programs have successfully reduced birth rates over the past decades

Access to good nutrition

• Adequate nutrition reduces mortality rates and improves health outcomes

  • Populations with access to nutritious food tend to have lower birth rates, as infant and child survival is more assured

Access to education

• Education, particularly for women, significantly impacts population growth:

  • Educated women marry later, have fewer children, and are more likely to use family planning services

Postponement of marriage

• Delaying marriage reduces the period of time during which many women are likely to have children

  • Societies where women marry later often exhibit lower fertility rates and slower population growth

Factors limiting global human population

Carrying capacity of Earth

• Carrying capacity refers to the maximum number of individuals that an environment can sustain indefinitely

  • Human populations rely on finite resources such as food, water, and energy

  • When populations exceed carrying capacity, environmental degradation and resource depletion occur

  • Example: Overextraction of groundwater in regions like India has led to water shortages and declining agricultural yields

• Factors influencing carrying capacity include:

  • Availability of resources: Food, water, and shelter are critical for sustaining human populations

  • Technological advancements: Innovations in agriculture and energy production can temporarily increase carrying capacity

  • Environmental constraints: Climate change, deforestation, and pollution can reduce the Earth’s capacity to support human populations

Malthusian theory

• Proposed by Thomas Malthus

• This theory suggests that human population growth tends to outpace the growth of food production

  • Key idea: Population grows exponentially, while food supply shows linear growth, leading to inevitable resource shortages

• Malthusian checks are natural limits on population growth

• They include:

  • Positive checks: Events that increase mortality rates, such as famine, disease, and war

  • Preventive checks: Measures that lower birth rates, such as family planning and delayed marriage

• Critiques and adaptations of Malthusian theory:

  • Critics argue that technological advancements have allowed food production to keep pace with population growth

  • More recent perspectives include modern challenges like climate change and water scarcity as new limiting factors

Density-dependent & density-independent factors

Density-dependent factors

• Definition:

  • Density-dependent factors are influenced by the size and density of the population

  • This means their effects become more pronounced as populations grow

• Examples of density-dependent factors:

  • Access to clean water and air:

    • Larger populations face increased pollution and strain on water supplies

    • Example: Urban areas with high population density may experience water shortages or water and air pollution due to industrial emissions

  • Food availability:

    • Competition for food intensifies as population density increases

    • This eventually leads to food scarcity

    • Example: Overpopulation in regions with limited agricultural capacity can cause famine

  • Disease transmission:

    • Crowded conditions facilitate the spread of infectious diseases

    • Example: High-density urban areas have a greater risk of disease outbreaks, such as during the COVID-19 pandemic

  • Territory size:

    • As populations grow, competition for space increases, leading to conflicts and overcrowding

    • Example: Overcrowding in slums often results in poor living conditions and health issues

Density-independent factors

• Definition:

  • Density-independent factors affect populations regardless of their size or density

• Examples of density-independent factors:

  • Major storms:

    • Severe weather events can cause widespread destruction and loss of life

  • Fires:

    • Wildfires destroy homes, ecosystems, and infrastructure, impacting human populations

  • Heat waves:

    • Prolonged periods of extreme heat can lead to health crises and increased mortality

  • Droughts:

    • Extended dry periods reduce water availability and agricultural productivity

The rule of 70

What is the rule of 70?

• The rule of 70 is a simple formula used to estimate the time it takes for a population to double in size based on its annual growth rate

• Formula:

  • Doubling time (years) = 70 / percentage population growth rate

• Example:

  • A population with a growth rate of 2% will double in approximately 70 / 2 = 35 years

Applications of the rule of 70

• Helps predict future population size and resource needs

• Useful for comparing growth rates across different countries or regions

  • Example: a country with a high growth rate (e.g., 3%) will double its population much faster than one with a low growth rate (e.g., 0.5%)

• Highlights the impacts and pressures of rapid population growth on resources and infrastructure

Limitations of the rule of 70

• Assumes constant growth rates, which may not reflect real-world scenarios

• Does not account for factors like migration, changes in fertility rates, or sudden environmental impacts