Population, Consumption, and Resource Use

Population Basics

• Population: Defined as a group of individuals of a single species living in the same geographic area.
• Population Density: The number of individuals per unit area or volume.
  • Additions: Births and immigration (individuals entering the population). Higher birth rates increase population size.
  • Subtractions: Deaths and emigration (individuals leaving the population). Higher death rates decrease population size.
• Demography: The study of the vital statistics of a population and how they change over time.
• Life Table: An age-specific summary of the survival pattern of a population. It is best constructed by following the fate of a cohort.
• Cohort: A group of individuals all born in the same year.
• Life Expectancy: The length of time individuals remain in the population; influenced by resource availability, reproduction rates, and health.
• Infant Mortality: Varies widely among developed and developing countries; does not capture the full range of the human condition.
• Survivorship Curve: A graphic way of representing data in a life table. There are three primary types:
  • Type I: High juvenile survival; most mortality occurs among older individuals. Example: Humans.
  • Type II: Individuals die at equal rates regardless of age. Example: Birds.
  • Type III: Individuals die at a high rate as juveniles, with much lower mortality rates later in life. Example: Trees.

Reproductive Rate and Fertility

• Reproductive Rate: The growth rate of a population per generation.
• $R_0$: Equivalent to the net reproductive rate, or the total number of female offspring each female produces over her lifetime.
• Reproductive Table / Fertility Schedule: An age-specific summary of reproductive rates in a population.
• Fertility Rate: The number of children women have, or are expected to have, during their reproductive years.
• Total Fertility Rate (TFR): The average number of children born per woman. A value below $2.1$ will cause the native population to decline over time.
• Key Facts and Trends in Fertility (Focus on the Philippines):
  • According to the 2018 United Nations Population Fund (UNFPA), the Philippines had the highest fertility rate in the Association of Southeast Asian Nations (ASEAN) region at $2.9$, along with the 2nd largest population in ASEAN at $106.5\text{ million}$.
  • Historical and projected fertility rate trajectory in the Philippines: $4.1$ (in 1993) $\rightarrow$ $1.9$ (in 2022) $\rightarrow$ $1.7$ (projected for 2025), reflecting a shift described as "from baby boom to bust".
  • A 2023 Philippine Institute for Development Studies (PIDS) study attributed the reduced fertility rate to:
    • Improved socioeconomic status ($25.7\%$)
    • Changes in marriage patterns ($14.6\%$)
    • Family planning use ($14.6\%$)
    • Decrease in the desired number of children ($6.7\%$)
    • Improved child survival ($5.6\%$)

Life History Traits

• Life History: The series of changes undergone by an organism during its lifetime. It encompasses traits such as age at maturity, reproductive patterns, number of offspring, size of offspring, and lifespan.
• Semelparity: Known as "big-bang reproduction"—an strategy where an organism reproduces a single time and then dies.
• Iteroparity: Known as "repeated reproduction"—a strategy where an organism produces offspring repeatedly over time.

Models of Population Growth

• Exponential Growth Model:
  • Describes population growth in an idealized, unlimited environment where resources are abundant.
  • Produces a J-shaped growth curve.
  • Characteristic of populations that are rebounding from a drastic crash or entering a new, unexploited habitat.
• Logistic Growth Model:
  • A more realistic growth model that limits population growth by incorporating environmental limits.
  • Produces an S-shaped growth curve.
  • Carrying Capacity ($K$): Defined as the maximum population size that a particular environment can sustain over time given its available resources.

K-Selection vs. r-Selection

• $K$-selection:
  • Also called Density-dependent selection.
  • Selects for life history traits that are sensitive to population density; birth rates fall and death rates rise as population density increases near carrying capacity ($K$).
  • Examples:
    • Chimpanzee (produces $1$ offspring every $5\text{ years}$)
    • Large Cat / Puma (produces $2$ offspring a year)
    • Hare (produces $12$ offspring a year)
• $r$-selection:
  • Also called Density-independent selection.
  • Selects for life history traits that maximize reproductive success ($r$) in uncrowded environments; birth and death rates do not change with population density.
  • Examples:
    • Oyster (produces $500\text{ million}$ offspring a year)
    • Fish / Tuna (produces $6,000$ offspring a year)
    • Frog (produces $200$ offspring a year)

Human Population Dynamics

• Global Population Growth:
  • Current world population is approximately $8.3\text{ billion}$ ($8,317,747,887$ as of September 2026).
  • Human population grew relatively slowly until about the year 1650, after which it began growing exponentially.
  • Global growth has slowed in recent decades after centuries of exponential increase.
  • Projections estimate the global population will reach $10\text{ billion}$ by 2060 and $10.2\text{ billion}$ by 2100.
• Demographic Statistics by Nation:
  • Top 3 most populous countries: India ($1.479\text{ billion}$), China ($1.412\text{ billion}$), United States ($349\text{ million}$).
  • Philippines population: Approximately $117.9\text{ million}$, ranking 13th to 14th globally.
• Impact on Wildlife:
  • Global wildlife populations plummeted significantly between 1970 and 2016.
  • Humans make up a tiny fraction of total terrestrial vertebrate land animal biomass compared to domesticated livestock.

Demographic Transition Model

• Demographic Transition: A theoretical model describing the changing patterns of mortality, fertility, and growth rates as societies transition through economic and industrial development.
• Five Stages of Demographic Transition:
  • Stage I (Pre-Industrial): High birth rates and high death rates; total population size remains relatively low and highly fluctuating.
  • Stage II (Industrial Revolution / Early Expanding): Death rates fall rapidly due to improved sanitation and food supply while birth rates remain high; results in very rapid population growth.
  • Stage III (Post-Industrial Revolution / Late Expanding): Birth rates begin to decline while death rates remain low; population increase begins to slow down.
  • Stage IV (Stabilization / Low Stationary): Low birth rates and low death rates; population stabilizes with very slow increase.
  • Stage V (Declining Population): Birth rates drop below death rates (TFR below $2.1$); total population size decreases.

Age Structure and Population Pyramids

• Age Structure: The relative number of individuals at each age level within a population; commonly visualized using age-structure pyramids.
• Population Pyramid: A graphical illustration showing the distribution of various age groups as well as the sex distribution in a population.
• Three Main Pyramid Shapes:
  • Wide Base (Expansive):
    • Indicates rapid population growth.
    • Characterized by a high percentage of young people.
    • Example: Afghanistan.
  • Narrow Base (Constrictive):
    • Indicates slow or declining population growth.
    • Characterized by a lower percentage of younger people and declining birth rates.
    • Example: United States (slow growth).
  • Equal Proportion (Stationary):
    • Indicates a non-growing, stable population.
    • Characterized by roughly equal proportions of individuals across all age groups up to older ages.
    • Example: Italy (population decrease/zero-growth profile).

Population Growth and Resource Use

• Resource Pressures by 2050:
  • Global human population is projected to increase by $2.5\text{ billion}$ people by 2050.
  • Global demand for food is projected to rise by $60\%$
  • Global fresh water supply is projected to fall $40\%$ short of current levels by 2050.
• Interactions of Population and Consumption:
  • Resource demand is determined both by absolute population size and per-capita consumption rates.
  • Neither population size nor consumption habits alone account for total environmental degradation; they interact continuously.
• Comparison of Consumption Lifestyles:
  • Diet: Plant-based diets require lower resource consumption; high demand for animal products requires higher resource consumption.
  • Transport: Walking, cycling, and public transit result in lower resource consumption; high private-vehicle use and frequent air travel require higher resource consumption.
  • Housing: Smaller, energy-efficient housing requires lower resource consumption; larger homes with high energy demand require higher resource consumption.
  • Products: Durable, repairable goods require lower resource consumption; frequent product replacement and high material turnover require higher resource consumption.
  • Energy: Renewable and energy-efficient systems require lower resource consumption; energy-intensive fossil fuels require higher resource consumption.
  • Waste: Reuse, repair, and recycling minimize resource demand; high single-use material consumption leads to high environmental impact.
• Resource Supply Chains (Consumption Chains):
  • Forest Chain: Forest $\rightarrow$ timber extraction $\rightarrow$ furniture production $\rightarrow$ household use $\rightarrow$ discarded materials.
  • Soil/Water Chain: Soil and water $\rightarrow$ agricultural crops $\rightarrow$ industrial food processing $\rightarrow$ consumption $\rightarrow$ organic waste.
  • Fossil Fuel Chain: Fossil fuels $\rightarrow$ electricity generation $\rightarrow$ household appliances $\rightarrow$ consumer services $\rightarrow$ greenhouse gas emissions.

Resource Classification and Depletion

• Renewable Resources: Resources that can replenish through natural biological or physical processes, provided their rate of extraction does not exceed their rate of natural renewal.
  • Examples: Forests, freshwater, fisheries, soil biomass, solar energy.
  • Critical Rule: Renewable resources are not unlimited; their renewability depends strictly on active ecological management and recovery times.
• Nonrenewable Resources: Resources that form over geological time scales so slowly that they are effectively finite on human time scales.
  • Examples: Coal, petroleum, natural gas, mineral ores.
• Resource Depletion: The exhaustion or decline of resource stocks and productive capacity due to human activity.
• Five Major Causes of Resource Depletion:
  1. Overextraction: Harvesting biological or physical materials faster than their natural rate of replenishment.
  2. Land Conversion: Replacing native ecosystems with agricultural fields, highways, and urban infrastructure.
  3. Pollution: Degrading the quality and functional usability of air, freshwater, and soil resources.
  4. Climate Change: Disrupting natural precipitation cycles, agricultural productivity, and ecosystem resilience.
  5. Habitat Degradation: Fragmenting natural ecosystems and destroying essential biodiversity functions.

Environmental Inequality

• Environmental Inequality: The disproportionate or unequal distribution of environmental harms, risks, resource consumption, and environmental benefits among different social groups, regions, or communities.
• Mechanisms of Environmental Inequality:
  • High-income populations consume a disproportionately large share of energy, land, and material resources.
  • Low-income communities rely directly on local natural resources for daily survival and lack adaptive buffers.
  • Polluting industries, hazardous waste facilities, and landfills are disproportionately sited near vulnerable or marginalized communities.
  • Marginalized populations often lack access to clean water, adequate sanitation, energy infrastructure, and healthy environments.
  • Communities that contribute the least to global environmental degradation often bear the most severe consequences.
• Case Example (Philippines):
  • Encroachment on Aeta ancestral land in Zambales, where local government units (such as the Subic LGU) faced severe criticism for establishing garbage dumps on indigenous ancestral property.

Resource Use Pressure and Ecological Impacts

• Deforestation: Causes habitat loss, biodiversity decline, and increased carbon emissions.
• Intensive Agriculture: Causes soil degradation, loss of soil nutrients, and aquatic water pollution.
• Fossil Fuel Use: Causes outdoor and indoor air pollution and greenhouse gas emissions.
• Mining Operations: Causes landscape alteration, massive solid waste generation, and chemical contamination.
• Excessive Water Extraction: Reduces natural streamflow, leads to wetland degradation, and causes severe groundwater depletion.
• High Material Consumption: Drives increased raw material extraction, excessive waste generation, and elevated global energy demand.
• Spatial Disconnect: Environmental impacts frequently occur far from the geographic location where finished goods are ultimately consumed.

Global Carrying Capacity and Ecological Footprint

• Global Carrying Capacity: The absolute limit of Earth's biological systems to sustain human life remains uncertain and subject to ongoing debate.
• Ecological Footprint:
  • Definition: Summarizes the aggregate land and water area required to sustain a person or nation by producing all consumed resources and absorbing all generated wastes.
  • Unit: Measured in global hectares ($\text{gha}$).
  • Purpose: Serves as a quantitative metric to measure how close human demand is to the biological carrying capacity of Earth.
• Ecological Overshoot and Deficit:
  • Humanity has been in a state of ecological overshoot since the mid-1980s.
  • Human consumption currently exceeds Earth's biological regeneration capacity: it takes Earth approximately $1\text{ year and }6\text{ months}$ to regenerate the biological resources that humanity uses in a single year.
  • With a global human population surpassing $8\text{ billion}$, the world operates in a permanent ecological deficit.
• Geographic Disparities in Ecological Footprint and Biocapacity:
  • Countries with the Largest Total Footprint: China, United States, India, Russia, Japan.
  • Countries with the Smallest Total Footprint: Burundi, Haiti, Afghanistan.
  • Countries with the Highest Ecological Deficit: United Arab Emirates (UAE), Qatar.
  • Countries with the Highest Biocapacity Reserves: Brazil, Canada, Finland, Australia.
• Earth Overshoot Day: The specific calendar date on which humanity's resource consumption for the year exceeds Earth's capacity to regenerate those biological resources in that same year.

The IPAT Framework

• Formula:     \n    I = P \times A \times T\n    
• Variable Definitions and Components:
  • $I$ (Environmental Impact): Total environmental degradation, including carbon emissions, resource depletion, and land transformation.
  • $P$ (Population): Total number of human individuals in a given area or globally.
  • $A$ (Affluence): Level of consumption or resource use per individual person.
  • $T$ (Technology): Environmental impact caused per unit of resource consumed, determined by technical efficiency.
• Mathematical Behavior of Variables:
  • An increase in Population ($P \uparrow$) leads to an increase in Impact ($I \uparrow$).
  • An increase in Affluence ($A \uparrow$) leads to an increase in Impact ($I \uparrow$).
  • A reduction/improvement in Technological impact ($T \downarrow$) leads to a decrease in overall Impact ($I \downarrow$).
• Numerical Calculation Example:
  • Baseline Scenario: $I = 1,000 \times 2 \times 3 = 6,000$
  • Scenario with Population Increase: If population increases from $1,000$ to $1,200$, then $I = 1,200 \times 2 \times 3 = 7,200$
• Application of IPAT to Sustainable Resource Strategies:
  • Addressing $P$:
    • Strategies: Increasing access to education, expanding healthcare, promoting gender equality, and providing voluntary family planning.
    • Intended Effect: Supports informed reproductive choices and stabilizes population growth rates.
  • Addressing $A$:
    • Strategies: Reducing waste, encouraging responsible consumption, favoring durable products, and adopting energy-efficient lifestyles.
    • Intended Effect: Lowers individual resource consumption per person.
  • Addressing $T$:
    • Strategies: Transitioning to renewable energy, developing energy-efficient mass transit, practicing sustainable agriculture, and implementing cleaner manufacturing technologies.
    • Intended Effect: Lowers the environmental impact per unit of consumption produced.
• Urban Transportation Example Analysis:
  • $P$ Factor: As urban populations expand, the total count of commuters needing transport increases.
  • $A$ Factor: As average urban income increases, per-capita vehicle ownership rises (e.g., purchasing private cars or motorcycles), increasing per-capita fuel consumption.
  • $T$ Factor: If transportation relies on conventional internal combustion engines, environmental impact per mile is high; if the city transitions to electric mass transit powered by clean grids, environmental impact per trip drops dramatically.
  • System Outcome: High population ($P$) + High individual travel consumption ($A$) + High-emission fossil technology ($T$) = Massive environmental degradation ($I$). Conversely, technological advances ($T \downarrow$) combined with sustainable urban planning can offset growth in population and affluence.