Lesson 2: Human Population Growth Big Question Why Is Human Population Growth the Underlying Environmental Problem?

Lesson 2 / ESRM100 / University of Washington The Prophecy of Malthus “the power of population growth” is “greater than the power of Earth to produce subsistence.”

Lesson 2 / ESRM100 / University of Washington Basic Concepts of Population Dynamics A population is a group of individuals of the same species living in the same area or interbreeding. A species is all individuals that are capable of interbreeding and is made up of populations. Abundance is the size of a population. The birth rate is the number of individuals born during a specified time interval. The death rate is the number of individuals who die during that same time interval. The growth rate is the difference between birth rate and death rate; the net change in the size of the population.

Lesson 2 / ESRM100 / University of Washington Exponential Growth Growth is exponential when it occurs at a constant rate per time period Produces a J-shaped growth curve The human population has mostly grown exponentially

Lesson 2 / ESRM100 / University of Washington Major Periods of Human History The early period of hunters and gatherers - less than a few million people The rise of agriculture - first major increase in the human population The Industrial Revolution - improvements in the food supply and health care led to a rapid population growth Today -growth has slowed in industrialized nations but is increasing rapidly in many less developed nations

Lesson 2 / ESRM100 / University of Washington The Logistic Growth Curve Exponential population growth cannot go on forever; people would eventually run out of food and space. The birth rate should decline and the death rate should rise, so that the growth rate slows to zero. The population should follow a smooth S-shaped curve. The population increases exponentially when small, so the curve rises steeply. Then the rate of growth gradually declines, until it reaches an upper population limit - the logistic carrying capacity.

Lesson 2 / ESRM100 / University of Washington Is the Logistic Growth Curve Realistic? Requires accurate knowledge of the inflection point where growth rate declines. Unrealistic assumptions for human populations. Death rates do not increase if there are ongoing improvements in health care and food supplies. See the estimated US population at Population Clocks: Clocks

Lesson 2 / ESRM100 / University of Washington Other Clues to Population Change Age structure - the proportion of the population in each age group. Four general types: Pyramid Column Inverted pyramid Column with bulge

Lesson 2 / ESRM100 / University of Washington Population Change, cont. Kenya has pyramid shape with many young people – rapid growth United States has column shape – slow growth Italy is slightly top-heavy – slow/negative growth

Lesson 2 / ESRM100 / University of Washington The Demographic Transition Stage I - birth and death rates are high until industrialization reduces death rates Stage II - gap between birth and death rates results in high population growth Stage III - birth rate drops toward death rate and population growth declines

Lesson 2 / ESRM100 / University of Washington The Demographic Transition, cont. Some nations are slow to move from stage II to stage III Medical advances can affect the demographic transition by decreasing death rates

Lesson 2 / ESRM100 / University of Washington Longevity and Its Effect on Population Growth The maximum lifetime (longevity) is the genetically determined maximum possible age to which an individual can live. Life expectancy is the average number of years an individual can expect to actually live. The human population has grown despite little or no change in longevity.

Lesson 2 / ESRM100 / University of Washington Limiting Factors to Population Growth Short-term factors: drought, disruption to energy supply, disease Intermediate-term factors: desertification, pollutants, disruption to supply of non-renewable resources Long-term factors: Soil erosion, groundwater, climate change

Lesson 2 / ESRM100 / University of Washington Quality of Life and the Human Carrying Capacity of the Earth What is the human carrying capacity of Earth? Logistic curve predictions Packing space Deep Ecology – moral imperative to preserve the biosphere by limiting human population The higher the quality of life, the lower the Earth’s carrying capacity

Lesson 2 / ESRM100 / University of Washington How Can We Achieve Zero Population Growth? Raise the age of first childbearing Social pressures to delay marriage Birth control Breast feeding Family planning

Lesson 2 / ESRM100 / University of Washington National Programs to Reduce Birth Rates The first country to adopt an official population policy was India in Many countries now have a family-planning program. China has one of the oldest and most effective family- planning programs: encourages couples to have only one child. relies on education, family planning control, and a system of rewards and penalties. Should governments force people to limit family size?

Lesson 2 / ESRM100 / University of Washington How Many People Can Earth Support? Estimates range from 2.5 billion to 40 billion. Critical factors are Food supply Land and soil resources Water resources Population density Technology

Chapter 2: Human Population Growth Questions? your TA.