Lecture Outline - Chapter 35

35.1. Exponential Population Growth

1. The human growth curve is J-shaped. (Fig. 35.1)
   • a. Initially, growth is very slow but as more reproducing individuals are added, curve begins to slope steeply upward.
   • b. Figures show rapid growth accelerating, adding numbers equal to a 200,000 population city each day. (Fig. 35.2)
   • c. Exponential growth adds up similar to compound interest.
   • d. Growth rate is calculated each year; hypothetical population increases in larger added numbers even though growth rate decreases from 2% to 1.99% because the world population is growing larger. (Fig. 35.1)
2. Growth Rate Depends on Births Versus Deaths (p. 693)
   • a. Determined as difference between number of persons born (birthrate, or natality) and number of persons who die (death rate, or mortality) per year per 1,000 persons; i.e., Canada has birthrate of 14 per 1,000 per year and death rate of 7 per 1,000 per year for a growth rate of 7 per 1,000 or 0.7%.
   • b. From 1750 to 1965, world population growth rate grew to become 2.0% per year, then declined to 1.6% although this still adds even more per year.
3. Doubling Time Depends on Growth Rate
   • a. Calculated by the formula: d = 70 ÷ gr where d = doubling time, 70 = demographic constant, and gr = growth rate (%).
   • b. If present world growth rate of 1.6% continues, world population will double in 44 years, also requiring double the jobs, water, energy, etc.
   • c. Time interval needed to add an additional billion people to the world population has become shorter.
4. If growth rates continue to decline, growth beyond 5.5 billion may eventually level off at 8, 10.5, or 14.2 billion, depending on rate of decline.
5. Carrying Capacity Limits Population Size
   • a. Growth curve for nonhuman populations is S-shaped. (Fig. 35.2)
   • b. Beginning stage is small since numbers are minimal despite growth.
   • c. Soon organisms realize maximum growth rate under ideal conditions; food and space are initially plentiful.
   • d. Environmental resistance (such as lack of space, food, and build up of waste) soon opposes biotic potential and includes all factors that cause early death of organisms; prevents population from producing maximum number of organisms.
   • e. Carrying capacity of the environment is the maximum population that the environment can support for an indefinite period; it is a compromise between biotic potential and environmental resistance.
   • f. Some believe earth could support 50-100 billion people; others believe we have already exceeded the limit if a minimal quality of life is expected.

1. Three periods of exponential growth occurred in human history following toolmaking, agricultural revolution, and industrial revolution.
2. More-Developed versus Less-Developed Countries
   • a. Countries of the world are divided into two groups. (Fig. 35.3)
   • b. More-Developed countries (MDCs)
     • i. Includes countries in North America and Europe, Japan, New Zealand, etc.
     • ii. A majority of people enjoy a good standard of living.
     • iii. Population growth is under control.
     • iv. Generally doubled their populations between 1850 and 1950 due to decline in death rate.
     • v. Decline in birthrate followed; result is very modest growth rate and a demographic transition; some even have negative growth.
   • c. Less-developed countries (LDCs)
     • i. Includes countries in Latin America, Africa, Asia, etc.
     • ii. Vast majority of people lie in poverty.
     • iii. Population growth is out of control.
     • iv. Growth rate peaked in 1960-65; expected to drop from 2.5% to 1.8% by 2000; populations will expand from 4.4 billion to 10.2 billion by 2100.
3. Strategies for Slowing Growth Rate
   • a. Strengthen family planning programs; provision of contraception to women who want it could lower 2100 prediction from 10.2 billion to 8.3 billion.
   • b. Providing education of children, reducing child mortality and raising status of women reduces the desire for large families.
   • c. Delaying average onset of childbearing by five years could drop 2100 prediction from 10.2 billion to 6.1 billion.
4. Comparing Age Structure
   • a. LDCs have "population momentum" because more women are entering reproductive years than leaving them.
   • b. Populations have three age groups: dependency, reproductive, and postreproductive that can plot age structure of a country. (Fig. 35.4)
   • c. Zero population growth does not occur just because each couple has two children or less.
   • d. Replacement reproduction is exceeded when more young women enter reproductive years than older women leave them; causes positive growth rate.
   • e. Since most LDCs have large proportion younger than age 15, their populations will expand greatly even with replacement reproduction.

1. Pollutants are substances added to the environment that lead to undesirable effects for life.
2. Air Pollution (Fig. 35.5)
   • a. Primary causes of air pollution are fossil fuel burning and vehicle exhaust.
   • b. Four major concerns related to air pollutants are:
     • i. Global warming: a rise of over 0.5^oC by the year 2020 would cause sea levels to rise, coastal flooding, food loss due to climate changes, etc.
     • ii. Destruction of the ozone shield that protects us from ultraviolet light. (Fig. 35.7)
     • iii. Acid deposition from burning coal and nitrogen oxides from automobile exhausts are converted to acids when combined with water vapor in the atmosphere; acid deposition is associated with dying lakes and forests, corrosion of marble, etc., and degradation of water supplies. (Fig. 35.8)
     • iv. Photochemical smog contains nitrogen oxides and hydrocarbons, which react with one another in sunlight; affects breathing and results in decreased plant growth and leaf mottling; becomes severe during thermal inversions. (Fig. 35.9)
3. Water Use and Pollution (p. 701)
   • a. Main fresh water uses: domestic and drinking water, crop irrigation, industrial use, and energy production. (Fig. 35.10)
   • b. Source of fresh water is rivers, lakes and underground aquifers.
   • c. Mining of underground water may exceed replacement by 50 times in Midwest; aquifers in China can only sustain 650 million of over 1.1 billion people.
   • d. Pollution of surface, ocean, and groundwater also reduces availability.
4. Surface Water Pollution
   • a. Various sources pollute surface water. (Fig. 35.11)
   • b. Sewage treatment degrades organic wastes that otherwise causes oxygen depletion; lack of oxygen reduces diversity of life.
   • c. Human feces can also contain pathogenic microorganisms causing cholera, typhoid fever, dysentery.
   • d. Cultural eutrophication occurs when fertilizer run-off and soil erosion enter surface water causing overgrowth of algae; algae die, decomposers use up oxygen cause massive fish kills.
   • e. Acids washed from atmosphere cause lakes to become sterile by leaching aluminum and iron from soil; these ions kill aquatic life; lime may help neutralize acidity.
5. Groundwater Pollution (p. 701)
   • a. Ammonium (NH₄⁺) released from animal and human wastes is converted by soil bacteria to soluble nitrates and percolates into underground water supplies; affecting 5-10% of all U.S. wells.
   • b. Disposal of industrial wastes in aquifers is being phased out; it is hard to find alternatives for disposing of wastes, prevention of waste production is higher priority.
6. Pollution of the Oceans (p. 702)
   • a. Coastal ecosystems may be damaged by sewage disposal and dumping of wastes at sea which wash back to shore.
   • b. Offshore mining and shipping add five million metric tons of oil per year.
   • c. Oil spills may be accidental, as in the Exxon Valdez spill in 1989 at Alaska's Prince William Sound, or intentional environmental terrorism, as the oil released during the Persian Gulf War.
7. Losing Marine Biodiversity
   • a. Pollution has contributed to decline in ocean quality and habitats.
   • b. Haddock was once most-abundant species; now accounts for less than two percent of total catch.
   • c. Cod and bluefin tuna populations have declined 90%.
   • d. Coral reefs are overgrown with algae; fish that normally control algae have been killed off.
8. Land Pollution (p. 704)
   • a. In 1950, 20% of world's population lived in cities; in 2000, 60% will be in cities.
   • b. Expansion of human populations includes urban sprawl and encroachment on agricultural land.
9. Waste Disposal and Dangerous Trash
   • a. Solid wastes include household trash, sewage sludge, agricultural residues, mining refuse, and industrial wastes.
   • b. Landfills, incineration, and open dumping are becoming more expensive.
   • c. Recycling holds promise of reducing waste disposal problem, increasing jobs.
10. Hazardous Wastes
    • a. Heavy metals, chlorinated hydrocarbons, and other wastes may enter water.
    • b. Biological magnification occurs when chemicals become more concentrated passing along a food chain. (Fig. 35.12)
    • c. Prevention ($200 million/year) is cheaper than cleanup ($9 billion/year).
11. Soil Erodes and Deserts Grow
    • a. Soil erosion occurs when wind and rain carry away topsoil; current rate is about 25 billion tons per year worldwide.
    • b. Erosion in return requires compensation by fertilizers, pesticides, and fossil fuels to maintain productivity.
    • c. Strip-cropping and contour farming are effective soil conservation measures. (Fig. 35.13)
    • d. Desertification
      • i. Occurs when marginal land is transformed into desert conditions because of overgrazing and overfarming.
      • ii. Most serious at edge of Sahara Desert in Africa; 350,000 square miles of grazing land became desert in 50 years.
12. Losing Terrestrial Biodiversity
    • a. Loss of habitat due to human encroachment is chief cause of biodiversity decline.
    • b. Wars Cause Land Spoilage
      • i. Civil war in Angola caused rhino and elephant slaughter to secure tusks and horns to sell to buy uniforms and weapons.
      • ii. In war between Uganda and Tanzania, hippos were used for target practice.
      • iii. Habitat destruction is more devastating; estimated 5.45 million acres of Vietnam defoliated by spraying Agent Orange, decimating half of Vietnam wetlands.
      • iv. Persian Gulf War seriously disrupted desert and shoreline ecosystems.
13. Deforestation of Coniferous and Tropical Forests (p. 705)
    • a. In Canada, paper and wood industry requires logging to provide hardwoods for export.
    • b. Tropical forests have much higher diversity of species; loss of unit area in tropics is far greater loss of species.
    • c. Slash-and-burn agriculture is used in Brazil's Amazon rainforests; fertility of exposed land is short-lived.
    • d. When farm cropland deteriorates, cattle ranching moves in.
    • e. New pig-iron industry must use charcoal before product is exportable.

1. Environmental degradation was often viewed as unavoidable consequence of economic growth; wise use of local resources may allow economic development based on native resources such as jungle herbs, with higher income than from modern lumbering or cattle ranching.
2. Growing population stresses environment by increasing consumption and increasing pollution; average U.S. family uses 30 times resources used by LDC family.
3. Modern society lives on borrowed carrying capacity by using fossil fuels and degrading the environment in ways that must be paid for by future generations.
4. Overpopulation and overconsumption contribute to pollution and mass extinction of wildlife.
5. Philosophy of sustainable growth can achieve economic growth without problems of environmental degradation by developing recycling programs, decreasing energy consumption, and protecting the environment.