HUMAN POPULATION DYNAMICS opr.princeton/popclock/

1. HUMAN POPULATION DYNAMICShttp://opr.princeton.edu/popclock/

2. Demography The study of human populations along with their characteristics and changes.

3. Core Case Study: Are There Too Many of Us? • The debate over interactions among population growth, economic growth, politics, & moral beliefs is one of the most important & controversial issues in environmental science. • Each week about 1.6 million people are added to the global population. • Most of it in developing countries, leading to the question of whether there are enough resources to provide an adequate standard of living for this growing human population.

4. Core Case Study: Are There Too Many of Us? • Some argue that there are enough resources to support a growing population, and that technological advances will allow for even more growth. • Others argue that environmental degradation may increase, and that rising death rates may be a consequence of an increasing population.

5. Core Case Study: Are There Too Many of Us? • Much of the world’s population growth occurs in developing countries like China and India. Figure 6-1

6. SCIENCE FOCUS: How Long Can the Human Population Keep Growing? • Human activities have directly affected about 83% of the Earth’s land surface (excluding Antarctica). • Humans have altered nature in eight major ways: • They have reduced biodiversity, increased primary productivity, increased genetic resistance in pests, eliminated natural predators, introduced harmful species, used renewable resources unsustainably, interfered with chemical cycling and energy flow, and relied on fossil fuels.

7. [6-1] How Many People Can the Earth Support? • The human population has grown rapidly due to technology, improved medical techniques, emphasis on hygiene, and expansion of agriculture and industry. • World’s exponential growth rate is around 1.22% a year. • Geographically, this growth is unevenly distributed: • Developed countries grow at 0.1% per year. • Developing countries grow 15 times faster at 1.5% per year.

8. [6-1] How Many People Can the Earth Support? • Population growth has slowed but is troubling because we do not know how long we can continue without overshooting earth’s carrying capacity for humans.

9. Where Are We Headed? • U.N. world population projection based on women having an average of 2.5 (high), 2.0 (medium), or 1.5 (low) children. The most likely projection is the medium one—9.3 billion by 2050.

10. [6-1] How Many People Can the Earth Support? • No population, including humans, can continue to grow indefinitely; there are limits on population growth: • The intrinsic rate of increase (r) orbiotic potential is the maximum rate at which a population would grow if it had unlimited resources. • All of the limiting factors that act together to limit the growth of a population is environmental resistance. • Carrying capacity(K): the maximum population of a given species that a particular habitat can sustain indefinitely without degrading the habitat.

11. 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. • Exponential growth (J-curve) is converted to logistic growth (S-curve), in which the growth rate decreases as the population becomes larger and faces environmental resistance.

12. Logistic Growth of a sheep population on the island of Tasmania between 1800 & 1925 • As a population levels off, it often fluctuates slightly above and below the carrying capacity.

13. Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size • Over time species may increase their carrying capacity by developing adaptations. • Some species maintain their carrying capacity by migrating to other areas. • So far, technological, social, and other cultural changes have extended the earth’s carrying capacity for humans.

14. Population Density and Population Change: Effects of Crowding • Population density: the number of individuals in a population found in a particular area or volume. • A population’s density can directly affect how rapidly it can grow or decline = density dependent. • e.g. biotic factors like disease & food availability • Some population control factors are not affected by population density = density independent . • e.g. abiotic factors like weather or fire

15. Reproductive Patterns:Opportunists vs. Competitors • Large number of smaller offspring with little parental care (r-selected species). • Fewer, larger offspring with higher invested parental care (K-selected species). • Positions of r-selected and K-selected species on the sigmoid (S-shaped) population growth curve.

16. Reproductive Patterns • r-selected species tend to be opportunists while K-selected species tend to be competitors.

17. [6-2] What Factors Influence the Size of the Human Population? • Population increases through births and immigration and decreases through deaths and emigration. • The crude birth rate (natality) is the number of live births per 1,000 people in a population in a specific year. • The crude death rate (mortality) is the number of deaths per 1,000 people in a population in a specific year.

18. [6-2] What Factors Influence the Size of the Human Population? • The populations of China and India comprise 37% of the world’s population. The next most populated country is the United States with 4.5% of the world’s population.

19. The world’s 10 most populous countries in 2008 with projections in 2025.

20. [6-2] What Factors Influence the Size of the Human Population? • Fertility rate is the number of births that occur to an individual woman or in a population. • The changing nature of fertility rates affects population growth. • Replacement-level fertility is the number of children needed to replace their parents. • Total fertility rate (TFR) is the average number of children that a woman has during her reproductive years.

21. Case Study: U.S. Population Is Growing Rapidly • The population of the United States grew from 76 million in 1900 to 304 million in 2008. • Although a drop in TFR has slowed the country’s growth, it is still growing faster than any other developed country (someone migrating to the U.S. every 32 seconds) . • Because of high per capitaresource use and waste, growth in the United States has an enormous environmental impact.

22. Per Capita • Per individual or per person. • Formula for determining resource use per person for an area. Gross National Product - The most commonly used measure of the economic growth of a country.

23. Environmental Impact • The environmental impact (I) of a population on a given area depends on 3 key factors: • number of people (P). • average resource use per person (affluence, A). • beneficial/harmful effects of technologies (T) used to provide/consume each unit of a resource and control/prevent resulting pollution & environmental degradation.

24. Environmental Impact Equation (Paul Ehrlich Formula) population X affluence X technology = Environmental Impact I = P x A x T

25. Developing Countries • Population size & the resulting degradation of renewable resources (as the poor struggle to stay alive) tend to be the key factors in total environmental impact. • Resource use per person is low.

26. Developed Countries • High rates of resource use (affluenza). • Result in high levels of pollution and environmental degradation per person. • A U.S. citizen consumes 30 times more than the average citizen of India and 100 times more than the average person in the world’s poorest countries. • Thus, poor parents in a developing country would need 60-200 kids to have the same lifetime environmental impact as 2 typical U.S. kids!

27. [6-2] What Factors Influence the Size of the Human Population? • Many factors influence birth and fertility rates. • More children work in developing countries; they are important to the labor force. • The economic cost of raising and educating children determines their numbers. • If there are available private/public pension systems, adults have fewer children because they don’t need children to take care of them in old age. • People in urban areas usually have better access to family planning, so have fewer children.

28. [6-2] What Factors Influence the Size of the Human Population? • If women have educational and economic choices, they tend to have fewer children. • When the infant mortality rate is low, people have fewer children. • The older the age at which women marry, the fewer children they bear. • If abortions are available and legal, women have fewer children. • The availability of reliable birth control allows women to space children and determines the number of children they bear.

29. [6-2] What Factors Influence the Size of the Human Population? • Factors that have caused a decline in death rates are the following: • Better food supplies and nutrition, and safer water supplies contribute to people living longer. • Advances in medicine and public health, and improved sanitation and personal hygiene also contribute to people living longer.

30. 47 years Life expectancy 77 years 8% Married women working outside the home 81% 15% High school graduates 83% 10% Homes with flush toilets 98% 2% Homes with electricity 99% 10% Living in suburbs 52% 1900 Hourly manufacturing job wage (adjusted for inflation) $3 2000 $15 1.2 Homicides per 100,000 people 5.8 Fig. 6-6, p. 128 Some major changes that took place in the United States between 1900 and 2000.

31. [6-2] What Factors Influence the Size of the Human Population? • Measures of overall health are: • Life expectancyis the average number of years a newborn can expect to live. • Infant mortality rate is the number of babies out of every 1,000 born who die before their first birthday. • This rate reflects a country’s level of nutrition and health care. • It is the single best measure of a society’s quality of life.

32. [6-2] What Factors Influence the Size of the Human Population? • U.S. infant mortality rate is higher than 40 other countries because: • Inadequate health care for poor women and for their babies. • Drug addiction among pregnant women. • High birth rate among teenagers.

33. [6-2] What Factors Influence the Size of the Human Population? • Migration is also a factor in population change. • Historically, the United States has admitted more immigrants than all other countries combined. • Some 60% of the U.S. population supports limiting legal immigration. • A recent study suggests that to maintain a viable workforce as baby boomers retire, the U.S. would have to absorb many more immigrants per year than it currently does. • However, a reduction in immigration may help mediate the enormous environmental footprint the United States currently has.

34. Case Study: U.S. Immigration • Since 1820, the U.S. has admitted almost twice as many immigrants and refugees as all other countries combined. Figure 6-7

35. [6-3] How Does a Population’s Age Structure Affect Its Growth or Decline? • Age structure diagrams (histograms) are visual aids that show the distribution of males and females in each age group; how fast a population grows or declines depends on its age structure.

36. [6-3] How Does a Population’s Age Structure Affect Its Growth or Decline? • The percentages of males and females in the total population are divided into the following age categories: • Pre-reproductive ages span birth to 14 years of age. • Reproductive ages include age 15 through 44. • Post-reproductive ages include ages 45 and up.

37. [6-3] How Does a Population’s Age Structure Affect Its Growth or Decline? • The major determining factor in a country’s future population growth is the number of people under the age of 15. • In 2008, 28% of the planet’s population was under 15. • Populations with a large proportion of its people in the pre-reproductive age group have a large potential for rapid population growth.

38. POPULATION AGE STRUCTURE Male Female Male Female Male Female Male Female Expanding Rapidly Guatemala Nigeria Saudi Arabia Expanding Slowly United States Australia China Stable Japan Italy Greece Declining Germany Bulgaria Russia Postreproductive ages 45–85+ Prereproductive ages 0–14 Reproductive ages 15–44 Fig. 6-8, p. 131

39. 30% (with 41% in Africa) of the people in developing countries were under 15 years old in 2008 versus only 17% in developed countries. • The youthful age structure of most developing countries contributes to an unemployment crisis. Figure 6-9

40. Expansive/rapid growth: birth rate exceeds the death rate, population is getting larger, and pyramid-shaped histogram. Ex’s. Kenya, Nigeria, Guatemala, Saudi Arabia

41. Slow growth/stable (zero growth): birth rate almost equals death rate, population is not getting any larger or is growing very slowly, and histogram shape is straighter and more box-like until around age 45-85. Examples of slow growth: U.S., Australia, China, Canada Examples of zero (stable) growth: Spain, Portugal, Greece, Japan, Italy

42. Declining (negative growth): when the birth rate is smaller than the death rate, and the pyramid bulges near the top or is inverted. Examples: Germany, Bulgaria, Russia, Hungary

43. [6-3] How Does a Population’s Age Structure Affect Its Growth or Decline? • Changes in the distribution of a country’s age groups have long-lasting economic and social impacts. An example of this is the ‘baby boom’ generation in the U.S. • Such a group can dominate the population’s demands for goods and services. • They influence elections and legislation and economic demand. • Retirement of baby boomers in the U.S. may create a shortage of workers.

44. POPULATION AGE STRUCTURE • Tracking the baby-boom generation in the United States. Figure 6-10

45. [6-3] How Does a Population’s Age Structure Affect Its Growth or Decline? • The “baby bust” generation compared to that of the “baby boom”: • There will be fewer people to compete for education, jobs, and services. • Too few people in the labor force may increase wages. • It may be more difficult to get job promotions because a larger baby-boom group will occupy most upper-level positions. • These fluctuations in population age structure have social and economic effects for decades.

46. [6-3] How Does a Population’s Age Structure Affect Its Growth or Decline? • Reduced fertility and population decline can have long-term consequences, especially if the decline is rapid. • With a gradual population decline, its harmful effects can usually be managed. • When there’s a sharp rise in the proportion of older people: • Produces a sharp rise in public service costs, for health, etc. • May have many fewer working taxpayers and labor shortages. • It may be necessary to raise retirement age, raise taxes, cut retirement benefits, and increase legal immigration, which are generally unpopular moves.

47. [6-3] How Does a Population’s Age Structure Affect Its Growth or Decline? • If population declines because of deaths, consequences are serious: • Deaths from disease such as AIDS disrupt a country’s social and economic structure. • Large numbers of people in a particular age group are removed from the country’s future. • Life expectancy drops. • In the case of AIDS, the deaths are mostly young adults, those who usually help run the country and everyday life for millions. • Two major goals are to reduce the spread of HIV through education and health care and to provide financial help for education, health care, and volunteer teachers and social workers to compensate for the lost young adults.

48. Some Problems with Rapid Population Decline Can threaten economic growth Labor shortages Less government revenues with fewer workers Less entrepreneurship and new business formation Less likelihood for new technology development Increasing public deficits to fund higher pension and health-care costs Pensions may be cut and retirement age increased Fig. 6-11, p. 133

49. [6-4] How Can We Slow Human Population Growth? • Experience indicates that the most effective ways to slow human population growth are to encourage family planning, to reduce poverty, and to elevate the status of women.

50. [6-4] How Can We Slow Human Population Growth? • The demographic transition hypothesis states that as countries become industrialized, first their death rates and then their birth rates decline; this transition takes place in 4 distinct stages: • Preindustrial stage: little population growth due to the high infant mortality & high death rate. • Transitional stage: industrialization begins & pop. grows rapidly—death rate drops and birth rates remain high. • Industrial stage: pop. growth slows—birth rate drops and approaches death rate—improved food production, health, & education. • Postindustrial stage: pop. growth levels off & then declines as birth rates fall below death rates.