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Environmental Science

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Presentation on theme: "Environmental Science"— Presentation transcript:

1 Environmental Science
Chapter 9 Lecture Notes The Human Population Introduction to Human Population Growth (11")

2 Chapter 9 Targets 1. I can define demography and describe the 2 general categories of population growth they study. 2. I can describe how the size and growth rate of the human population has changed in the last 200 years. 3. I can make predictions about population trends based on age structure. 4. I can describe how survivorship, fertility, migration, death rate and life expectancy affect populations. 5. I can describe the four stages of the demographic transition. 6. I can name the 2 main factors affecting birth rates.

3 Studying Human Populations
Demography: study of HUMAN populations Countries based on 2 population trends: Developed and Developing countries. Developed countries have:  average incomes  industrial economies  social support systems  population growth Developing countries have:  average incomes simple and agriculture-based economics  population growth T1

4 The Human Population Over Time
Human population underwent exponential growth in the 1800s. WHY? Better food production and hygiene came with the industrial and scientific revolutions

5 Age Structure T3 Age structure/Population Pyramid: classifies a population into groups by age age helps demographers make predictions Countries with high growth rates usually have more young than old people Countries with slow growth or no growth usually have an even distribution of ages in the population Ethiopa Russia United States

6 Survivorship T4 Survivorship: % of newborns in population expected to survive to a given age used as another way to predict population trends (see video) Which survivorship curve would belong to humans? Frogs? Robins?


8 Fertility Rates T4 Fertility rate: number of births (per year) per 1,000 women of childbearing age (usually 15 to 44) Replacement level: average number of children each parent must have in order to “replace” themselves This number is slightly more than 2 because not all children born will survive and reproduce

9 Migration T4 Migration: movement of individuals or populations from one location to another Immigration vs. Emigration Populations of many developed countries might be decreasing if not for immigration

10 Declining Death Rates Dramatic  in human population in last 200 years
Happened because death rates declined faster than birth rates Death rates declined mainly because more people now have access to enough food, clean water, and safe sewage disposal Discovery of vaccines in 20th century also contributed to declining death rates

11 Life Expectancy T4 Life expectancy: average length of time an individual is expected to live Life expectancy is most affected by infant mortality, the death rate of infants less than a year old

12 The Demographic Transition
Demographic transition: general pattern of demographic change from high birth/death rates to low birth/death rates Seen during history of more-developed countries Stages of Demographic Transition Video (1")

13 Stages of Transition First stage: society is preindustrial
Birth/death rates are high and population size is stable Second stage: population explosion occurs Death rates decline as hygiene, nutrition, and education improve. Birth rates remain high, so population grows very fast. Third stage: population growth slows because birth rate decreases Birth rate = death rate, population size stabilizes Fourth stage: birth rate drops below replacement level, population begins to decrease

14 Women and Fertility T6 The factors most clearly related to a decline in birth rates are increasing education and economic independence for women

15 Chapter 9 Targets 7. I can describe three problems caused by rapid human population growth. 8. I can compare population growth problems in more-developed countries and less developed countries. 9. I can analyze strategies countries may use to reduce their population growth. 10. I can describe worldwide population projections into the next century.

16 Problems of Rapid Growth
Rapidly growing population uses resources faster than environment can renew them Living standards drop when wood is removed from local forests faster than it can grow back, or when wastes overwhelm local water sources Symptoms of overwhelming populations include polluted rivers, barren land, inadequate housing, and overcrowded schools

17 A Demographically Diverse World
T8 Least developed countries: identified by U.N. as showing fewest signs of improving income, human resources, and economic diversity Populations are still growing rapidly in less developed countries, with most of the world’s population now in Asia

18 Managing Development and Population Growth
Less developed countries face continued population growth that will prevent them from developing into world economic leaders Countries such as China, Thailand, and India have created campaigns to reduce fertility rates of their citizens These campaigns include public advertising, family planning programs, economic incentives, or legal punishment

19 Managing Development and Population Growth
In 1994, United Nations held International Conference on Population and Development (ICPD) Involved debates about relationships between population, development, and the environment

20 Managing Development and Population
With these goals, worldwide fertility rates are dropping as shown below (see assignment)

21 Projections to 2050 T10 Looking at the graph below, most demographers predict the medium growth rate, and a world population of 9.2 billion in 2050 Current population is at 7 billion Population Clock

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