Chapter 6 and 7 Human Population

Nature exists at several levels of complexity

Factors that Regulate Population Abundance and Distribution Population size- the total number of individuals within a defined area at a given time. Population density- the number of individuals per unit area at a given time. Population distribution- how individuals are distributed with respect to one another. Population sex ratio- the ratio of males to females Population age structure- how many individuals fit into particular age categories.

Factors that Influence Population Size Density-dependent factors- the size of the population will influence an individual’s probability of survival. Density-independent factors- the size of the population has no effect on the individual’s probability of survival.

Exponential Growth Model Growth rate- the number of offspring an individual can produce in a given time period, minus the deaths of the individual or offspring during the same period. Intrinsic growth rate- under ideal conditions, with unlimited resources, the maximum potential for growth.

Population Dynamics and Carrying Capacity Population size is governed by births, deaths, immigration, and emigration: [Population Change] = [Births + Immigration] – [Deaths + Emigration] Population Change = (B + I) – (D + E) If the number of individuals added by births and immigration are balanced by those lost by deaths and emigration then there is zero population growth

Exponential Growth Model J-shaped curve- when graphed the exponential growth model looks like this.

Logistic Growth Model Logistic growth- when a population whose growth is initially exponential, but slows as the population approaches the carrying capacity. S-shaped curve- when graphed the logistic growth model produces an “S”.

Variations of the Logistic Model If food becomes scarce, the population will experience an overshoot by becoming larger than the spring carrying capacity and will result in a die-off, or population crash.

Reproductive Strategies K-selected species- the population of a species that grows slowly until it reaches the carrying capacity. Ex. elephants, whales, and humans. R-selected species- the population of a species that grows quickly and is often followed by overshoots and die-offs. Ex. mosquitoes and dandelions

the intrinsic rate of increase (r) is the rate at which a population will grow if it had unlimited resources. Populations with high (r): Reproduce early in life Short generation times Reproduce many times Many offspring each time they reproduce

Carrying Capacity There are always limits to population growth in nature. Carrying capacity (K) is the number of individuals that can be sustained in a given space If the carrying capacity for an organism is exceeded, resources are depleted, environmental degradation results, and the population declines.

Exponential vs. Logistic Growth Exponential growth occurs when resources are not limiting. Logistic growth occurs when resources become more and more limiting as population size increases.

Exponential Population Growth Resources are not limiting. Population size increases faster and faster with time Currently the human population is undergoing exponential growth Cannot occur forever because eventually some factor limits population growth

Logistic Population Growth Occurs when the population growth rate decreases as the population size increases. Note that when the population is small the logistic population growth curve looks like exponential growth over time, the population size approaches a carrying capacity (K).

Exceeding the Carrying Capacity During the mid–1800s sheep populations exceeded the carrying capacity of the island of Tasmania. This "overshoot" was followed by a "population crash". Numbers then stabilized, with oscillation about the carrying capacity.

Exceeding the Carrying Capacity Reindeer introduced to a small island off of Alaska in the early 1900s exceeded the carrying capacity, with an "overshoot" followed by a "population crash" in which the population was totally decimated by the mid– 1900s.

Survivorship Curves Three kinds of curves: Late loss (usually K– strategists) in which high mortality is late in life Constant loss (such as songbirds) in which mortality is about the same for any age Early loss (usually r– strategists) in which high mortality is early in life

Scientists Disagree on Earth’s Carrying Capacity Figure 7.1

Scientists Disagree on Earth’s Carrying Capacity The following graphs show theoretical models of food supply and population size.

Factors that Drive Human Population Growth Demography- the study of human populations and population trends. Changes in Population Size Fertility Life Expectancy Age Structure Migration

Changes in Population Size Immigration - the movement of people into a country Emigration - the movement of people out of a country. Net migration rate- the difference between immigration and emigration in a give year per 1,000 people in the country.

Changes in Population Size Crude birth rate (CBR)= the number of births per 1,000 individuals per year. Crude death rate (CDR)= the number of deaths per 1,000 individuals per year. Global population growth rate = (CBR- CDR)/ 10 National population growth rate = (CBR+ immigration) - (CDR + emigration)/ 10 Doubling time (in years)- 70/growth rate

Factors Affecting Human Population Size Zero Population Growth (ZPG) – when births plus immigration equal deaths plus emigration Crude Birth or Death Rate - # births or deaths /1,000 people U.S. CBR – U.S. CDR – 8.38

World Population Rate of World's Population Change (%) (Birth Rate – Death Rate)/1000 people x 100 Average Annual population growth rate 1.2% (global).963% (U.S.) World Population = 7.2 billion (video)(video) China and India - 37% of world's population U.S. – 4.5% of world's population U.S. Population = 312 million

Global Fertility Rates (2 types) 1. Replacement Level Fertility Number of children a couple must have to replace themselves (2.1 in developed countries and 2.5 in developing countries) greater than 2 because some female children die before reaching their reproductive years Population Momentum – The continued growth of a population after reaching replacement level resulting from a large number of people entering their childbearing years

Global Fertility Rates (2 types) 2. Total Fertility Rate (TFR) most useful for projecting future population change the average number of children a woman will have during her childbearing years 2000 World: 2.9 (1.3 developed, 3.2 developing) U.S.: World: 2.46 U.S.: 2.06

U.S. Growth US - highest fertility rate and highest immigration rate of any industrialized country – Why? 1.66 million more births than deaths; 800,000 legal immigrants; 300,000 illegal immigrants ***Because of the high per capita rate of resource use in the US, each addition to the US pop. has an enormous environmental impact!!

U.S. Growth 392 million by more than a 50 % increase from the 1990 population size Reasons for Projected Growth: Increase in number of unmarried mothers (including teenagers) Continued higher fertility rates for women in some racial and ethnic groups than for Caucasian women High levels of legal and illegal immigrants (43% of US pop. growth) Inadequate family-planning services

What factors affect Birth and Fertility Rates? Average level of education and affluence Importance of children as part of the labor force Urbanization Cost of raising and educating children Educational and employment opportunities for women

6. Infant mortality rate 7. Average age at marriage 8. Availability of private and public pension systems 9. Availability of legal abortions 10. Availability of reliable methods of birth control 11. Religious beliefs, traditions and cultural norms

Life Expectancy Life expectancy- the average number of years that an infant born in a particular year in a particular country can be expected to live, given the current average life span and death rate of that country.

Life Expectancy Infant mortality rate- the number of deaths of children under 1 year of age per 1,000 live births. Child mortality rate- the number of deaths of children under age 5 per 1,000 live births.

What factors affect death rates? Decline in the CDR (crude death rate) has led to the rapid increase in world's population. People started living longer! “It's not that people stopped breeding like rabbits; it's just that they stopped dying like flies” (UN)

2 Indicators of Overall Health 1. Life expectancy (the avg. number of years a newborn infant can expect to live) 75 years (developed countries) 64 years (developing countries) U.S years (2011) Angola – years

2 Indicators of Overall Health 2. Infant mortality rate - the number of babies out of every 1000 born each year that die within 1 year The single most important measure of a society's quality of life –it reflects the general level of nutrition and health care

U.S. Infant Mortality Rate deaths/1,000 live births These rates are high because: inadequate health care (poor women) drug addiction (among pregnant women) high birth rate among teenage women Babies born to teenage women are more likely to have low birth weights – the most important factor in infant deaths US – highest teenage pregnancy of any industrialized country US What is your life expectancy? (worksheet)

Miniature earth video clip

Age Structure Age structure diagrams (population pyramids)- visual representations of age structure within a country for males and females.

Age Structure Diagrams Show the proportion of the population at each age level Three main age categories: Prereproductive (ages 0-14) Reproductive (15-44) Postreproductive (45+)

Age Structure Diagrams

How can Age Structure Diagrams be used to make population and economic projections? Baby-Boom Generations Creates social and economic changes that ripple through a society for decades Competition for jobs; political clout; retirement benefits and needs

What are the effects of population decline? Rapid population decline can lead to severe economic and social problems A sharp rise in proportion of elderly will lead to a large share of medical care, social security and other costly social services Labor shortages

The Demographic Transition The theory of the demographic transition is the theory that as a country moves from a subsistence economy to industrialization and increased affluence, it undergoes a predictable shift in population growth.

The Stages of the Demographic Transition Phase 1: Pre-industrial: Slow population growth because there are high birth rates and high death rates which offset each other. Phase 2: Transitional: Rapid population growth because birth rates remain high but death rates decline due to better sanitation, clean drinking water, increased access to food and goods, and access to health care. Phase 3: Industrial: Stable population growth as the economy and educational system improves and people have fewer children. Phase 4: Post industrial: Declining population growth because the relatively high level of affluence and economic develop encourage women to delay having children.

Should we reduce births? Can we provide enough food, energy, water, sanitation, education, health care, and housing for twice as many people if the world population continues to grow? Can we provide adequate standard of living for twice as many people without causing massive environmental damage? Some say the Earth is already overpopulated Others say the Earth could support billion people if everyone existed at a minimal survival level (grain diet only, cultivate all arable land, mine the Earth's crust to a depth of 1 mile)

Family Planning Family planning- the regulation of the number or spacing of offspring through the use of birth control.

Ways to Reduce Births Family Planning How many children and when to have them Contraceptives (55% drop in TFR in developing countries) Economic Rewards and Penalties higher taxes, other fees, elimination of tax deductions for a third child, lose health care benefits, food allotments and job options Work best if they encourage rather than mandate Empowering Women Education, jobs, rights

The 12 Most Populous Countries in the World

The relationship between economic development and population growth rate for developing nations.

Ecological Footprints Affluence - having a lot of wealth such as money, goods, or property.