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Chapter 5. The Human Population. From Raven & Berg – Chapter 8. Population biology . Principles of Population Ecology. The size of the human population is central to many environmental problems and their solutions Important that we understand how populations increase or decrease

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chapter 5

Chapter 5

The Human Population

principles of population ecology
Principles of Population Ecology
  • The size of the human population is central to many environmental problems and their solutions
    • Important that we understand how populations increase or decrease
    • Population – a group of organisms of the same species that live in the same geographical area at the same time
population ecology
Population Ecology
  • Deals with the number of individuals of a particular species that are found in an area and how and why those numbers increase or decrease
    • Population ecologists try to determine the population processes that are common to all populations
      • Which we will apply to chapter 5 in our text book (Human Populations)
aspects of population ecology
Aspects of Population Ecology
  • Study how a population competes for food or other resources
  • How predation, disease, and other environmental pressures affect the population
  • Reproductive success or failure
maximum population growth
Maximum Population Growth
  • The maximum rate at which a population could increase under ideal conditions is known as its biotic potential, or intrinsic rate of increase.
  • Different organisms have different biotic potentials
factors that affect biotic potential
Factors That Affect Biotic Potential
  • Age at which reproduction begins
    • Reproducing earlier in life has the greatest effect on biotic potential
  • Duration of when organism is capable of reproduction
  • Number of reproductive periods per lifetime
  • Number of offspring produced during each period of reproduction
    • Factors are called life history characteristics
reproductive strategies
Reproductive Strategies
  • r – selected species
    • Have traits that contribute to a high population growth rate
      • (r designates growth rate)
    • Small body size, early maturity, short life span, large broods, and little or no parental care are typical of many r strategists
    • Usually opportunists, found in variable, temporary, or unpredictable environments
    • Probability of long term survival is low
reproductive strategies1
Reproductive Strategies
  • K – selected traits
    • Traits maximize the chance of surviving in an environment where the number of individuals (N) is near the carrying capacity (K) of the environment.
      • Do not produce large numbers of offspring
      • Have long life spans with slow development
      • Late reproducing
      • Large body size
      • Typically invest in parental care of their youngsters
  • Ecologists construct life tables for plants and animals that show the likelihood of survival for individuals at different times during their lives.
  • Survivorship is the probability that a given individual in a population will survive to a particular age
type iii survivorship
Type III Survivorship
  • The probability of death is greatest early in life
  • Those individuals that avoid death, subsequently have a high probability of survival
    • Characteristic of many fish species and oysters
type ii survivorship
Type II Survivorship
  • Intermediate between types I and III.
  • Probability of death is likely across all age groups
    • Results in a linear decline in survivorship
      • This results from the essentially random events that cause death with little age bias
        • This curve is rare, some lizards have a type II survivorship
type i survivorship
Type I Survivorship
  • Exemplified by humans and elephants
  • The young (pre-reproductive) and those at reproductive age have a high probability of living
  • Probability of survival decreases more rapidly with increasing age
    • Deaths are concentrated later in life.
warm up
  • Define chapter 5 vocabulary terms. Vocab quiz Wednesday
    • Fertility
    • Replacement level fertility
    • Demography
    • Population profile
    • Graying
    • Demographic Transition
      • Phase I, II, III, IV
    • Crude death rate
    • Crude birth rate
    • Doubling time
    • Rule of 70
  • Considering the thousands of years of human history, the recent rapid expansion of the global population is a unique event
  • From the dawn of human history until the beginning of the 1800s population increased slowly
  • It was roughly 1830 before the world population reached 1 billion
  • By 1930, the population had doubled to 2 billion
  • 1975 – 4 billion
  • 1987 – 5 billion
  • 1999 – 6 billion
    • Currently growing at the rate of 76 million people added a year
    • Based on current information, medium projection predicts the world will pass 7 billion in 2012
      • 8 billion – 2024
      • 9 billion - 2047
reasons for patterns of growth
Reasons for Patterns of Growth
  • Flow/fluctuating growth wad due to the prevalence of diseases
  • High reproductive rates were balanced with a high infant mortality rate
    • High birth rate and death rate causes slow population growth
  • Late 1800s
    • Louis Pasteur discovered diseases were caused by infectious agents
      • Organisms transmitted by food, insects, water, rodents
  • Vaccinations were developed
  • Cities and towns began treating driving water
  • Discovery of penicillin in the 1930s
  • Improvements in nutrition
  • 1960s – growth rate peaked at 2.1% increase a year
  • Declines result of decline in total fertility rates
    • Average number of babies born to a woman over her lifetime
      • In 1960s fertility rate was an average of 5.0 children per woman
      • Present value 2.7 children per woman
un population projections
UN Population Projections
  • Demonstrate role played by fertility assumptions
    • Constant projection – 2.6 children
    • Medium projection – assumes decline in fertility rate in developing countries (2.02/woman)
    • High projection – assumes fertility rates ½ child greater than the Medium projection
    • Low projection – assumes fertility rates ½ child less than Medium projection
rich nations poor nations
Rich Nations, Poor Nations
  • The World Bank, and arm of the United Nations, divides the countries of the world into three main economic categories according to average per capita gross national income
high income highly developed industrialized countries
High Income, Highly Developed, Industrialized Countries
  • 971 million in 2003
  • Includes the U.S., Canada, Japan, Korea, Australia, New Zealand, the countries of western Europe and Scandinavia, Singapore, Taiwan, Israel, and several Arab states
    • 2003 gross national income per capita
      • $9,386 and above; average of $28,550
middle income moderately developed countries
Middle Income, moderately developed countries
  • 3 billion in 2003
  • Countries of Latin America, northern and southern Africa, China, Indonesia and other southeastern Asian countries, many Arab states, eastern Europe and countries of the former U.S.S.R
  • 2003 gross national income per capita ranges from $755 to $9,385; average of $1,920
low income developing countries
Low-Income, Developing Countries
  • 2.3 billion
  • Comprises the countries of eastern, western, and central Africa, India, and other countries of Asia, and a few former Soviet republics
  • 2003 gross national income per capita is less than $766
    • Average of $450
  • High income countries make up 15% of world’s population
    • Control 80% of the worlds wealth
      • (calculated on the basis of gross national income)
  • Low income countries make up 37% of the world’s population
    • Control only 3% of the worlds wealth
      • Amounts to a difference in per capita income of 63:1!
human development index
Human Development Index
  • United Nations Development Program (UNDP)
  • Measures general well-being based on more info about literacy, and living standards
    • Makes a more direct measurement of poverty in both LDC and MDC
dimensions of the human poverty index
Dimensions of the Human Poverty Index

Based on information about life expectancy, literacy, and living standards

population growth in rich and poor nations
Population Growth In Rich and Poor Nations
  • More than 98% of the world population growth is occurring in the developing countries
    • 2006 growth rate developed countries – 0.1%
      • Add less than 1 million to the worlds population in a year
    • 2006 growth rate in developing countries – 1.5%
      • Adding 75 million in a year
  • Population growth occurs when births outnumber deaths
    • Total fertility rate
      • average number of children each woman in a population has over her lifetime
    • Replacement level fertility
      • Fertility rate that will just replace the population of the parents
        • 2.1 in developed countries, higher in developing countries which have higher infant/childhood mortality rates
population increase in developed and developing countries
Population Increase in Developed and Developing Countries

Because of higher birthrates, developing countries represent a larger and larger share of the world’s population

different population different problems
Different Population, Different Problems
  • Ecologists Paul Ehrlich and John Holdren proposed a formula to account for the human factors that contribute to environmental deterioration and the depletion of resources
    • Human pressure on the environment was product of three factors
      • Population, affluence, technology
ipat formula
IPAT formula
  • I = P * A * T
  • Environmental Impact (I) is proportional to population (P) multiplied by affluence and consumption patterns (A), and multiplied by the level of technology of the society (T)
demand vs need
Demand vs. Need
  • Most environmental issues are a result of the high consumption associated with affluent lifestyles in developed countries
    • U.S – 5% of worlds population, 24% of global emissions of CO2
  • Developing countries needs include economic growth, more employment, wise leaders, effective public polices, fair treatment by other nations, technological and financial help
  • Developed countries must address issues to achieve sustainability
  • IPAT formula might be modified to
  • I = P * A * T


S stands for stewardly concern and practice

developing countries
Developing Countries
  • Prior to industrial revolution most human population survived through subsistence agriculture
    • Families lived on the land, raised livestock,and produced enough crops for their own consumption
rural populations
Rural Populations
  • 70% of the world’s poor live in rural areas
  • Most are engaged in small-scale agriculture
  • Environmental impacts on population growth of this sect of the population
1 land reform
1. Land Reform
  • Reform system of land ownership
  • Collectivization and ownership by the wealthy are two patterns of agriculture land ownership that have kept rural peoples in poverty
2 intensifying cultivation
2. Intensifying Cultivation
  • Introduction of more highly productive varieties of basic food grains
    • Beneficial effect in supporting growing population
    • Consequences
      • Working the land harder, increasing intensity of grazing
        • Deterioration of soil, decreased productivity, erosion, desertification
3 opening new lands for agriculture
3. – Opening New Lands for Agriculture
  • Means converting natural ecosystems to agricultural production
    • Losing the goods and services those ecosystems were contributing
      • Most of the time the ecosystem converted isn’t suited for agriculture and requires large inputs of water and fertilizer
deforestation in the tropics
Deforestation in the Tropics

Millions of acres of rain forest in Central and South America are being cut down each year to make room for agriculture. Much of this deforestation is done by poor, young people who are seeking an opportunity to get ahead but are untrained and unskilled in the requirements of maintaining tropical soil

4 illicit activities
4. – Illicit Activities
  • People without the money to grow or buy food will resort to desperation
5 emigration and immigration
5. – Emigration and Immigration
  • Low-income country residents believe they can improve their situation by migration to wealthier countries
  • Also immigration occurs to escape civil wars and ethnic persecution
problems with immigration
Problems with Immigration
  • Prejudice against foreigners
  • Refugee camps
    • Diseases and hunger take toll on human life
6 migration to cities
6. – Migration to Cities
  • Move from countryside in search of employment and a better life
  • Most of the net growth of the next 50 years in the developing countries will be absorbed in urban areas
growing cities
Growing Cities

Top 10 world metropolitan areas in 2005.


On the outskirts of Sao Paulo, Brazil. 32% of the cities population lives in these blighted areas

  • America leads the world in consumption of many resources
    • Largest share of aluminum, coffee, corn, lead, oil, oilseeds, natural gas, rubber, tin, and zinc
    • Lead in per capita consumption of meat, paper (725 lbs of paper/year!)
  • Affluence provides benefits such as providing amenities such as safe drinking water, sanitary sewage systems, collection and disposal of refuse
    • Keeps many forms of pollution in check
the dark side
The Dark Side
  • Because the U.S. consumes so many resources, we also lead the world in production of many pollutants
negative aspects of affluence
Negative Aspects of Affluence
  • Worlds wealthiest 20% is responsible for 86% of all private consumption and 80% of world trade
    • Consequences
      • 11 of the 15 major fisheries are exploited
      • Old-growth forests are being cleared in South America
      • Oil spills “by-product” of oil appetite
      • Tropical rain forests being cleared for exotic wood
      • Metals mined
      • Oil extracted
  • Demography
    • Study of collecting, compiling, and presenting information about human population
      • Must consider more than just increase in numbers
      • Must also consider how the number of births ultimately affects entire population over the longevity, or lifetimes, of the individuals
population profiles
Population Profiles
  • Bar graph showing the number or proportion of people (males and females separately) at each age for a given population
    • Data is collected through a census
    • In U.S. an most other countries a census is taken every 10 years
    • FYI – I may also refer to these bar graphs as POPULATION PYRAMIDS in class
age profile for the u s
Age Profile for the U.S.
  • Shoes the age structure of the population
  • Proportion of people in each age group at a given date
    • Different cohorts
boom or bust
Boom or Bust?
  • 1931 -1935
    • Low fertility rate due to Great Depression
  • 1946-1960
    • “Baby boom”
      • Reflection of returning veterans flowing WWII
  • 1961-1976
    • Decline in fertility rates
      • People choose to have fewer children
      • “baby bust”
  • Rise in people born in more recent years is “baby boom echo”
The changes in fertility led to the baby boom and baby bust in the U.S. The rate now hovers about the replacement level
planning tool
Planning Tool
  • Population profile provides a means of planning for future demands on goods and services
  • Social Security
    • Will become big issue as baby boomer generation retires
future populations
Future populations
  • Current population growth is calculated from three vital statistics
    • Births
    • Deaths
    • Migration
  • 2005 statistics – U.S.
    • 4.18 million births, 2.44 million deaths, 946 thousand immigrants
      • 35% increase was due to migration
      • 65% due to natural increase
future populations1
Future Populations
  • Demographers can only make projections
    • Assumptions about fertility, mortality, and migration
projections for developing countries
Projections for Developing Countries
  • Ex – Italy
  • Population “graying”
    • Indicates that the proportion of elderly is increasing
  • Negative implications for business and industry

Note the large population of ages 30-49


Note how the larger numbers of persons are moving into older age groups and the number of children is decreasing

population projections for the u s
Population Projections for the U.S.

Projections shift drastically with changes in fertility. Contrast the 1988 projection based on a fertility rate of 1.8, with 2000 projection based on an increased fertility rate of 2.0 and current immigration

population projections for developing countries
Population Projections for Developing Countries
  • Fertility rates are dropping, but they are still well above replacement level
  • Average TFR (excluding China – 1.6) is 3.4
iraq s population in 2005
Iraq’s population in 2005

TFR = 4.8. Assuming that this fertility rate will gradually decline to 2.7 in 2025,t he population will increase from 29 to 40 million

ideal population structure
“Ideal” Population Structure
  • Equal numbers of persons in each age group, and a life expectancy of 75 years
population momentum
Population Momentum
  • Refers to the effect of current age structures on future populations
    • Iraq – positive population momentum
      • Small portion of the population is in the upper age groups and many children are entering their reproductive years
    • Europe – negative population momentum
      • Consequence of low fertility rate
      • Prompted several countries (e.g. France) to adopt a pro-natal policy
demographic transition
Demographic Transition
  • Basic premise is that there is a link between modernization and a decline in birth and death rates
birth rates death rate
Birth Rates/Death Rate
  • Crude Birth Rate (CBR)
    • Number of Births per 1,000 of the population per year
  • Crude Death Rate (CDR)
    • Number of Deaths per 1,000 of the population per year
  • Subtracting the DCR from the CBR gives you the increase (or decrease) per thousand per year
    • Dividing this number by 10 gives you the percent increase or decrease of the population
growth rate
Growth Rate

b/1000 – d/1000 = natural rate of increase

Natural rate of increase / 10 = % increase

A zero growth population is achieved if, the CBR and CDR are equal

doubling time
Doubling Time
  • Number of years it will take a population growing at a constant percentage per year to double
  • Calculated by dividing the growth rate into 70
epidemiologic transition
Epidemiologic Transition
  • Reminder: Epidemiologyis the study of factors affecting the health and illness of populations
  • Throughout most of human history, crude death rates were high
    • 40+/1000
  • By middle of the 19th century, epidemics and other social conditions were responsible for high death rates began to recede
epidemiologic transition1
Epidemiologic Transition
  • Developing countries CDR is at about 10/1000
  • Cancer, cardiovascular disease, and other degenerative diseases account for the majority of the mortality
  • Pattern of change in mortality factors is referred to as the epidemiologic transition
fertility transition
Fertility Transition
  • Now developed countries, birthrates have declined from 40 – 50 /1000 to 9-12/1000.
phase i
Phase I
  • Demographic transition
    • Primitive stability
    • Results from both death rates and birth rates being high
    • Small population size
phase ii
Phase II
  • Demographic Transition
    • Declining in CDR (epidemiological transition)
    • CBR still stays high
    • Population growth accelerates
phase iii
Phase III
  • Demographic Transition
    • Declining CBR – (fertility transition)
    • Population growth still remains high, but begins to slow down
phase iv
Phase IV
  • Demographic Transition
    • CBR = CDR, or CBR < CDR