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Population. Chapter 5: Pages 108-115 Chapter 6: Pages 123-137. Population Characteristics. Population dynamics – study of how distribution numbers, age structure and density of populations change in response to changes in environmental conditions.

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Chapter 5: Pages 108-115

Chapter 6: Pages 123-137

Population characteristics
Population Characteristics

Population dynamics – study of how distribution numbers, age structure and density of populations change in response to changes in environmental conditions.

Most populations live in clumps, uniform dispersion or random dispersion.

Population changes
Population Changes

  • Four variables affect the size of a population:

    • Births

    • Deaths

    • Immigration

    • Emigration

      Populations with a large number in the “reproductive stage” is likely to increase.

Population growth
Population Growth

Intrinsic rate of increase (r) – the rate at which a population of a species would grow if it had unlimited resources.

Is r possible?

Smaller organisms have a greater capacity for growth (biotic potential).

Population growth1
Population Growth

  • Environmental resistance – factors that limit growth of a population.

  • Carrying capacity – the maximum population of a given species that a particular habitat can sustain indefinately without being degraded.

    • Determined by biotic potential and environmental resistance.

Population crash
Population Crash

  • Populations can crash when they exceed the carrying capacity of their environment.

    • Sometimes this can decrease the carrying capacity of an environment.

Reproductive patterns
Reproductive patterns

R-selected species – capacity for a high rate of population increase. Usually have many small offspring and give little care. (opportunists)

K-selected species – reproduce later in life and have a small number of offspring with fairly long life spans (competitors)

Genetic diversity
Genetic Diversity

Founder effect – a few members colonize and isolated area.

Demographic bottle neck – only a few individuals of a population survive a catastrophe.

Genetic drift – random changes in gene frequencies due to unequal reproductive success.

Inbreeding – individuals in a small population breed with one another.

All decrease genetic diversity and decrease chances of survival.

Types of population change
Types of Population Change

Stable, irruptive, cyclic and irregular.

Human population growth
Human Population Growth

Three major factors account for human population increase: 1. ability to expand into diverse new habitats. 2. modern agriculture

3. sanitation, antibiotics, vaccines

225,000 people are added to earth’s population each day.

Cultural carrying capacity – most people living in reasonable comfort without impairing the ability of the earth to sustain future generations.

Population size factors
Population Size Factors

  • Population change = (births + immigration) – (deaths + emigration)

  • Birth rate – number of births per 1000 people

  • Death rate – number of deaths per 1000 people

Population size factors1
Population Size Factors

  • Fertility rate – number of children born to a woman in her lifetime.

    • Replacement fertility rate – average number of children that couples in a population must bear to replace themselves. (2.1 – 2.5)

    • Total fertility rate – average number of children born to a woman during her reproductive years. (key to determining population size)

Population size factors2
Population Size Factors

Birth and fertility rates are affected by: 1. importance of children in the labor force

2. cost of raising and educating children

3. availability of pension systems

4. urbanization

5. educational and employment opportunities for women

6. infant mortality rate – number of children per 1000 births that die before one year of age.

7. Average age at marriage

8. availability of legal abortions

9. availability of birth control

10. religious beliefs, traditions and cultural norms

Population size factors3
Population Size Factors

  • Death rates are affected by:

    1. life expectancy – average number of years a newborn infant can expect to live.

    2. infant mortality rate

    3. food supplies and distribution

    4. better nutrition

    5. medicine

    6. sanitation

    Why does the U.S have a higher infant mortality rate (6.6) than other developed countries?

Population age structure
Population Age Structure

Age structure – the distribution of males and females among age groups in a population.

Age structure diagrams can be used to make population and economic projections.

Slowing population growth
Slowing Population Growth

Demographic transition – as countries become industrialized, first their death rates and then their birth rates decline. (4 stages)

Family planning – providing educational and clinical services so couples can choose how many children they have.

Empowering women – women have fewer children if they are educated, hold a paying job outside the home, and live in societies where their human rights are not suppressed.

Globally women account for 2/3rds of the hours worked and receive only 10% of the worlds income.