BS

Chapter 6 - Populations

Population Ecology

  • Studies the dynamics of species’ populations and how these populations interact with the environment.
  • Biotic Potential
    • Maximum reproductive capacity of an organism under optimum environmental conditions.
    • Often expressed as a percentage.
  • Carrying Capacity
    • Refers to the number of individuals that can be supported in a given area sustainably.
  • J-Curve
    • In a new environment, the population density of an organism increases rapidly in an exponential or logarithmic form, but then stops abruptly as environmental resistance or some other factor becomes effective.
  • S-Curve
    • Occurs when in a new environment, the population density of an organism increases slowly at first, then increases rapidly, reaching an exponential growth rate like the J-Curve, but then slows down to zero when the population stabilizes.
  • Reproductive Strategies
    • Organisms have adapted to maximize growth rates in environments that lack limits or to maintain population size.

Survivorship

  • Survivorship curves show age distribution characteristics of species, reproductive strategies, and life history.
  • Reproductive success is measured by how organisms are able to grow up and reproduce.
  • Type I Survivorship Curve - Reproduction happens early in life.
    • Low mortality at birth. Death rates increase with age.
  • Type II Survivorship Curve
    • Individuals at all age categories have uniform death rates.
  • Type III Survivorship Curve
    • Great numbers of offspring and reproduce for most of their lifetime.

Human Population Dynamics

  • Many different factors affect the human population.
  • Historical Population Sizes
    • The rapid growth of population in the world over the past 100 years has been due to the decrease in death rates.
    • The Human Population has had 3 surges of growth.
  • Distribution
    • In 1800, the majority of the world population was in Europe and Asia.
    • By 1900, 25% of the world population lived in Europe during the Industrial Revolution.
    • Now, most growth occurs in developing countries in Africa, Asia, Latin America.
  • Growth Rates and Doubling Times
    • The 20th century showed the biggest growth in world population in human history.

Demographic Transition

  • The processes that have occurred during the past century.
  • Stage 1 - Pre-Industrial
    • Living conditions are severe.
    • Medical care is poor or nonexistent.
    • Food supply is limited.
    • Birth rates are higher due to high mortality rates.
    • Little population growth.
  • Stage 2 - Transitional
    • Occurs after the start of industrialization.
    • Medical care advances, sanitation is improved.
    • Cleaner water supplies, vaccinations, higher levels of education make death rates lower.
  • Stage 3 - Industrial
    • Urbanization decreases the economic incentives for large families.
    • Parents are discouraged from having large families due to cost.
    • Decreased birth rates due to jobs for women.
  • Stage 4 - Post-Industrial
    • Birth rates equal mortality rates.
    • Birth rates and mortality rates are low.
    • There is no population growth.
  • Strategies for Population Sustainability
    • Provide economic incentives for having fewer children
    • Provide free education, housing subsidies, monthly subsidies, free healthcare, higher pension benefits, tax incentives, or other economic incentives for women with one or two children.
    • Provide more job and employment opportunities to women.
    • Provide government family-planning services.
    • Increase economic development in developing countries.
    • Improve prenatal and infant health care.

Impacts of Population Growth

  • Biodiversity - Earth’s biological diversity is crucial to the continued vitality of agriculture and medicine. Human activity is bringing organisms to extinction throughout the word.
  • Coastline and Oceans - Ocean fisheries are being exploited.
  • Forests - Half of the world’s original forests have been lost. Forests provide $400 Billion a year and are vital to maintaining healthy ecosystems.
  • Food Supply and Malnutrition - ¼ of the world today is malnutrition. The issue is the world cannot produce enough food.
  • Freshwater - Demand for freshwater is soaring as the population grows.
  • Global Climate Change - Earth’s surface is warming due to greenhouse gases, largely from burning fossil fuels.
  • Public Health and Increase in Disease - Unclean water kills 12 million people yearly. Air pollution kills 3 million yearly.
  • Unequal Distribution of wealth and governmental priorities - Rapid population growth can make it politically difficult for countries to raise standard of living.