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.

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