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.