Population Ecology Chapter 15 Review

Human World Population

• Current Population (2023): 7.9 billion people
  • More than double the population since 1965.
• Projected Population (2050): Approximately 9.8 billion people.
• Key Questions:
  • Can our planet support that many people?
  • Would everyone have the same level of support?

Population Growth Dynamics

• Growth Rate:
  • Defined as the difference between the birth rate and death rate.
  • Growth Rate = Birth Rate - Death Rate
  • Major determinants of population size include availability of resources, competition, and interactions with other species.

Exponential vs. Logistic Growth

• Exponential Growth: Occurs when populations are not limited by resources and can grow rapidly until they reach their carrying capacity.
• Logistic Growth: Growth is limited by environmental resources, stabilizing when reaching the carrying capacity (K).

Limits to Population Growth

• Carrying Capacity (K): Maximum population size that can be indefinitely supported by an environment. Factors that affect carrying capacity include:
  • Resources: Food, water, shelter, space.
  • Density-Dependent Factors: Factors such as limited food supply, higher disease risk that limit growth based on population density.
  • Density-Independent Factors: Environmental factors like natural disasters that affect populations regardless of their size.

Human Population Growth Trends

• Historical Growth: 1800: 1 billion; 1930: 2 billion; 1970: 4 billion; Current: 7.9 billion.
• Current Growth Rate: Approximately 1.2% per year, with 86 million people added annually.
• Demographic Transition: A shift characterized by initial high birth and death rates followed by declining death rates and eventually lower birth rates.

Resources and Energy Consumption

• Net Primary Productivity (NPP): The amount of vegetable matter produced in a given time. Essential for supporting human food needs.
  • The maximum NPP could theoretically support around 21 billion people, suggesting current food production is adequate for more than the current population.
• Energy Resources: Heavy reliance on non-renewable resources like fossil fuels.
  • Average American consumes significantly more resources compared to individuals in other countries, leading to higher strain on global resources.

Population Dispersion

• Types of Population Dispersion:
  • Clumped Distribution: High density in resource-rich areas (common in humans and many animal species).
  • Uniform Distribution: Individuals spaced equally (e.g., territorial species).
  • Random Distribution: No specific pattern, often seen in species that can tolerate a variety of conditions.

Measuring Population Size

• Methods:
  • Direct Census: Counting individuals directly.
  • Mark-Recapture Method: Involves capturing, marking, and then recapturing individuals to estimate population size.

Current and Future Projections

• Ongoing discussions on carrying capacity highlight the need for sustainable practices to manage population growth and resource utilization effectively.

Key Takeaways

• Despite current growth rates, human populations are not yet near carrying capacity based on resource availability, but trends suggest a need for management of resources and population dynamics to ensure sustainability.