AC

Recording-2025-01-17T16:01:32.896Z

Human Population Growth

  • From 1900 onwards, human population has increased rapidly, overshadowing deaths from diseases, wars, etc.

  • This phenomenon is termed exponential growth, a model used by ecologists.

Exponential Growth Explained

  • Key concept: Growth rate is constant; population changes depend proportionally on current size.

  • Thomas Malthus (1798) predicted that human populations would eventually surpass resources, leading to famine and disease.

Malthus’ Prediction

  • Malthus’ work shows that the increase in quantity (population) is related to its size.

  • His observations of population growth trends indicated imminent resource depletion.

Exponential Growth Graph

  • The graph showing proportional increase of population size over time is J-shaped.

  • Analogy: Money in a bank earns interest; larger deposits yield more interest, similar to populations increasing in size and speed.

Population Change Factors

  • Factors affecting population growth:

    • Birth rates: Represents the number of births contributing to the population increase.

    • Immigration: Movement of individuals into a population.

    • Death rates: Represents mortality, contributing to the population decrease.

    • Emigration: Movement of individuals out of a population.

  • Expressed in the equation for population change:

    • Population Change (N) = Births + Immigration - Deaths - Emigration.

Mathematical Expressions of Population Growth

Change in Population Size

  • For discrete changes:

    • Change in population size = Nₜ₊₁ - Nₜ

  • For continuous changes, using calculus:

    • dN/dT (change in population size over time).

Growth Rate (r)

  • Growth rate (r) is critical for understanding population dynamics.

  • High r indicates rapid population growth, while low or negative r suggests decline.

  • Population size and growth rate dictate whether the population grows (+), declines (-), or remains stable (0).

Example: Gerbils and Turtles

  • Calculating r using:

    • Gerbils: Start with 10, end with 12, r = (12-10)/10 = 0.2 or 20%.

    • Turtles: Start with 10, end with 8, r = (8-10)/10 = -0.2 or -20%.

  • Demonstrates differing population trajectories based on r values.

Human Population Dynamics

Theoretical Perspectives

  • Theoretical maximum growth (r) for humans could be as high as 11% per year, but current growth is about 1.8%.

  • The historical growth rate was much lower (0.2%) prior to the 20th century.

  • To achieve zero population growth, r must fall below 0.1%.

Real World Observations

  • Post-1900, global death rates declined due to advances in hygiene, healthcare, and nutrition.

  • The result was a surge in population size despite a steady birth rate.

Key Takeaways

  • Exponential growth is characterized by:

    • A constant growth rate, r, affecting the population's trajectory.

    • Changes in population dynamics due to birth and death rates, influenced by medical, social, and environmental factors.

  • Understanding how these components interact is crucial for examining human impacts on ecosystems.

Conclusion

  • Future discussions will delve deeper into the implications of these growth patterns and potential limiting factors affecting populations.