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.