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.

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’ work shows that the increase in quantity (population) is related to its size.
His observations of population growth trends indicated imminent resource depletion.

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.

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.

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) 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).

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.

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%.

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.

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.

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