Population Growth and Dynamics

Calculating Change in Population

• Formula: Change in population = (Birth Rate x Population) - (Death Rate x Population)
• Birth Rate: Number of births per 1,000 individuals
• Death Rate: Number of deaths per 1,000 individuals
• Overall Rate (r): Birth Rate - Death Rate
  • Zero Population Growth (ZPG): Occurs when Birth Rate = Death Rate, resulting in 'r' being 0

Exponential Growth

• Idealized Conditions: Unlimited food, space, resources
• Characteristics:
  • Occurs when Birth Rate > Death Rate
  • Results in exponential (J-shaped) growth curve
  • Growth accelerates as population size increases
  • Example: Elephant population in Kruger National Park after hunting ban
• Limitation: Cannot be sustained indefinitely due to limited resources

Logistic Population Growth

• Carrying Capacity (K): Maximum population size sustainable due to limited resources
• Growth Model: Considers resource limits
  • Mathematical expression: Growth Rate x Population = K - Population / K
• Increasing Population:
  • When population < K, positive growth
  • Example: Population = 9,000, K = 10,000 results in growth
• Decreasing Population:
  • When population > K, negative growth

Factors Affecting Growth

• Impact of N relative to K:
  • Small N compared to K: Growth rate close to maximum
  • Large N compared to K: Growth rate decreases
• S-shaped Curve:
  • Sigmoid growth as population approaches K
  • Fastest growth at intermediate sizes

Experimental Observations

• Laboratory Studies:
  • Paramecia experiments show sigmoid growth curve
  • Overshooting K can occur temporarily

Allee Effect

• Definition: Difficulty in survival and reproduction with small population sizes
• Impact: Growth is hindered with too few individuals