Population Growth

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•  The exponential growth pattern occurs in an ideal, unlimited environment

•  Population growth slows as the population reaches the carrying capacity of the environment

Two types of population growth patterns may occur depending on specific environmental conditions:

  • An exponential growth pattern (J curve) occurs in an ideal, unlimited environment
  • A logistic growth pattern (S curve) occurs when environmental pressures slow the rate of growth

Exponential Growth

  • Exponential population growth will occur in an ideal environment where resources are unlimited
  • In such an environment there will be no competition to place limits on a geometric rate of growth
  • Initially population growth will be slow as there is a shortage of reproducing individuals that may be widely dispersed
  • As population numbers increase the rate of growth similarly increases, resulting in an exponential (J-shaped) curve
  • This maximal growth rate for a given population is known as its biotic potential
  • Exponential growth can be seen in populations that are very small or in regions that are newly colonised by a species

Logistic Growth

  • Logistic population growth will occur when population numbers begin to approach a finite carrying capacity
  • The carrying capacity is the maximum number of a species that can be sustainably supported by the environment
  • As a population approaches the carrying capacity, environmental resistance occurs, slowing the rate of growth
  • This results in a sigmoidal (S-shaped) growth curve that plateaus at the carrying capacity (denoted by κ)
  • Logistic growth will eventually be seen in any stable population occupying a fixed geographic space

Types of Population Growth

population growth

Limiting Factors

Limiting factors are environmental conditions that control the rate at which a process (e.g. population growth) can occur

  • Population growth can be determined by density-dependent or density-independent factors

Density dependent environmental factors are influenced by the relative size of a population

  • These factors include predator numbers, availability of food and other resources and the spread of pathogenic diseases

Density independent environmental factors are not influenced by the relative size of a population

  • These factors include weather and climate conditions, as well as the occurrence of natural disasters (e.g. earthquakes)

Examples of Population Factors

selection pressures