Population Ecology

• 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 the 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.
• Exponential growth can be seen in populations that are very small or in regions that are newly colonised by a species.
• Exponential growth does not happen in natural populations for very long because the resources get used up. Population growth slows down when food and space become more difficult to find.

• 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 K).
• Logistic growth will eventually be seen in any stable population occupying a fixed geographic space.

Carrying capacity is dynamic – it can alter as a result of changes in either abiotic or biotic factors. The carrying capacity can also be lowered (reduced K) by resource destruction and degradation during an overshoot period. Example : Drought

Water becomes the limiting factor for kangaroos. Therefore the carrying capacity of the population is decreased, because the number of individuals that the current environment can support has been decreased.