Understanding:
• 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
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
