Definition:

"A population is a group of organisms of the same species living in the same area at the same time, and which are capable of interbreeding"

Population growth

Shows increase in the number of individual of a species over time

This increment can either be…

• Exponential or

• Limited by carrying capacity

Each species has a strategy to maintain the growth over many generations

• r – strategist

• K – strategist

Factors affecting growth:

• Density-dependent factors operate as negative feedback mechanisms regulating the population and leading to stability. 

  • Predator–prey relationships are a good example of density-dependent control.

• Density-independent factors are generally abiotic. The most important ones are extremes of weather (drought, fire, hurricanes) and long-term climate change. Others include geophysical and geological events such as earthquakes and volcanic eruptions and the tsunamis that can result from them. Their impacts include an increase in the death rate and a reduction in the birth rate, especially of smaller individuals.

  • The response depends, in part, on the frequency and severity of the event. Density-independent factors can operate alongside density-dependent factors.

  • Density-independent factors may have significant influence on population size, but it is the density-dependent factors that tend to regulate the population around the carrying capacity. In addition to competition for limited resources, these factors include the increased risk of predation and the transfer of pathogens in dense populations

Limiting factors slow population growth as it approaches the carrying capacity of the system.

Limiting factors for…:

• for plants:   light, nutrients, water, CO2 and temperature

• for animals:  space, food, mates, nesting sites and water

• Populations have an upper level or extent to the number of individuals that can be sustained in each environment.

• Carrying capacity is the term used to describe the maximum number of individuals of a species that can be sustained by an environment.

• The carrying capacity represents the population size at which environmental limiting factors limit further population growth.

• The carrying capacity of a population is affected by various limiting factors, such as:

  • the availability of food and water

  • territorial space

  • Predation

  • Disease

  • availability of mates

•A characteristic that is often quantified with population numbers, interactions between organisms and their biotic and abiotic factors can be studied

•Generally, there are only two possible responses population numbers can have, to changes in the conditions (biotic and abiotic factors):