How Populations Grow

What is a Population?

• A population consists of all individuals of a species that live together in one place at one time.

Three Key Features of Populations

• Population size is the number of individuals in a population.

• Population density is the number of individuals that live in a given area.

• Dispersion is the way the individuals of a species are arranged in space.

Modeling Population Growth

• A population model is a hypothetical population that attempts to exhibit the key characteristics of a real population.

• Exponential growth curve is a curve in which the rate of population stays the same as a result the population growth stays the same, as a result the population size increases steadily.

Exponential Growth Curve

Modeling Population Growth

• Carrying capacity is the population size that an environment can sustain.

• Density-dependent factors is when limited resources are affected by the density of the population that uses them.

• Logistic model is a population in which the exponential growth is limited by a density-dependent factor.

Logistic Growth Curve

Population Growth Models

• Calculating the population growth rate –

• r (rate of growth) = birthrate – death rate

• Exponential growth rate –

• Logistic model -

Growth Patterns in Real Populations

• Density-independent factors – growth is limited by environmental conditions. (weather and climate)

• r-strategies – species found in rapidly changing environments.

• K-strategies – species that grow slowly and have small population sizes.