Factors Affecting Population Change

A. Density-dependent factors limit population growth and intensify as the population increases in size (i.e. Competition for resources, disease...)

Density-dependent factors

1. Intraspecific competition is when individuals of the same species compete for resources. If this is high then the population will have a low growth rate.

Density-dependent factors

2. Predation is the consumption of prey by a predator. If there is more prey available they will be chosen more by predators.

Density-dependent factors

3. Allee effect: Warder Allee found that some density-dependent factors reduce population growth when the population is at a low density rather than high density.

Ex. harder for individuals to find a mate and successfully reproduce thus lowering the growth rate of species.

Allee-effect continued

Small populations also may go through inbreeding depression which reduces the populations' genetic variability and may prevent successful population growth.

Allee-effect continued

The minimum viable population size is the smallest number of individuals that ensures the population will persist for a certain period of time.

Allows biologists to determine whether a species is endangered.

Factors Affecting Population Change

B. Density-independent factors limit population growth no matter what the population size

i.e. Natural disaster, human intervention...

Density-independent factors

The resource in the ecosystem that is in the shortest supply is known as the limiting factor since it is preventing massive population growth.

Population Change Affects the Entire Ecosystem A change in one

population of species can affect the entire hierarchy of living things in that ecosystem. Ex. The disappearance

of beaver from this ecosystem causes a decrease in the wolf population which would cause an increase in its other prey