KEY CONCEPT Populations grow in predictable patterns.

Changes in a population’s size are determined by immigration, births, emigration, and deaths. The size of a population is always changing. Four factors affect the size of a population. Immigration – the movement of individuals into one population from another. Births – increase the number of individuals in a population. Emigration – the movement of individuals out of a population and into another population. Deaths – decrease the number of individuals in a population.

Population growth is based on available resources. Exponential growth is a rapid population increase due to an abundance of resources. Fig. In Australia during the early 1900s, the introduced European rabbit population exhibited exponential growth. Formula for calculating exponential growth: y=abx y= population # a= # of females x= # of years (generations) b= # of offspring/female

Logistic growth is due to a population facing limited resources.

Carrying capacity is the maximum number of individuals in a population that the environment can support. A population crash is a dramatic decline in the size of a population over a short period of time.

Ecological factors limit population growth. A limiting factor is something that keeps the size of a population down. Density-dependent limiting factors are affected by the number of individuals in a given area. Fig. Taking down prey as large as a moose requires that the members of a pack work together. As many as ten wolves may take hours or even days to wear down this moose.

Density-dependent limiting factors are affected by the number of individuals in a given area. predation competition parasitism and disease

Density-independent limiting factors limit a population’s growth regardless of the density. unusual weather natural disasters human activities Fig. The storm surge accompanying a hurricane can cause dangerous flooding.