Factors that Influence Population Size

Size

Density

Distribution

Immigration

Emigration

decrease population size

increase population size

number of individuals in a given area

location of individuals relative to one another

Limits on Population Growth

Density-Dependent Factors

Density-Independent Factors

causes birth rate to slow and death rates to rise

predation, parasitism, disease, and competition

Logistic growth

occurs when density-dependent factors affect population size over time

natural disasters or weather-related events affect population size

K selection

occurs when a population is near its environment's carrying capacity

R selection

occurs when population density is low and resources are abundant

arrival of new residents that previously belonged to another population

the departure of individuals who take up permanent residence elsewhere