5.1 How Populations Grow

Researchers study populations' geographic range, density and distribution, growth rate, and age structure.

The factors that can affect population size are the birthrate, the death rate, and the rate at which individuals enter or leave the population.

Under ideal conditions with unlimited resources, a population will grow exponentially.

Logistic growth occurs when a population's growth slows and then stops, following a period of exponential growth.

• population density (131)

• exponential growth (132)

• age structure (131)

• logistic growth (135)

• immigration (132)

• carrying capacity (135)

• emigration (132)

5.2 Limits to Growth

Acting separately or together, limiting factors determine the carrying capacity of an environment for a species.

Density-dependent limiting factors operate strongly when population density reaches a certain level. Density-dependent limiting factors include competition, predation, herbivory, parasitism, disease, and stress from overcrowding.

Density-independent limiting factors affect all populations in similar ways, regardless of population size and density. Unusual weather such as hurricanes, droughts, or floods, and natural disasters such as wildfires, can act as density-independent limiting factors.

• limiting factor (137)

• density-dependent limiting factor (138)

• density-independent limiting factor (140)

5.3 Human Population Growth

The human population, like populations of other organisms, tends to increase. The rate of that increase has changed dramatically over time.

Birthrates, death rates, and the age structure of a population help predict why some countries have high growth rates while other countries grow more slowly.

• demography (143)

• demographic transition (144)

Think Visually Create a table in which you describe the phases of logistic growth.