Populations - Chapter 19

Characteristics of Populations Three important characteristics of a population are: Geographic Distribution Density Growth Rate Also: Age Structure of the Population

Three factors can affect population size: Population Dynamics Three factors can affect population size: Number of Births Number of Deaths Life expectancy Age structure

Population Growth Rate Definition: the amount by which a population‘s size changes in a given time. Birth rate – death rate = growth rate.

Immigration – the movement of individuals into an area/population Emigration - the movement of individuals out of an area/population

Exponential Growth Under ideal conditions, a population will continue to grow in a pattern called exponential growth. Exponential Growth occurs when individuals in a population reproduce at a constant rate.

Exponential Growth

Logistic Growth As resources become less available, the growth of a population slows or stops. Logistic Growth occurs when a population’s growth slows or stops following a period of exponential growth.

Carrying Capacity The point at which the average growth rate reaches zero. It is the largest number of individuals that a given environment can support

Logistic Growth and Carrying Capacity

Limits to Growth Limiting Factors Factors that cause population growth to decrease

Density-Dependent Limiting Factors A limiting factor that depends on population size Includes: Competition Predation Parasitism Disease

Parasitism Climate Competition Predation Human Disturbances

Density-Dependent Limiting Factors

Density-Independent Limiting Factors Affect all populations in similar ways, regardless of the population size. Includes: Unusual Weather Natural Disaster Seasonal Cycles Human Activities

Human Population Growth The size of the human population tends to increase with time. The scientific study of human populations is called demographics.

Human Population Growth

These factors can be shown in an age-structure diagram. Some factors that help predict why some countries have high growth rates while other countries grow more slowly are: Birthrates Death rates Age Structure These factors can be shown in an age-structure diagram.

Age Structure Diagrams