Chapter 5 How Populations Grow

Characteristics of Populations  Population density  The number of individuals per unit area.  Varies depending on the species and its ecosystem.

Population Growth  3 factors that affect population size  The number of births  The number of deaths  The number of individuals that enter or leave the population.

Population Growth  A population can grow IF:  The number of births is higher than the number of deaths.  More individuals move into the population than out of it. (Immigration)

Population Growth  A population will stay the same size IF:  There are the same number of births as deaths.  The same number of individuals move into the population as move out of the population.

Population Growth  A population will decrease in size IF:  There are more deaths than births  More individuals move out of the population than into it. (Emigration)

Immigration vs. Emigration  Immigration is the movement of individuals into a population.  Immigration = In  Emmigration = Exit

Exponential Growth  When the individuals in a population reproduce at a constant rate.  * Under ideal conditions, a population will grow exponentially.

Exponential Growth of an Elephant Population

Logistic Growth  Occurs when a populations growth slows or stops following a period of exponential growth.  Usually caused by a population reaching carrying capacity.

Logistic Growth