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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