Download Population Growth

5-1 and 5-2 Population Growth
Charles Darwin calculated that a single
pair of elephants could increase to a
population of 19 million individuals
within 750 years.
The fact that the world is not overrun
with elephants is evidence that some
factor or factors restrain the population
growth of elephants.
Characteristics of populations
A. 4 important characteristics
1. Density
2. Geographic distribution
3. Growth rate
4. Age Structure
2. Population density
A. Number of individuals per unit area.
B. Can vary tremendously depending on the
ecosystem and species.
1.
3. Population Growth
A. Growth rate is the amount by which
a population’s size changes in a given
time.
B. Growth depends on four processes:
1. Number of births
2. Immigration
3. Emigration
4. Number of deaths
C. Immigration is the movement of
individuals into an area
1. Causes the population size to
increase.
D. Emigration is the movement of
individuals out of an area
1. Causes the population to
decrease in size.
4. The Exponential Growth
A. The exponential growth
1. Organisms in a population reproduce at a
constant rate, and the larger the population the
faster it will grow.
2. As long as there are no restraints such as
predation, space, resources, diseases and
competition a population will grow
exponentially.
B. Limits to the Exponential Model
1. This happens for a short period of time
and under rare conditions.
2. Limiting factors: a factor that restrains
the growth of a population, like drought, scarce
resources, scarce space, diseases, predation
and competition.
3. End result: declining birth rate and an
increasing mortality rate.
5. The Logistic Growth
A. Logistic growth
1. Accounts for resources becoming less available,
which either slows or stops growth rate completely.
Usually occurs after exponential growth.
2. Carrying Capacity (K): the number of
individuals the environment can support
over a
long period of time.
Logistic Growth of fur seals
5:2

Limits to
Growth
1. Limiting Factors
A. Is a factor that causes population
growth to decrease.
B. Density Dependent Factors
1. Become limiting when the
population density reaches a certain
level.
2. Affect large, dense populations.
3. Include factors such as competition,
predation, parasitism, and disease.
Density Independent factors
1. Will affect all populations in
similarways, regardless of the
population size.
2.. Examples include: weather,
Natural disasters, seasonal cycles,
damming rivers and clear-cutting
forests.
C.
7.
Predator prey relationship
A. Population size is often regulated
by nature.
B. Ex. Lynx and Snowshoe hare
1. Each species keeps the others
population size in check, or under
control for the environment.
Snowshoe hare
and
Lynx
populations
(classic
example)