Population Ecology
Biology 1-2
Population Ecology

Population ecology studies changes in
population size and the factors control their
size over time.

Population-a group of individuals of the same
species in a defined area.
Population Growth

The size of a population is based on two sets of
opposing factors.

Growth factors-factors that cause a population to
grow.


Lots of food or living space, good climate, little
competition or predation.
Limiting factors-factors that cause a population to
shrink.

Little food or living space, poor climate, lots of
competition/predation, disease.
Exponential Growth

If given unlimited space
and resources, a
population can grow
exponentially.

No environment can
support exponential
growth forever.

Resources are limited.
Carrying Capacity

Growth and limiting factors work against each
other to create an upper limit to a population.

Carrying capacity-maximum number of
individuals an area can support indefinitely.
Carrying Capacity cont’d

Growth factors cause
the population to
increase.


Limiting factors slow the
growth rate.
At the carrying capacity,
the growth rate is zero.
Life Histories

The life history of an organism is all the
events from birth to death. Includes:




When it reproduces.
How often it reproduces.
Number of offspring.
Amount of care.
Life Histories cont’d

Organisms can be put into two groups, based
on their life histories.


r-selected species
K-selected species
r-Selected Species

r-selected species use most of their energy for
their offspring.




Produce lots of offspring.
Provide little or no care for the young.
Tend to be smaller and shorter lived organisms.
Have low survival rates.


If they make it past infancy they live to an old age.
Allows them to succeed in unstable environments.
r-Selected Species cont’d

r-selected populations reproduce rapidly and
easily overshoot the carrying capacity.


They grow rapidly and use up resources.
Limiting factors increase and their numbers drop
off.


When the population is low enough they recover.


Too many predators, not enough food.
Less predation, more food.
Swing back and forth around the carrying capacity.
K-Selected Species

K-selected species are organisms that put their
energy into raising their young.




Have fewer offspring.
Provide lots of care for the young.
Higher infant survival rates.
Tend to be larger and longer lived.
K-Selected Species cont’d

K-selected populations grow much more
slowly.



Level off as they near the carrying capacity.
Reproduce so slowly they cannot handle change
very well.
Work to ensure the survival of their young.