1. Understanding
Populations
Ch8, Section 1: How Populations
Change in Size
Standards: SEV3e

2. What is a Population?
O All members of a
species living and
reproducing together
in the same place at
the same time.
O A population of
daisies in a field in
Georgia would only
reproduce together.
They would not
reproduce with a field
of daisies in Alabama.

3. What are the 3 properties of a
population?
1.
2.
3.
Size
Density
Dispersal
Knowing the
size, density, &
dispersal of populations
can help
O characterize
populations
O predict changes
within them
Map of population density
of indigo bunting bird

4. What are the 3 properties of a
population?
1. Size- the
number of
species
present

5. What are the 3 properties of a
population?
2.
Density- the
number of species
per unit area or
volume
O Ex: number of bass
per m3 of water in a
lake
O Usually body size
affects density:
O The larger the body
size, the lower the
population density.
O The smaller the
body size, the
higher the
population density.

6. What are the 3 properties of a
population?
3. Dispersal- relative
distribution or
arrangement of
individuals in a
particular space.
O 3 Types:
a.
b.
c.
Even
Random
Clumped

7. 3 Types of Dispersal Patterns
a.
Even
O
O
O
b.
Random
O
O
O
c.
Evenly spaced
Not common type of
dispersal
Ex: creosote bushes in
desert
Unpredictable spacing
Most rare type of dispersal
Ex: oyster larvae, dandelion
seeds
Clumped
O
O
O
Live in groups
Most common type b/c
resources are also clumped
Ex: school of fish, herd of
zebra

9. How does a population grow?
O Organisms enter a
population via birth.
O Organisms leave a
population via death
O Natural change in
population size =
births - deaths

10. What is a Population’s
Growth Rate (PGR)?
O
Change in a population over a given
period of time.
O Equation for PGR:
O
How to use the equation:
First calculate change in
population
1.
O
2.
3.
O
New pop. Size – Old pop. size
Next divide change in population
by the original population size
Multiply answer x 100 to get %
If answer is positive the population
grew
O If answer is negative the population
declined
O If the answer is 0 the population did
not change.
In the year 2000, the population
of Powder Springs was 12,481.
In the year 2010, the population
of Powder Springs was 13,940.
How much did the population
grow during this 10 year period?
Use the Population Growth Rate
equation to figure this out!
Answer:
+11.7%

11. How fast can a population
grow?
O Reproductive potential-
maximum number of offspring
that each member of the
population can produce.
O Usually the smaller the
animal, the higher the
reproductive potential.
O Ex: insects, rodents, bacteria
O Affected by:
O How often organism
reproduces in their lifetime
O How early in life they start
reproducing
O How many offspring they
produce in a single
reproductive cycle (pregnancy)

12. How fast can a population
grow?
O If an organism reproduces when it
is young, has a lot of babies in
one cycle, and can have many
cycles in its life then it has a HIGH
reproductive potential.
O Ex: Rabbits
O
O
O
O
O
Start breeding at 6 months and live
for 7-10 years
Produce 6-14 babies in one litter
Gestation is 14-31 days so can
have 1 litter per month.
An 8 year old rabbit could produce
1,344 babies in her life. AND if she
gives birth to females they will also
have babies.
RabbitHealth.com predicts 1 rabbit
can be the progenitor of 95 million
rabbits if you include all the female
babies and their births.

13. What is exponential growth?
O Population multiplies
at fast increasing rate
O Results from lack of
limiting factors
O If there’s plenty of
food, water, shelter
then unlimited
number of
organisms can
survive.
O Produces J-shaped
curve on graph

14. What limits exponential
growth?
O Limited resources keep
populations from reaching
their reproductive potential
and experiencing
exponential growth.
O Examples of limiting
factors:
O Food
O Water
O Shelter
O Availability of mates
O Availability of light (plants)

15. What limits exponential
growth?
O Limiting factors cause
some animals to die and
birth rates to decrease.
O Populations will rise and
fall around a particular
population size.
O This population
oscillation creates an Sshaped curve on the
graph. This is called
logistic growth.

16. What limits exponential
growth?
O Populations will reach a
carrying capacitymaximum population of a
particular species that the
ecosystem can support
indefinitely
O Represented by a straight
line on a graph
O The population of a
species will oscillate
around the carrying
capacity.
What is the carrying capacity for
this population?
Approximately 1.5 million
organisms.

17. What limits exponential
growth?
O As population
approaches its
carrying
capacity, there is
competition for
resources.
O Organisms will
compete indirectly
for social
dominance or for a
territory to claim
resources.

18. What are 2 types of population
regulation?
O Density Dependent
limiting factors
O Affected by crowded
populations
O Ex: food, water, disease
O Plague spread faster
thru cities than the
country.
O Density Independent
limiting factors
O Population size doesn’t
matter, all will be affected
equally
O Ex: temperature
fluctuations, natural
disasters.
Density Independent
Example: Temperature has
caused decrease in
mosquito population

19. How do scientists estimate
population size in the field?
O Mark & Recapture
O Species
caught, tagged, r
eleased, then
caught again.
Proportion of
marked to
unmarked gives
estimate
O Used for animals
mostly

20. How do scientists estimate
population size in the field?
O Mark & Recapture Equation
O N= mn
r
Where…
N= estimate of population size
m= number of individuals caught on first visit
n= number of individuals caught on second visit
r= number of marked individuals caught on 2nd visit
Must assume that…
- Population is closed geographically & no immigration or
emigration
- All organisms are equally likely to be captured
- Catching & marking do not affect catchability
- Each sample is random
- Marks are not lost between sampling occasions

21. How do scientists estimate
population size in the field?
O A biologist wants to estimate the size of a population
of turtles in a lake. She captures 10 turtles on her first
visit to the lake, and marks their backs with paint. A
week later she returns to the lake and captures 15
turtles. Five of these 15 turtles have paint on their
backs, indicating that they are recaptured animals.
What is the estimated size of the population?
m = #originally marked = 10
n = total # caught in 2nd sample = 15
r = # caught in 2nd sample that were marked = 5
O N= mn = 10 x 15 = 30 turtles in this lake
(approximate)
r
5