Download Unit 3A Ch 8 S1- How Populations Change in Size

Understanding
Populations
Ch8, Section 1: How Populations Change
in Size
Standards: SEV3e
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.
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
What are the 3 properties of a
population?
1. Size- the
number of
species
present
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.
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
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
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
What is a Population’s
Growth Rate (PGR)?
Change in a population over a given
period of time.
O Equation for PGR:
O
O
How to use the equation:
First calculate change in population
1.
O
2.
3.
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
If answer is negative the population
declined
O If the answer is 0 the population did not
change.
O
O
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%
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)
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.
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
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)
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 S-shaped
curve on the graph. This
is called logistic growth.
What limits exponential
growth?
O Populations will reach a
carrying capacity- maximum
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.
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.
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
How do scientists estimate
population size in the field?
O Mark & Recapture
O Species caught,
tagged, released,
then caught
again. Proportion
of marked to
unmarked gives
estimate
O Used for animals
mostly
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
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