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

2. What is a Population?
All members of a species living and reproducing together in the same place at the same time.
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?
Size
Density
Dispersal
Knowing the size, density, & dispersal of populations can help
characterize populations
predict changes within them
The
Map of population density of indigo bunting bird

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

5. What are the 3 properties of a population?
Density- the number of species per unit area or volume
Ex: number of bass per m3 of water in a lake
Usually body size affects density:
The larger the body size, the lower the population density.
The smaller the body size, the higher the population density.
In the graph a vertebrate poikilotherm is a cold-blooded animal whose body temperature is affected by the external environment.

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

7. 3 Types of Dispersal Patterns
Even
Evenly spaced
Not common type of dispersal
Ex: creosote bushes in desert
Random
Unpredictable spacing
Most rare type of dispersal
Ex: oyster larvae, dandelion seeds
Clumped
Live in groups
Most common type b/c resources are also clumped
Ex: school of fish, herd of zebra
Picture 1: Creosote bushes release a chemical called terpene thru their roots that keep other plants from invading their space and stealing their nutrients. This puts other creosote bushes at an even distance from them.
Picture 2: Dandelion seeds randomly float on the wind, land and germinate
Picture 3: Herd animals like zebra live in clumps because resources may be clumped as well (water is not evenly distributed across the land)

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

10. What is a Population’s Growth Rate (PGR)?
Change in a population over a given period of time.
Equation for PGR:
How to use the equation:
First calculate change in population
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
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:
Change in population = 13, ,481= 1,459
Population before change = 12,481
1459/12481 = x 100 = 11.7%
+11.7%

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

12. How fast can a population grow?
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.
Ex: Rabbits
Start breeding at 6 months and live for 7-10 years
Produce 6-14 babies in one litter
Gestation is 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.
Pictures represent the rabbit overpopulation that occurred in Australia back in the 1850’s. Rabbits were released, able to reproduce all year due to mild winters, overpopulated and destroyed crops. The myxomatosis virus was introduced to the rabbit population and it greatly reduced the population.

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

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

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

16. What limits exponential growth?
Populations will reach a carrying capacity- maximum population of a particular species that the ecosystem can support indefinitely
Represented by a straight line on a graph
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?
As population approaches its carrying capacity, there is competition for resources.
Organisms will compete indirectly for social dominance or for a territory to claim resources.

18. What are 2 types of population regulation?
Density Dependent limiting factors
Affected by crowded populations
Ex: food, water, disease
Plague spread faster thru cities than the country.
Density Independent limiting factors
Population size doesn’t matter, all will be affected equally
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?
Mark & Recapture
Species caught, tagged, released, then caught again. Proportion of marked to unmarked gives estimate
Used for animals mostly

20. How do scientists estimate population size in the field?
Mark & Recapture Equation
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?
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
N= mn = 10 x 15 = 30 turtles in this lake (approximate) r