1. SBI4U Population Dynamics
Characteristics of Populations

2. Study the picture of the wetland -

3. What is a Population?
Population: a group consisting of members of the same species that live together in a certain area at the same time
Populations live in a particular habitat, that provides them with the resources they need
Community: consists of all populations of all species that live and interact in the same area
Ecosystem: A community plus it’s abiotic environment
Population Dynamics: the study of changes in populations

4. Terminology
Brainstorm with your lab partner to define the following terms in your own words AND provide an example.
Population size (N)
The number of individuals of the same species living within a specific geographical area.
Population density (Dp)
Number of individuals of the same species that occur per unit of area or volume.
Think-Pair-Share

5. How many daisies in the field?
You have 15 seconds… 78

6. How many did you count? How did you estimate the number of daisies?
Did you try to count them all?
Or did you use another method?
We need a quantitative estimate for the number of daisies – it doesn’t have to be perfect but it should be as close as possible to the real number.
Write your first estimate down, then try again, seeing if this will help…

7. 78

8. Is your estimate the same?
How did you use the grid to estimate the number of daisies? Did it help?
There are 78 daisies
If you were asked to count the number of daisies in the school field, it would be impractical to count each one.
How could you use the grid method to get an accurate, reproducible estimate? Make a rough plan.
Use your plan to make an estimate for the next field:

9. 103

10. How many daisies were there?
There were 103 daisies in the field. How close were you?
Your plan should have involved the following steps:
Select at least three quadrats and count how many daisies are in each (eg 4, 8, 3)
Add them to get a total and divide by the number of samples to find the mean number of daisies per quadrat ( = /3 = 5 daisies per quadrat)
Multiply the mean by the number of quadrats that would fit into the field to get your estimated total number of daisies. (5 x 20 = 100 daisies estimated in the field)

11. Can you determine the population size?

12. Characteristics of Populations – Population Density
Who cares how big or dense a population is?
The density of a population can be related to how healthy the population is. We will talk about this and what influences population size/density in more detail later.....

13. measuring Population Size and Density
How do we determine the human population?
Can we use the same methods with other species? Why or why not?
Instead of counting individuals in a populations inefficiently, ecologists estimate population size by studying smaller samples  extrapolation
3 methods:
Transects
Quadrats
Mark-Recapture

14. Transects
Transect – a long line or narrow area used for population sampling
Researchers choose a line of specific length (i.e. 100m)
Walk along the line and count number of individuals of each species being monitored within the area
For sessile organisms – within 1m
Mobile organisms – within 50m
Example:

15. Transects Useful for: low population densities or
larger organisms like trees

16. Quadrats Quadrat – a box used to sample a population
Location is chosen at random
Quadrat is drawn  area can be large or small depending on size of species under study (A)
Number of individuals are counted within quadrat boundaries (N)

17. Quadrats
Information can be used to calculate population density:
DP = N/A
Sample Problem:
Ecologists are sampling the distribution of flowering white trillium plants in a section of forest covering 100m x 100m (so what is the area)?
They place four 1m by 1m quadrats randomly
They find 5, 4, 3, and 1 individuals in the four quadrats
Calculate the population density 

18. Quadrats
The calculated population density can be used to determine the estimated population size Estimated Population Size = DP x total study area What is the estimated population of trilliums?

19. Quadrats
What type of species do you think this method would be most useful for?
Useful for:
Sessile organisms or
Organisms with low motility

20. Mark-Recapture Population size (N) =
Animals are captured
Then, marked with a tag/collar/band
Released back into their habitat
Recaptured at later time (days/weeks)
 Watch this capture
Data is used to estimate the population size according to the following formula:
Population size (N) =
M (number originally marked) x n (total individuals in recapture)/
m (marked individuals in recapture)

21. Mark-Recapture Sample Problem 1
A group of researchers captured 20 warblers, which were marked with leg bands. They were released soon after. One week later, 50 warblers were captured. Of the 50 birds, 10 had bands on them. What would be their estimated population size?

22. Mark-Recapture
What type of species do you think this method would be most useful for? Useful for: Highly mobile populations

23. Population Dispersion
Dispersion:The population dispersion for a species is the pattern in which individuals in a population are distributed or spaced throughout an area.
Often related to density
Clumped Dispersion: occurs when individuals are concentrated in specific parts of the habitat
Often due to patchy resource distribution
May be social benefits ie. schooling fish

24. Population Dispersion
Uniform Dispersion: Individuals are spaced evenly throughout the habitat
Often due to intense competition. Eg. Nesting, feeding or mating territoriality, toxins released by plant roots

25. Population Dispersion
Random Dispersion: The population is spread out in an unpredictable manner that is unrelated to the presence of others
Least common and hardest to observe
Resources are not often distributed randomly

26. DONE!

27. Hold up! Dispersal patterns
Resource distribution is uniform
Resource distribution is clumped
Resource abundance varies
Resource abundance is scarce
Resource abundance is abundant
Interaction between members of a population is positive
Interaction between members of a population is negative
Interaction between members of a population is random.
Answers:
Random or uniform
Clumped
Uniform
Random
random