1. 12.1 Population Characteristics
SBI 4U1 – Population Dynamics

2. Learning Goals
To learn the factors that affect population distribution
To be able to calculate population density and population size
To learn about quadrat and mark-recapture sampling methods
To understand the potential ethical concerns that arise from studying wildlife populations

3. Population Ecology
Pop’n of white-tailed deer is increasing in urban areas
Problematic for both deer and humans
Population ecology studies population size, density, distribution, and changes over time
Analyze real life situations; also construct models
Links to many other fields in biology

4. Population Distribution
Described by 3 factors:
Geographic range
Population size & density
Distribution of individuals

5. Geographic Range Total area occupied by a pop’n
Eg. Rat-eating pitcher plant (Nepenthes attenboroughii) found on Mount Victoria in the Philippines
Includes habitat

6. Population Size and Density
Nt (population size): number of individuals of a species at a given time
D (population density): number of individuals per unit area/volume
Species with a large body size tend to have a lower pop’n density (elephants vs. E. coli)
Also must consider usable/used space within a habitat: crude density vs. ecological density

7. 2.18 𝑥 108 𝑏𝑙𝑎𝑑𝑒𝑠 𝑜𝑓 𝑔𝑟𝑎𝑠𝑠 4 ℎ𝑎 = 5.45 x 107 blades of grass/ha
Calculating Density
𝑫= 𝑵 𝑺
Where N = # of individuals and S = space occupied
For example:
8 ℎ𝑜𝑟𝑠𝑒𝑠 4 ℎ𝑎 = 2 horses/ha
2.18 𝑥 108 𝑏𝑙𝑎𝑑𝑒𝑠 𝑜𝑓 𝑔𝑟𝑎𝑠𝑠 4 ℎ𝑎 = 5.45 x 107 blades of grass/ha

8. Population Dispersion
Spatial distribution of individuals within a geographic range
3 theoretical patterns:
Clumped: individuals in small groupings
Random: organisms distributed independently
Uniform: regular distribution of individuals

9. Studying Populations
Scientists need to manage populations for many reasons:
Endangered species
Economically important species
Agricultural pests
Counting techniques vary depending on species size, location, movement of individuals, etc.
Direct counting, aerial counting, extrapolation, tracking, nests, fecal droppings

10. Sampling Populations
More accurate sampling techniques have been developed in cases where an accurate estimation is required, or in the case of highly mobile pop’ns
Quadrat sampling
Mark-recapture method

11. estimated pop’n density = 𝑡𝑜𝑡𝑎𝑙 # 𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙𝑠 𝑠𝑎𝑚𝑝𝑙𝑖𝑛𝑔 𝑎𝑟𝑒𝑎
Quadrat Sampling
Effective for small/immobile pop’ns
A quadrat is a square placed randomly in the area (avoids bias – multiple quadrats used)
Size depends on size of pop’n being sampled
estimated pop’n density = 𝑡𝑜𝑡𝑎𝑙 # 𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙𝑠 𝑠𝑎𝑚𝑝𝑙𝑖𝑛𝑔 𝑎𝑟𝑒𝑎
estimated pop’n size = (est. pop’n density)(total size of sampling area)

12. Example
You want to estimate the pop’n size and density of maple trees in a forest measuring 400m by 250m. 6 quadrats (5m by 5m) are placed randomly, and you count 1, 3, 0, 2, 2, and 4 trees in the quadrats.

13. estimated pop’n size = (0.08 trees/m2)(100, 000 m2)
estimated pop’n density = 𝑡𝑜𝑡𝑎𝑙 # 𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙𝑠 𝑠𝑎𝑚𝑝𝑙𝑖𝑛𝑔 𝑎𝑟𝑒𝑎 estimated pop’n density = (25𝑚2) estimated pop’n density = 0.08 trees/m2
estimated pop’n size = (est. pop’n density)(total size of sampling area)
estimated pop’n size = (0.08 trees/m2)(100, 000 m2)
estimated pop’n size = 8000 trees

14. Mark-Recapture Sampling
Effective for highly mobile species
A specific number of individuals are captured, marked/tagged in some way, and released back into the pop’n
After a given period of time (allowing for marked animals to mix with unmarked), another random sample is captured
Proportion of marked:unmarked can be used to estimate size of entire pop’n

15. Accuracy depends on 5 assumptions:
Chances for individuals to be caught must be equal (initial and recapture)
Proportion of marked:unmarked must remain the same (no birth/death or migration)
Sufficient time for dispersal before recapture (balance between #1 and #2)
Marks/tags do not adversely affect animals
Marked animals do not lose their marks

16. M = total # animals marked in first sample
N = total pop’n size
M = total # animals marked in first sample
n = total # animals captured in second sample
m = # marked animals in second sample
Biologists wanted to quantify the number of Chinook salmon in Lake Ontario. They captured, marked, and released 50 fish, then waited for them to redistribute in the population. 150 fish were captured in the second sample, of which 17 were marked.
N = 50(150) 17
N = approx. 441 salmon

17. Tracking Methods
Tracking allows scientists to discover other valuable information about animal behaviour
Can be accomplished using:
GPS (collars, leg bands, harnesses, glue/tape)
DNA sampling
Droppings/other biological materials

18. Ethical Concerns
There is some debate as to whether capturing, handling, and/or tagging animals will alter their behaviour or affect reproductive ability (recall sexual selection: different scent, odd-looking tags, etc. may impact mate selection)
A study has shown flipper bands on King penguins reduced their lifespan and reproductive fitness
Trapping methods may be harmful, esp. if tranquilizers are needed
Canadian Council on Animal Care (CCAC) sets ethical guidelines; encourages minimally invasive techniques and computer simulations whenever possible