1. Characteristics of Populations
SBI4U
Miss Richardson

2. Population Size and Density
Populations are constantly in flux. They move, change and are influenced by their environment
Various ecosystems and their abiotic components make up a biome
Together, biomes make up the biosphere

3. Ecology Terminology

4. Biomes of the World

5. Population Size & Density
World Population Density Map

6. Population Size, N
Population size is the total number of organisms of the same species
It is determined by actual counting (census) or by estimation

7. Population Density, Dp
Is the number of individuals per unit of volume or area
It can be calculated by:
Dp = N/A

8. Crude vs. Ecological Density
Crude density refers to the total number of organisms per total area
Ecological density refers to the number of organisms in the actual space used by the population

9. Example
If 22 fox live in a small national park which is 300 hectares and 250 hectares without the lake, calculate the crude and ecological density.

10. Example Crude Density D = N S D = 22 foxes 300 ha = 0.07 foxes /ha
Ecological Density D =  N         S
D =  22 foxes          250 ha     = 0.08 foxes /ha

11. Determining Population Size
There are three main techniques for determining population size:
Transects
Quadrats
Mark-Recapture

12. Transects
Samples populations along a long rectangular area/line of specific length
The species being monitored are counted and recorded
Useful when density of a species is low or when individual organisms are very large (ie: trees)

13. Quadrats
A small square area is measured in which individuals are counted and extrapolated for the whole area
Most effective for stationary populations

14. Mark-Recapture
A number of organisms are caught and marked (or tagged with technological devices) and returned to the environment
They are later recaptured and the numbers are compared to the original capture:
Total #marked = #marked recaptured
total population size of recapture

15. Example
You are part of a summer research team and in trying to count the number of catfish in a lake you capture 29 fish and tag them.  Then a week later you catch 35 fish and of those only 10 are tagged.  Estimate the population size.

16. Example
Total # of Marked (M) =   #marked recaptured (m) Total population (N)             size of recapture (n)
M = 29 m = 10 n = 35
29  =  10 N        35
N = is approximately 102 fish.

17. Population Distribution
There are 3 recognized distribution patterns
Uniform
Random
Clumped

18. Clumped Distribution
Occurs due to uneven distribution of resources – populations gather around them
Common among species that travel in groups

19. Uniform Distribution
Occurs when resources are scarce, but evenly distributed
Usually a result of negative interactions among population members

20. Random Distribution
Occurs when resources are plentiful and uniformly distributed
Results from neutral interactions amongst individuals

21. Life Histories and Populations
Ecologists rely on survivorship and reproductive patterns to help them understand populations – these patterns are referred to as life histories
Life histories vary between species
They are described based on:
Fecundity – average number of offspring produced by a female over her lifetime
Survivorship - #/% of organisms that typically live to a given age