Chapter 9
p. 292-309
Population and Communities
Studying Populations
- Definition: ________________________________________________________________________________
______________________________________________________________________________________________
They have a lot of interactions and share the same resources:
- Water, food, sunlight…
To describe a population the area that is occupied needs to be specified.
- Three main characteristics used to describe populations:
A) ___________________________
B) ___________________________
C) ___________________________
A) Population Size
- Definition: _____________________________________________________________________________________.
Population size is affected by births, deaths, immigration and emigration.
- Birth: _________________________________________
- Death: ________________________________________
- Immigration: _____________________________________________________________________________
______________________________________________________________________________________________
- Emigration: _______________________________________________________________________________
______________________________________________________________________________________________
The population size will remain the same if:
__________________ + ______________________ = ______________________ + __________________________
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Chapter 9
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Measuring Population Size
A number of methods exist to measure the size of populations. The most common
methods are counting individuals, counting by sample area and mark-recapture.
1. Counting Individuals
- If possible, count all the individuals within the area occupied by the
population.

______________________________________________________________________

______________________________________________________________________
OR
2. Counting by Sample Area
- ___________________________________________________________________________________________
A) Section off sample area into quadrats (rectangular areas marked off with
rope or ribbon).
B) The number of individuals are counted in that area and used in the
equation below:
Population size =
Example: quadrat is a rectangle (3 m x 4 m = 12 m2), total study area (100 m x
72 m = 7200 m2), average number of individuals (40)
Population size = ________________________________________________________________________________
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3. Mark and Recapture
Method used when population moves a lot (sharks, fish etc…)
1. Catch individuals (nets or cages).
2. ___________________________________________________________________________
3. ___________________________________________________________________________
4. Recapture individuals (nets or cages).
5. Count the individuals with separate count for marked individuals.
6. ___________________________________________________________________________
Population size =
Example: 30 ducks are captured, marked and released. If on the second capture,
10 of 40 captured ducks are tagged (marked), then the population of ducks is
estimated to be:
B) Population Density
Definition: ________________________________________________________________________________________
______________________________________________________________________________________________________
- Example: there are 21 white-tailed deer per square kilometer on the island
of Anticosti.
Population Density Example
a) Area: A population of 10 000 maple trees is contained within a 300 km2
forest. The density of the maple tree population is 33.3 maple trees per km2 .
b) Volume: A pond contains 2500 L of water and 17 lily pads. The density of lily
pads is 0.0068 lily pads per liter of water.
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Chapter 9
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The density of a population can vary depending on the habitat.
a) The presence of predators, parasites or disease can affect the density.
- Increased presence of predators, parasites or disease = ___________________________
- Decreased presence of predators, parasites or disease = __________________________
b) Natural or “man-made” disasters can affect the density.
- Deforestation = ______________________________
c) The climate and resources within the habitat can affect the density.
- More resources = ___________________________________
- Fewer resources = __________________________________
C) Population Distribution
Definition: ________________________________________________________________________________________
______________________________________________
Three types of population distribution
- ________________________________________
- ________________________________________
- ________________________________________
Population Distribution
A) clumped: most common, occurs when certain areas of the habitat offer
better living conditions (shelter, food, water …)
Example: fish moving in schools.
B) uniform: ______________________________________________________________________________.
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Example: certain birds are uniformly distributed to allow each bird a
certain minimal territory.
C) random: ____________________________________________
Example: bushes and trees are randomly dispersed because they
cannot clump together or spread out uniformly.
Ecological Factors
Definition: ________________________________________________________________________________________
______________________________________________________________________________________________________
Different factors of a habitat can affect the individuals of a population 
population density affected.
2 types of ecological factors:
A) abiotic (non-living): _________________________________________________________________________
B) biotic (living): _________________________________________________________________________________
______________________________________________________________________________________________________
Abiotic factors: soil or water pH, amount of light, depth of snow, temperature, air
humidity, terrain (land topography).
Biotic factors: predation, birth rate, disease, amount of food, competition, human
activity.
Limiting Factor: If the effect of the factor is dramatic
(reduces the population density or prevents its growth),
the ecological factor is called the limiting factor.
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Chapter 9
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Definition: ________________________________________________________________________________________
______________________________________________________________________________________________________
An ecological factor becomes limiting if:
1. ________________________________________________ (no sunlight)
2. ________________________________________________ (too cold – not enough heat)
3. ____________________________________________ (too much water causes cactus root to rot)
Biological Cycles in Populations
•
Definition: ________________________________________________________________________
______________________________________________________________________________________
Example: The population of the hare and the lynx rise and fall together.
The hare population rises  the lynx have more food  reproduce a lot 
lynx population increases  more hares are hunted  hare population
decreases  less food for the lynx  lynx population decreases  hare
population increases etc….
Studying Communities
•
Definition: ___________________________________________________
______________________________________________________________________________________
Biodiversity
Definition: ________________________________________________________________________________________
______________________________________________________________________________________________________
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Chapter 9
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We must consider the following to measure biodiversity:
1) The number of species in the community (species richness).
2) Relative abundance of each species,
meaning the number of individuals of
a particular species in relation to the
total number of individuals in the
community.
Factors affecting Biodiversity
- The biodiversity of a community is high when:
o
_____________________________________________ (NOT the number of individuals)
o
The relative abundance of different species is similar (percentage of
each species is similar across species)
Four main types of interaction between individuals in a community are:
- __________________________________
- __________________________________
- __________________________________
- __________________________________
Competition
Definition: ________________________________________________________________________________________
______________________________________________________________________________________________________
Example of resources: limited precipitation in a desert allows for competition
between plant species.
Competition cannot exist without _______________________________________ (resource).
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2 Types of Competition
- Intraspecific competition occurs between individuals of the ____________ species.
- Interspecific competition occurs between individuals of _________________ species.
Predation
•
Definition: ________________________________________________________________________
______________________________________________________________________________________

Predator (the one eating) versus prey (the one being eaten)
Mutualism
•
Definition: ________________________________________________________________________
______________________________________________________________________________________
Commensalism
Definition: commensalism is the interaction between two living organisms in which
one organism benefits from the relationship, while the other remains unaffected.
Type of Interaction
Competition
Predation and Parasitism
Mutualism
Commensalism
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Effect on Population A
Effect on Population B