POPULATION ECOLOGY Equation:
ECOLOGY - study of mutual interactions and environment P= estimated population
POPULATION ECOLOGY - focus on factors influencing M= total number of first sample
population size, growth rate, growth forms + distribution of S= total number of second sample
individuals T= number of marks in the second sample
- can be improved by repeating samples
DETERMINING POPULATION SIZE 𝑝=
𝑚×𝑠
𝑡
The choice of method will depend on: Methods of tagging:
→the accuracy required - paint non-toxic and waterproof (snails, tortoises)
→the type of organism - rubber rings on the legs of birds
→the specific habitat involved - plastic tags through the ears of buck
- shaving hair in a distinctive pattern
DIRECT METHOD Validity:
A total count of all individuals in a population “Don’t Venture Beyond Mixing Closed Populations”
Examples: 1. Don’t (Damage): Method should not damage or injure
1. . A census ( process of systematically collecting a the organism.
specific count of a particular population). 2. Venture (Visible): Marks should be clearly visible for the
⇒ In SA a census is taken every 5 years entire investigation.
2. Helicopters, used for large animals 3. Beyond (Behavior): Marking should not affect the
⇒ Elephants in a game farm organism’s movement or behavior.
3. Aerial photographs 4. Mixing (Mix): Marked organisms must mix well with the
⇒ seals in a colony or trees population before recapture.
5. Closed (Closed): The population must remain closed
Requirements: (no immigration or emigration).
● Sessile (fixed in one position) and Stationary 6. Populations (Period): Time between sampling should
● Slow moving be short to avoid births or deaths.
● Large animals
QUADRATS:
INDIRECT METHODS The quadrant method involves counting the individuals found in
involves sampling only part of a population a number of 1 m × 1 m squares that are randomly spaced over
> this tally/ count is used as a sample to estimate the total the total area.
population by means of calculation - Usually a square frame of known size
Two types: - The area where organisms must be counted is
A) mark-recapture method demarcated as TSA is determined
B) Quadrat technique - Quadrat is placed on the ground in the demarcated
area and the organisms concerned are counted inside
MARK RECAPTURE: the frame.
1. A specific area is demarcated 𝑛𝑢𝑚𝑏𝑒𝑟 𝑖𝑛 𝑠𝑎𝑚𝑝𝑙𝑒 𝑥 𝑠𝑖𝑧𝑒 𝑜𝑓 𝑤ℎ𝑜𝑙𝑒 ℎ𝑎𝑏𝑖𝑡𝑎𝑡
𝑛= 𝑡𝑜𝑡𝑎𝑙 𝑠𝑖𝑧𝑒 𝑜𝑓 𝑞𝑢𝑎𝑑𝑟𝑎𝑡/𝑠
2. A number of individuals are caught, counted and
marked- these are known as the first sample.
Precautions:
3. Release marked individuals (1st sample)
1. Exact number of organisms in each quadrat must be
4. Sufficient time must be allowed for marked individuals
known
to mix
2. The surface area of the quadrat mbk
5. Another group is captured (second sample)
3. Surface area of demarcated area mbk
6. The number of marked individuals in the second
4. Quadrat must be placed randomly.
sample is counted
, Importance of random sampling:
Every organism in a population must have an equal chance of
being selected.
Examples:
- Select each quadrant at random (turn your back on the
area and throw a stone over your shoulder – your
quadrant will be where the stone lands).
- Number in a hat etc.
IMPACT OF INTERACTIONS
PREDATOR-PREY
Feeding interaction where one organism, the predator hunts
SOCIAL ORGANIZATION:
and kills the other, prey.
- Improves reproduction and survival
To be socially organized, resources and activities must be
Predator prey graphs:
divided among groups.
Herding:
- Large group with collective behavior.
- Protection: Outside animals at risk, the center is safe.
- Matriarch: Oldest, most dominant female leads.
Packs:
- Strength in numbers for hunting and protection.
- Predators control prey numbers, but at the same time
- Smaller than herds.
available prey also control predator numbers.
- Alpha male leads with loyalty; rank order.
- Higher prey numbers = more predation
- less threat from competing predators, won't attack a pack
- Lower prey numbers= more death (shortage food)
Dominant breeding pair
⇒ predation is therefore a density dependent factor
- (alpha male & female) mate for life.
- non sexual members = care for pups
Large prey population→ carrying capacity is raised for the - Dominant female influences pack with pheromones.
predator → increase of the predator population. Now: prey - Disadvantage: Food sharing within the pack.
population decreases = predator population decreases→
because less food available→ carrying capacity of the
Eusocial Animals: Highest level of social organization
environment decreases. Predators either starve or emigrate.
- castes that perform different functions in colonies
- singular queen/ fertile female
South African examples: Termites:
Lion and zebra: - Live in large colonies, workers forage for food
Adaptations of lions: sharp teeth, power,agility - Soldier termite: protect colony
- Lions target old, injured,frail (survival of fittest)
→easier to catch & higher risk of dying to disease or starvation
FOOD WEBS:
Feeding relationships among organisms in an ecosystem
- Each step = trophic level
- Producers = 1st ; Consumers = rest
If one part of food web alters- the whole web will change
ECOLOGY - study of mutual interactions and environment P= estimated population
POPULATION ECOLOGY - focus on factors influencing M= total number of first sample
population size, growth rate, growth forms + distribution of S= total number of second sample
individuals T= number of marks in the second sample
- can be improved by repeating samples
DETERMINING POPULATION SIZE 𝑝=
𝑚×𝑠
𝑡
The choice of method will depend on: Methods of tagging:
→the accuracy required - paint non-toxic and waterproof (snails, tortoises)
→the type of organism - rubber rings on the legs of birds
→the specific habitat involved - plastic tags through the ears of buck
- shaving hair in a distinctive pattern
DIRECT METHOD Validity:
A total count of all individuals in a population “Don’t Venture Beyond Mixing Closed Populations”
Examples: 1. Don’t (Damage): Method should not damage or injure
1. . A census ( process of systematically collecting a the organism.
specific count of a particular population). 2. Venture (Visible): Marks should be clearly visible for the
⇒ In SA a census is taken every 5 years entire investigation.
2. Helicopters, used for large animals 3. Beyond (Behavior): Marking should not affect the
⇒ Elephants in a game farm organism’s movement or behavior.
3. Aerial photographs 4. Mixing (Mix): Marked organisms must mix well with the
⇒ seals in a colony or trees population before recapture.
5. Closed (Closed): The population must remain closed
Requirements: (no immigration or emigration).
● Sessile (fixed in one position) and Stationary 6. Populations (Period): Time between sampling should
● Slow moving be short to avoid births or deaths.
● Large animals
QUADRATS:
INDIRECT METHODS The quadrant method involves counting the individuals found in
involves sampling only part of a population a number of 1 m × 1 m squares that are randomly spaced over
> this tally/ count is used as a sample to estimate the total the total area.
population by means of calculation - Usually a square frame of known size
Two types: - The area where organisms must be counted is
A) mark-recapture method demarcated as TSA is determined
B) Quadrat technique - Quadrat is placed on the ground in the demarcated
area and the organisms concerned are counted inside
MARK RECAPTURE: the frame.
1. A specific area is demarcated 𝑛𝑢𝑚𝑏𝑒𝑟 𝑖𝑛 𝑠𝑎𝑚𝑝𝑙𝑒 𝑥 𝑠𝑖𝑧𝑒 𝑜𝑓 𝑤ℎ𝑜𝑙𝑒 ℎ𝑎𝑏𝑖𝑡𝑎𝑡
𝑛= 𝑡𝑜𝑡𝑎𝑙 𝑠𝑖𝑧𝑒 𝑜𝑓 𝑞𝑢𝑎𝑑𝑟𝑎𝑡/𝑠
2. A number of individuals are caught, counted and
marked- these are known as the first sample.
Precautions:
3. Release marked individuals (1st sample)
1. Exact number of organisms in each quadrat must be
4. Sufficient time must be allowed for marked individuals
known
to mix
2. The surface area of the quadrat mbk
5. Another group is captured (second sample)
3. Surface area of demarcated area mbk
6. The number of marked individuals in the second
4. Quadrat must be placed randomly.
sample is counted
, Importance of random sampling:
Every organism in a population must have an equal chance of
being selected.
Examples:
- Select each quadrant at random (turn your back on the
area and throw a stone over your shoulder – your
quadrant will be where the stone lands).
- Number in a hat etc.
IMPACT OF INTERACTIONS
PREDATOR-PREY
Feeding interaction where one organism, the predator hunts
SOCIAL ORGANIZATION:
and kills the other, prey.
- Improves reproduction and survival
To be socially organized, resources and activities must be
Predator prey graphs:
divided among groups.
Herding:
- Large group with collective behavior.
- Protection: Outside animals at risk, the center is safe.
- Matriarch: Oldest, most dominant female leads.
Packs:
- Strength in numbers for hunting and protection.
- Predators control prey numbers, but at the same time
- Smaller than herds.
available prey also control predator numbers.
- Alpha male leads with loyalty; rank order.
- Higher prey numbers = more predation
- less threat from competing predators, won't attack a pack
- Lower prey numbers= more death (shortage food)
Dominant breeding pair
⇒ predation is therefore a density dependent factor
- (alpha male & female) mate for life.
- non sexual members = care for pups
Large prey population→ carrying capacity is raised for the - Dominant female influences pack with pheromones.
predator → increase of the predator population. Now: prey - Disadvantage: Food sharing within the pack.
population decreases = predator population decreases→
because less food available→ carrying capacity of the
Eusocial Animals: Highest level of social organization
environment decreases. Predators either starve or emigrate.
- castes that perform different functions in colonies
- singular queen/ fertile female
South African examples: Termites:
Lion and zebra: - Live in large colonies, workers forage for food
Adaptations of lions: sharp teeth, power,agility - Soldier termite: protect colony
- Lions target old, injured,frail (survival of fittest)
→easier to catch & higher risk of dying to disease or starvation
FOOD WEBS:
Feeding relationships among organisms in an ecosystem
- Each step = trophic level
- Producers = 1st ; Consumers = rest
If one part of food web alters- the whole web will change
