Density independent:
● Greater effect (crowded)
- Resource competition
- Found by predators = environmental resistance
- Disease/ parasite spread
Stable/ unstable populations:
● Stable population → fluctuates around carrying capacity
● Unstable population → exceeds carrying capacity
- Habitat deterioration
- Extinction
Estimating population size
Direct methods:
● Counting each individual → census
● Used for:
- Large organisms
- Area not too large
- Slow moving, stationary or fixed position
● Too large:
, - Aerial photograph
- Helicopters
Indirect methods:
1. Quadrat method
● N = number in sample x habitat size
quadrat size
● Method:
- Measure total area
- Use wooden frame as quadrat
- Distribute quadrats randomly
- Count individuals in each quadrat
- Calculate population size
2. Mark-recapture method
● P=MxC
R
● Method:
- Mark out area
- Capture individuals and mark them
- Release them back into environment
- Wait for them to mix
- Recapture individuals
- Count total and marked total
- Calculate population size
● Precautions:
- Short time between sampling → no births/ deaths
- Repeat several times → average
- Marking must not damage individual
- No immigration/ emigration
Predator-prey relationships
● Predator:
- Regulates abundance & distribution of prey
- Increases biodiversity
- Keeps prey genetically fit
- Provides food for scavengers
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