Part 1 of 2Sampling techniques and minimizing error
| Sampling Technique | Target Organisms | Sources of Error | How to Minimise Error / Ensure Reliability |
|---|---|---|---|
| Quadrats | Stationary or slow-moving organisms (plants, ground cover) | Non-random placement (biased results); miscounting overlapping plants | Throw/place quadrats randomly (using coordinates or random number generators); establish a consistent rule for plants crossing borders; repeat multiple times to calculate a reliable average. |
| Pitfall Traps | Small ground-dwelling invertebrates (beetles, spiders, woodlice) | Trap opening not level with soil; organisms drown in rain; predators eat trapped prey; organisms escape | Set trap opening flush with ground surface; camouflage with a raised lid/stones (keeps rain and birds out); punch drainage holes in bottom; check and empty trap frequently. |
Part 2 of 2Paired-statement keys and indicator species
Paired-statement keys
- Identification guides consisting of numbered pairs of alternative contrasting statements based on observable physical characteristics.
- Following the instructions at the end of each chosen statement leads sequentially to the correct identification of the organism.
Indicator species
- Species whose presence, abundance, or absence provides measurable information about environmental quality and pollution levels in an area.
- Air pollution indicators (Sulfur dioxide, SO2):
- Crustose lichenstolerant of high pollution (found in urban/industrial zones).
- Foliose / Fruticose (shrubby) lichens
- highly sensitive to SO2;
- only survive in exceptionally clean air.
- highly sensitive to SO2;
- Freshwater pollution indicators (Dissolved oxygen / organic waste):
- Stonefly nymphs and Mayfly larvaerequire high dissolved oxygen levels (clean, unpolluted water).
- Freshwater shrimpmoderately clean water.
- Bloodworms and Sludgewormssurvive in severely polluted, low-oxygen waters.
Key terms
| Term | Meaning |
|---|---|
| Quadrat | A square frame of known area used to sample plant and sessile organism populations. |
| Pitfall trap | A container sunk into the ground to trap small crawling surface invertebrates. |
| Indicator species | Organisms whose presence or absence reveals environmental quality and pollution levels. |
| Reliability | The extent to which repeated experimental measurements under identical conditions yield consistent results. |
Avoid these mistakes
Avoid these mistakes
Placing quadrats deliberately rather than randomly — samples must be chosen randomly to represent the entire habitat without bias.
Leaving pitfall traps uncovered — traps must have a raised stone lid to prevent birds eating trapped animals and avoid rain drowning them.