Teacher sheet · Ages 15–16 · about 45–50 minutes
Sampling a habitat
Lesson page: echoesof.science/school/habitats/ages-15-16/ · Pupil worksheet: echoesof.science/school/habitats/ages-15-16/print/
Learning aims
- Explain why ecologists sample and how random sampling avoids bias.
- Use frame quadrats and calculate percentage frequency; compare with percentage cover.
- Evaluate sample size, reliability and confounding variables in fieldwork.
- Link animal behaviour (woodlice kinesis) and habitat loss to survival.
Lesson plan
| Time | Activity |
|---|---|
| 5 min | Starter: how could you find out how many daisies are on the school field without counting them all? |
| 10 min | Read the text; practise frequency calculations. |
| 25 min | Quadrat survey outdoors. |
| 5 min | Calculate frequencies and compare areas. |
| 5 min | Quiz, or the Good sampling or bias? game as homework. |
Materials for the experiment
- Frame quadrats (0.5 m × 0.5 m, ideally divided into 100 squares with string)
- Two long tape measures
- Random number tables or a random-number app
- Simple plant identification key for playing fields
- Recording sheet and pencil
- Hand-washing facilities or sanitiser
Safety: Teacher checks the site for hazards (broken glass, holes, dog waste) and does a risk assessment. Cover cuts, do not eat outdoors, wash hands after handling plants and soil, use sun protection, and be aware of stings and allergies. Place quadrats; never throw them.
Common misconceptions
| Pupils may think… | Actually… |
|---|---|
| Throwing the quadrat gives a random sample. | Throwing is unsafe and not truly random; use random coordinates from two tapes, or drop it gently over your shoulder. |
| A bigger difference between areas proves trampling caused it. | Other variables such as light or soil moisture could differ; fieldwork shows correlation. |
| Percentage cover is the most accurate measure. | It is quick but subjective; frequency or presence/absence is more objective. |
Worksheet answers
- 6 ÷ 15 × 100 = 40%.
- A larger quadrat covers more ground, so it is more likely to contain a given species and gives a higher frequency; different sizes would not be comparable.
- Hypothesis, e.g. fewer species / lower frequency of tall plants where trampled. Random coordinates from two tapes in each area, at least 10 quadrats each, same quadrat size. Uncontrolled: light, soil moisture, soil compaction, mowing.
- Woodlice lose water quickly. They move more in dry places and slow down in damp ones, so they end up in damp places where they do not dry out and can keep breathing.
Quiz answers
- Why should quadrats be placed using random coordinates? To avoid bias, so the sample represents the whole area. Random sampling gives a fair estimate.[6]
- Daisies are found in 7 of 20 quadrats. What is their percentage frequency? 35%. 7 ÷ 20 × 100 = 35%.[7]
- What is the absolute minimum number of quadrats per sample area recommended by the Field Studies Council? 10. More quadrats reduce the effect of anomalies.[7]
- What is a weakness of estimating percentage cover? It is subjective and can overestimate flowering plants. It is faster but less objective.[7]
- Why do woodlice collect in damp areas? They move more in dry conditions and slow down in damp ones. This reflex response makes them gather where it is damp.[5]
- According to WWF, habitat loss is a main threat to about what share of threatened species on the IUCN Red List? 85%. It is probably the greatest threat to biodiversity today.[8]
Going further
Use a quadrat divided into 100 squares to estimate local frequency, or repeat the woodlice test to separate the effects of damp and dark. Discuss how you would sample a much larger habitat such as a woodland.
Sources used in this lesson
- [2] Habitat (National Geographic Education): reliability Medium-high
- [4] Polar Bear (San Diego Zoo Wildlife Alliance): reliability Medium-high
- [5] Woodlice habitats (Nuffield Foundation (Practical Biology)): reliability High
- [6] Biodiversity in your backyard (Practical Biology (Nuffield Foundation / Royal Society of Biology)): reliability High
- [7] Frame quadrats (Field Studies Council): reliability High
- [8] Habitat loss and degradation (WWF): reliability Medium-high
Full list with links and a note on each source's reliability: echoesof.science/school/habitats/sources/
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