Sampling techniques for populations Cambridge IGCSE Environmental Management revision
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In plain words
You cannot count beetles with a ruler or trees with a jam jar. Each technique here suits a particular kind of organism, and half the marks in a fieldwork question come from picking the right one and knowing what could go wrong with it.
9 things to know
- A quadrat is a square frame placed on the ground. The plants or slow-moving animals inside it are counted, or the percentage of the frame that each species covers is estimated.
- A transect is a line, such as a tape, laid across a habitat. Samples are taken along it, to show how species change from one end to the other.
- A pitfall trap is a container sunk into the ground with its rim level with the surface. Small animals that walk on the ground fall in. A cover keeps out rain and predators.
- A pooter is a small jar with two tubes. The user sucks on one tube and a small insect is drawn up the other into the jar. A mesh stops the insect being swallowed.
- A sweep net is swept through long grass or leaves to catch insects.
- Aerial photography and drones photograph large areas from above. They are used to count large animals and to map vegetation, in places that are hard to reach.
- Automated sampling uses equipment that records by itself, such as cameras triggered by movement. It works day and night without disturbing the animals.
- Limitations. Quadrats are no use for animals that move fast. Pitfall traps catch only animals on the ground, and trapped animals may eat each other. Sweep nets miss insects that fly away, and results depend on the person sweeping.
- Drones and automated equipment are expensive, the images take time to analyse, and small or hidden animals are missed.
Worked example
Suggest a technique for each: daisies on a lawn, beetles on a woodland floor, elephants in a large reserve.
- Daisies do not move, so use quadrats, placed at random, and count the daisies in each.
- Beetles walk on the ground, so use pitfall traps, checked each morning.
- Elephants are large and spread over a huge area, so count them from aerial photographs or with a drone.
Tips and tricks
- A quadrat samples an area. A transect is a line. They are often used together: quadrats placed at intervals along a transect.
- When asked for a limitation, make it fit the technique. "It takes a long time" is weak. "Flying insects escape from a sweep net" earns the mark.
It lands in your notebook with its questions as flashcards.
Sampling techniques for populations: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
What is a quadrat?
Organisms inside the frame are counted.
Which technique catches beetles walking on the ground?
They fall into the sunken container.
What is a pooter used for?
The insect is sucked gently into a jar.
What does a transect show?
It is used where conditions change gradually.
Which technique suits counting large animals in a remote area?
Photographs from above cover a large area.
Ten quadrats of 1 m² hold a mean of 6 daisies each. Estimate the number of daisies in a 200 m² lawn.Stretch
6 per m² × 200 m² = 1200.
Quiz
6 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 7 marks. Write your answers on paper, then check them.
Sampling techniques for populations
Cambridge IGCSE Environmental Management 0680 · 7 marks · papermunch.org
Name ______________________________ Date ______________
Describe how a pitfall trap is set up and used.[3]
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A container is sunk into the ground with its rim level with the soil surface. A cover is placed over it, raised a little, to keep out rain. It is left, and the animals that have fallen in are identified and counted.
Explain how a quadrat is used to estimate the number of plants in a field.[2]
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Quadrats are placed at random and the plants in each are counted. The mean per quadrat is scaled up to the area of the whole field.
Give one benefit and one limitation of using a drone to survey animals.[2]
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Benefit: it covers a large or hard-to-reach area quickly, with little disturbance. Limitation: it is expensive (or: small animals and those under trees are missed).
Answers: Sampling techniques for populations
- 1. A container is sunk into the ground with its rim level with the soil surface. A cover is placed over it, raised a little, to keep out rain. It is left, and the animals that have fallen in are identified and counted.
- 2. Quadrats are placed at random and the plants in each are counted. The mean per quadrat is scaled up to the area of the whole field.
- 3. Benefit: it covers a large or hard-to-reach area quickly, with little disturbance. Limitation: it is expensive (or: small animals and those under trees are missed).