4️⃣PAG 3: Sampling techniques

Question 1

Safety (3)

Answer 1

Follow local rules on working in an outside environment and wash hands after lesson.
When any fieldwork is undertaken, work in groups and be aware of hazards in the specific environment.
Sensible footwear and clothing should be worn. If the weather is hot and sunny, sunscreen and hats are required.

Wash hands thoroughly after the experiment.
Be aware of any allergies to plants that students may have.
Be careful when handling plants and insects as they may have sharp edges/sting.

Question 2

Equipment

Answer 2

• two 20 m measuring tapes
• table of random numbers or other generator of random numbers
• 50  50 cm gridded quadrat frame
• notebook and pencil
• identification sheet
• optional equipment to measure abiotic factors, such as light meter, pH meter/ universal indicator paper, anemometer.

Question 3

What to do when

• studying area of school field
• see how distribution of organisms is affected by abiotic factors

Answer 3

In this practical you will use random sampling to study an area of the school field. This will allow you to estimate the population of your species over the whole area.
You will then need to carry out sampling along a transect to see how the distribution of your organisms is affected by abiotic factors.

Question 4

What sampling means

Answer 4

It is very difficult to count all the living organisms present in a particular environment, especially if the organisms are moving and/or the area is large. To overcome this difficulty, we use samples.
Sampling means taking observations or measurements from a small area, which is representative of the larger area. These can then be used to estimate the abundance (number) or distribution of selected organisms.

Question 5

Method 1

Answer 5

Method 1
1. Use a random number generator to obtain 2 numbers, which are to be used as coordinates to find a location on the 2 tape measures set up.
2. Set down the quadrat at the coordinates.
3. Count and record the number of the required plant species in the quadrat.
4. Repeat steps 1-3 to take 9 more samples.
5. Estimate the population size using this formula:
total area / area of quadrat x mean number of individuals in a quadrat
6. Repeat steps 1-5 at another site with different abiotic factors eg. mown vs unmown.

Question 6

Method 2

Answer 6

Method 2

1. Write down a hypothesis of the effect of a change in an abiotic factor (eg. light intensity) on the distribution of the plant species.
2. Lay down a tape measure from the base of a tree to an open area of ground/ along a location with an ecological gradient.
3. Place the quadrat along the ‘0’ end of the tape measure, with one corner touching the ‘0’ mark.
4. Count the number of each species of plant using a key and record it in a table as seen below.
5. Test the abiotic factor that changes along the transect. For example:
   - Light intensity
   - Compacting (how far a nail can be pushed into the soil)
   - Temperature
   - Moisture content
   - Soil pH
6. Place the quadrat 5 m up the tape measure and repeat steps 4-5.
7. Repeat step 4 at 5 m intervals until you reach the end of the transect line.
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   8. Gather data from your class to find the mean number of plants at each point along the transect.
8. Plot a graph of ‘number of plants’ against the ecological gradient that is observed as the distance along the transect line increases. Compare your results to your hypothesis.

Question 7

Sources of error

Answer 7

Without repetitions, the results from only one belt transect may be anomalous and not reliable. Some organisms may be too small or difficult to identify.