1. Sampling Techniques and Measurements
National 5
Sampling Techniques and Measurements
Mr G Davidson

2. Sampling an Ecosystem We would sample an ecosystem to:
Find out which organisms live in it.
Find the abundance (how many) of these organisms.
Find out why these organisms live in this ecosystem.
Thursday, 15 November 2018
Mr G Davidson

3. Sampling an Ecosystem
When we are trying to find out the abundance of organisms, it is almost impossible to count every single individual, and so we take small samples.
In order to ensure this is valid, each sample area must be the same size.
We would take a number of samples to provide us with data to calculate the average.
Thursday, 15 November 2018
Mr G Davidson

4. Using a Quadrat
In order to sample plants (and slow moving animals) we can use a quadrat.
A quadrat marks off a small piece of ground of known area so that different plants present within this sample can be identified and counted or their area of cover estimated.
This sample gives us an idea of the number and kind of organism present in the whole area.
15 November 2018
G Davidson

5. Using a Quadrat
The quadrats we use are 0.25m2 and sub-divided into 25 smaller squares each 100cm2.
The quadrat is placed randomly on the ground.
The number of small squares containing the plant we are interested in are counted.
This is called the abundance estimate.
15 November 2018
G Davidson

6. Estimating Total Numbers
We can estimate the total numbers of organisms living in a certain area.
We need to calculate the area we are sampling.
15 November 2018
G Davidson

7. Estimating Total Numbers
We need to estimate numbers using the quadrat.
We then calculate an average number of organisms per quadrat.
We then work out how many quadrats fit into the specified area and multiply this number by the average number of organisms per quadrat.
15 November 2018
G Davidson

8. Estimating Total Numbers
Calculate the area of this field.
Length times breadth.
15m
40m
15 November 2018
G Davidson

9. Estimating Total Numbers
We now know the area of the field is: 15 x 40 = 600m2.
We now need to sample the field by using the quadrat , say 10 times.
The quadrat is then placed randomly in 10 different spots in the field, and the number of plants counted.
Suppose we are measuring daisies.
15 November 2018
G Davidson

10. Sampling Daisies
The quadrats are placed randomly and the number of daisies in each are counted.
15m
40m
15 November 2018
G Davidson

11. Sampling Daisies The results are collected and recorded.
We then calculate the average number of daisies per quadrat.
Add up the number of daisies column and divide by the number of sites.
Quadrat
Number of daisies 1 7 2 15 3 9 4 5 12 6 13 8 10 16
15 November 2018
G Davidson

12. Sampling Daisies
In this case the total number of daisies sampled was 90.
The number of sites was 10.
Therefore the average number of daisies per site is 90 ÷ 10 = 9 daisies
We now need to work out how many quadrats fit the field.
15 November 2018
G Davidson

13. Sampling Daisies
The field is 600m2 and there are 4 quadrats to each 1m2.
Therefore, the field is 600 x 4 = 2400 quadrats.
If there are, on average 9 daisies per quadrat, this means there are 9 x 2400 = daisies in the field.
A good estimate.
15 November 2018
G Davidson

14. Estimating Total Numbers
Here is one for you to try on your own.
This time we are estimating the number of worms in a field.
Here are the results.
Quadrat
No. of Worms 1 6 2 7 3 4 9 5 12 8 10
15 November 2018
G Davidson

15. Estimating Total Numbers
15 November 2018
G Davidson

16. How did you do? Average number of worms per quadrat?
Answer – 7 worms per quadrat.
Total area of field?
Answer – (50 x 40) – (25 x 15) = 1625m2
Total number of quadrats in field?
Answer x 4 = 6500 quadrats
Total number of worms?
Answer – 6500 x 7 = worms
15 November 2018
G Davidson

17. Sources of Error
When using quadrats, there are a number of mistakes which can be made.
Organisms wrongly counted.
Organisms wrongly identified.
Is it in the quadrat or not?
Number of samples too small.
Thursday, 15 November 2018
Mr G Davidson

18. Sources of Error We can minimise these errors in a number of ways.
Take a large number of samples and calculate averages.
This helps to make the results more reliable.
A key can be used to identify the correct organisms.
Have a rule to determine whether an organism is classed as in the quadrat or out, and stick to it for all quadrats.
Thursday, 15 November 2018
Mr G Davidson

19. Other sampling Techniques
Pitfall traps are used to trap small animals moving across the surface of the ground.
15 November 2018
G Davidson

20. Pitfall Trap
15 November 2018
G Davidson

21. Sources of Error Organisms in the trap may be eaten.
Cover the trap with a lid to try to keep predators from seeing them.
Some animals in the trap may eat others in the trap.
Either check the traps on a regular basis or put 50% ethanol in the trap to kill all animals and preserve them.
Thursday, 15 November 2018
Mr G Davidson

22. Other Sampling Techniques
Sweep netting is used to catch small animals living in vegetation.
Potato traps can be used to attract small animals, particularly snails and slugs.
Tree beating is used to remove organisms from branches.
Thursday, 15 November 2018
Mr G Davidson

23. Pond nets are used to catch animals living in ponds.
15 November 2018
G Davidson

24. Tullgren funnels are used to remove tiny organisms from soil samples.
15 November 2018
G Davidson

25. Pooter Pooters are used to capture small insects. 15 November 2018
G Davidson

26. Measurement of Abiotic Factors
Abiotic factors are non-living.
They tend to be climate related.
Light intensity can affect the distribution of organisms.
Some plants require very sunny conditions and others can survive in shady conditions.
Thursday, 15 November 2018
Mr G Davidson

27. Measuring Light Intensity
We can measure light using a Light meter.
Make sure you don’t cast a shadow on the meter or you will get a false reading.
Take a number of readings to calculate an average.
15 November 2018
G Davidson

28. Measuring Moisture We can measure moisture using a moisture meter.
Carefully push the probe vertically into the soil to a depth of approximately 4cm.
15 November 2018
G Davidson

29. Measuring pH We measure soil pH using a pH meter.
Carefully push the probe vertically into the soil to a depth of approximately 4cm.
Make sure the probe is cleaned between samples.
15 November 2018
G Davidson

30. Measuring Temperature
Soil temperature is measured using a soil thermometer.
The thermometer is pushed gently into the soil and left to settle, before a reading is taken.
Thursday, 15 November 2018
Mr G Davidson

31. Reducing Errors
It is important to try to reduce all possible sources of error, e.g.
Don’t hold the bulb of the thermometer.
Make sure the bulb is down into the soil.
Take a number of readings to get an average.
Thursday, 15 November 2018
Mr G Davidson

32. Identifying Organisms
It’s all very well counting organisms or collecting organisms.
Not all of them will be familiar to us.
In order to identify unfamiliar organisms, we would use a key.
There are different kinds of key.
We will use 2 kinds.
Branching Keys
Paired statement keys.
15 November 2018
G Davidson

33. Branching Keys These are pictorial.
At each stage you are given a choice of two things.
You pick the most appropriate and move to the next choice.
Eventually you should be left with the name of your organism.
Thursday, 15 November 2018
Mr G Davidson

34. Branching Keys Animals Legs No Legs More than 8 Legs 8 Legs Shell
No Shell
Spider
Centipede
Snail
Earthworm
Thursday, 15 November 2018
Mr G Davidson

35. Paired Statement Keys
Paired statement keys work in the same way as branching keys.
At each stage you are given a choice.
Make the appropriate choice and go to where you are asked to go.
Again, if the organism is present, you should end up with a name for it.
15 November 2018
G Davidson

36. Paired Statement Key Single leaf go to 2 Several leaflets go to 6
2. Leaf with prickles HOLLY
Leaf with no prickles go to 3
3. Leaf edge with lobes go to 4
Leaf edge with no lobes go to 5
4. Lobes sharp pointed SYCAMORE
Lobes rounded OAK
5. Leaf with smooth edge BEECH
Leaf with serrated edge ELM
6. Leaflets in fan shape HORSE CHESTNUT
Leaflets in pairs go to 7
7. Leaf edge serrated ROWAN
Leaf edge plain ASH
15 November 2018
G Davidson

37. Keys
The paired statement key is more manageable as it tends not to spread itself out as much.
The branching key is more pictorial and usually easier to use.
Try building your own keys for the following organisms. (Branching and Paired Statement!)
15 November 2018
G Davidson

38. Tulip Cockle Sycamore Dandelion Giraffe Gold finch Mackerel Seaweed
Spider
Sea Urchin
Venus Fly Trap
Cockatoo
15 November 2018
G Davidson