11.2 - Types of Sampling

Question 1

What is sampling?

Answer 1

• Taking measurements of a limited number of individual organisms present in an area
• Used to estimate number of organisms of area (without counting)
• Measures specific characteristics of an organism, e.g. height of a wheat plant, not reliable to measure one > sample n amount and take an average.
• Sampling results - used to make estimates about organism number, species distribution or measured characteristics throughout a habitat.

Question 2

Define organism abundance

Answer 2

Abundance of an Organism: Number of individuals of a species present in an area

Question 3

Define and give an example of a random sampling practical procedure.

Answer 3

Definition: Sampling where each item has an equal chance of likelihood

• To decide which organisms to study, use a random number table or a computer can generate it for you

1. Mark out grid on grass using tape measures
2. Use random numbers to allocate which coordinate reference to use
3. Take a sample at each coordinate reference generated

Question 4

Define non-random sampling

Answer 4

Alternative sampling method (not random), either opportunistic, stratified or systematic.

Question 5

Give features/characteristics of opportunistic sampling.

Answer 5

• Weakest sampling form – may not be representative of the whole population
• Uses organisms that are conveniently available at that specific time and location

Question 6

What is stratified sampling?

Answer 6

• Population is divided into strata (sub-groups), based on e.g. characteristics such as male/female. Random sample of each strata is taken proportional to population size.

Question 7

How is systematic sampling performed?

(Line transect, belt transect)

Answer 7

• Samples different areas in a systematic method (e.g. areas within a habitat a sampled)
• E.g. Studying how plant species change as you go inland from sea – sample every 100 metres.
• Often carried out across a line transect (line is marked along a ground, samples taken every metres) or a belt transect (two parallel lines drawn, samples taken at every metres, but the area at each point is sampled). Reliability

Question 8

Give 2 reasons why samples are not representative of the whole population and how these issues can be mitigated

Answer 8

Bias - selection process could be bias.

• To remove sampling bias, use random sampling and remove human choice of the areas samples

Chance - organism that is selected by chance, may not represent the population.

E.g. 5 worms selected in a trap, may be by chance the 5 longest.

Greater sample size = more reliable results