Sampling techniques Flashcards
When is representative sampling used?
Used when you want a representative sample of the whole area under study.
How is random sampling carried out?
1) Measuring tapes are placed along 2 sides of the area, (like the axes of a graph)
2) Random numbers from a computer are used as coordinates to choose sampling points in the area.
3) Alternatively, random numbers can be used as polar coordinates (angle and distance) starting from a central point.
Why should there always be a large sample?
At least 10, preferably 100. To minimise the chance of picking a skewed sample and to allow for bad measurements or anomalies.
How much should you aim to sample?
One should aim to sample at least 2% of the total area, so if the field area was 500 m2, you would need to sample 10% of the area altogether.
When is systematic sampling used?
Used when you choose where to take your samples because you are investigating a specific pattern in the ecosystem, such as zonation in a rocky shore.
What is the most common type of systematic sampling?
Transect sampling
What is transect sampling?
Where samples are taken along a straight line to see what changes there are along the line.
What does a transect follow?
A transect normally follows an environmental gradient, e.g. down a rocky shore, into a forest or down a mountain slide.
What is a line transect?
In a line transect the organisms touching a piece of string stretched along the transect are recorded.
What is a belt transect?
Quadrats are placed at intervals along the transect and organisms in each quadrat are counted.
What happens in an interrupted transect?
In an interrupted transect, the sampling is not continuous but there are gaps between the sample.
Advantage and disadvantage of line transect.
Quick
Can be unrepresentative
Advantage and disadvantage of belt transect
Can generate more complete data
But involves more work
How can data from a transect be represented?
Data from a transect can be represented as a kite graph which shows biotic data as kites adn abiotic data as lines.
Regardless of the sampling sites are chosen what should be measured?
However the sampling sites are chosen, both biotic and abiotic factors should be measured at each sampling site. The combination of the 2 measurements gives a more detailed understanding of the ecosystem.
