PAG03 = SAMPLING TECHNIQUES Flashcards
What is an explanation of random sampling?
This is where sample
sites are selected
randomly. using random numbers
as coordinates.
What are + and - of random sampling?
\+ prevents selective sampling + ensuring the data is not biased. - Not all areas/types of habitat may be sampled equally - Also, species with a small population may be missed, leading to an underestimate of biodiversity.
What are types of non - random sampling?
stratified, opportunistic, systematic
What is an explanation of stratified sampling?
In this method, the habitat is divided into groups that appear different. each area is sampled separately. mutually exclusive (each population can only be in one group) and collectively exhaustive (no population must be left out).
What is an example of stratified sampling?
if gorse patches are sampled separately from patches of bracken.
What are + of stratified sampling?
\+ all areas are sampled \+ prevents small populations from being missed out \+ It also allows areas of different population levels in the same habitat to be sampled equally
What are - of stratified sampling?
-This may lead to some over-representation of some areas in the study, for example small areas may be sampled more than necessary because they look different from other areas.
What is an explanation of opportunistic sampling?
areas are chosen to sample by either using their prior knowledge, or choosing areas that interest them as they are collecting data.
What are + of opportunistic sampling?
+This is easier and
quicker than random
sampling +produces
more data.
What are - of opportunistic sampling?
-potential for bias.
- Species which are more
noticeable (e.g. due to
size or being colourful)
may be included more leading to an
overestimation of their
importance
What is an explanation of systematic sampling?
samples are taken at set distances (e.g. every 5 metres). An example of this is using a transect.
What are + of systematic sampling?
This is good to view a
change in biodiversity
or populations along a
line
What are - of systematic sampling?
risk of missing species as only a small area is sampled. This could cause biodiversity to be underestimated
How do you collect data for species diversity?
- Select area for sampling.
- Place two long tape-measures at right angles to each other along the border
- Randomly generate numbers to decide where to sample.
- To sample at each random location, place the left-hand corner of the quadrat at the
position where the two coordinates meet/intersect. - Identify the different species in the quadrat using a key
- Generate new coordinates and repeat the sampling process at least 9 times more.
- Use Simpsons index of diversity to calculate the species diversity (
What is species diversity?
measure of the number of different
species in a given community
What is species abundance?
amount of a certain species in a specific habitat.
How do you collect data for species abundance?
Perform steps 2-6 of the above species diversity method
The population size of each species can be estimated by multiplying up the sample
size.
3. Produce a graph of species abundance in different areas.
What is species abundance and distribution?
Species distribution is a measure of where species are located / how species are distributed.
How do you collect data for species abundance and distribution?
. Use a measuring tape to make a transect over the area
2. Place quadrats at given intervals along the tape measure. The
bottom left-hand corner of each quadrat should be touching the relevant metre
mark, and the left-hand edge runs along the tape measure (so the quadrats should
be to the right of the tape measure).
3. Identify the different species in each quadrat using a key and count the number of
each present. Calculate the percentage cover. Record in a table.
4. Produce a graph of species distribution against distance along transect (e.g. a kite
diagram).
