11.2 Flashcards
1
Q
What is sampling?
A
- Means taking measurements of a limited number of individual organisms present in a particular area
- Sampling can be used to estimate the number of organisms in an area without having to count them all as that would be too time consuming
2
Q
What is random sampling?
A
- means selecting individuals by chance
- In a random sampling, each individual in the population has an equal likelihood of selection
3
Q
How can random sampling?
A
- Mark out a grid with two tape measures laid at right angles
- Use random numbers to determine the x coordinate and the y coordinate on your grid
- Take a sample at each of the coordinate pairs generated
4
Q
What is non random sampling?
A
alternative sampling method where the sample is not chosen at random
5
Q
What is opportunistic sampling?
A
Weakest form of sampling as it may not be representative of the population- uses organisms that are conveniently available
6
Q
What is stratified sampling?
A
- Some populations can be divided into a number of strata (sub groups) based on a particular characteristic.
- A random sample is then taken from each of these strata proportional to its size
- we can use a belt transect with quadrats at regular intervals across the different areas
7
Q
What is systematic sampling?
A
- different areas within the overall habitat are identified, which are then sampled separately
- overall habitat are identified, which are sampled separately
- Taken along a belt transect
- measures how species change along the transect
8
Q
Why aren’t samples always reliable?
A
- sampling bias- the selection process may be biased, this can be removed by reducing human intervention
- Chance- the organisms selected may not be representative of the whole population- this can be minimised by having a larger sample size therefore making results more reliable
9
Q
What are the ways we can count what’s inside a quadrat?
A
- subjective rating
- percentage cover
- percentage frequency
- species density
