Apparatus & Techniques: Random Sampling Flashcards
Sampling is a method of investigating the
abundance and distribution of species and populations
There are two different types of sampling
Random
Systematic
In random sampling the positions of the sampling points are
and what are the benefits
sampling points are completely random or due to chance
This method is beneficial because it means there will be no bias by the person that is carrying out the sampling that may affect the results
In systematic sampling the positions of the sampling points are chosen
what are the disadvantage of this
by the person carrying out the sampling
There is a possibility that the person choosing could show bias towards or against certain areas
Individuals may deliberately place the quadrats in areas with the least species as these will be easier and quicker to count
This is unrepresentative of the whole area
When a sampling area is reasonably uniform or has no clear pattern to the way the species are distributed then
random sampling is the best choice
Some ecosystems are very complex with large numbers of different species of different sizes
For the sake of logistics, sampling is often used to estimate the
distribution and abundance of species
The distribution of a species describes
how it is spread throughout the ecosystem
The abundance of a species is the number
of individuals of that species
When carrying out sampling, square frames called quadrats can be used to mark off the area being sampled
Quadrats of different sizes can be used depending on what is being measured and what is most suitable in the space the samples are being made in
Quadrats must be laid
randomly in the area to avoid sampling bias
This random sampling can be done by converting the sampling area into a
grid format and labelling each square on the grid with a number
Then a random number generator is used to pick the sample points
