11.2 Types Of Smapling Flashcards
What is sampling
Sampling means taking measurements of a limited number of individual organisms present in a particular area
What can sampling be used for
Used to estimate the number of organisms in an area without having to count them all
Used to measure a particular characteristic of an organism
What is the abundance of an organism .
The number of individuals of a species present in an area
Random sampling
Means selecting individuals by chance
They each have a equal likelihood of selection
How would u take a random sample at a grass verge
Mark out a grid in the grass using two tape measure laid at right angles
Use random number to determine x and y coordinate on grid
Take a sample at each of the coordinate pairs generated
Non random sampling
Sample is to chosen out rando and can be divided into tree techniques
Opportunistic
Stratified
Systematic
Opportunistic sampling
Weakest form of sampling as it may not be representative of population
Uses organisms that are conveniently available
Stratified sampling
Populations divided into group of strata based on particular characteristics random sample then taken from each others these strata proportional to size
Systematic sampling
Different areas within an overall habitat are identified which then sampled separately
It is often carried out using a line or belt transect
Describe a line and belt transect
Line transect - marking a line along the group between two poles and taking samples at specific points
Eg describing all organisms which touch the line
Belt transect - provides more info as tow parallel lines are marked sample taken of the area between two lines
Reasons why sample is never reliable or entirely representative
Sampling bias - selection process may be biased
Chance - organisms selected may not be representative of whole population. It can be minimised by using large sample size
