Sampling Flashcards
What is sampling?
taking measurements of a limited number of individual organisms present in a particular area
What is sampling used for?
used to estimate the number of organisms in an area without having to count them all
What is the number of individuals present in an area known as?
the abundance of an organism
How can sampling be used to measure a characteristic?
e.g. height
you cannot measure all plants, you can measure some and take an average
What is random sampling?
selecting individuals by chance
each individual has an equal chance of selection
How is random sampling done?
1) mark out a grid on the grass using two tape measures laid at right angles
2) use random numbers to determine the x coordinate and y
3) take a sample at each of the coordinate pairs generated
What is opportunistic non-random sampling?
may not be representative of the population - weakest
uses organisms that are conveniently available
What is stratified non-random sampling?
populations can be divided into a number of strata based on characteristics
e.g. male and female
a random sample is then taken from each of these strata proportionate to its size
What is systematic non-random sampling??
often uses a line or a belt transect
line transect - marking a line between poles, describes organisms which touch the line or distances of samples from the line - used to show how distribtuion changes
belt transect- two parallel lines are marked and samples are taken of the area between the two lines
How is there a sampling bias?
selection process may be biased
may choose to sample a area that has more flowers because it looks interesting
can be reduced using random sampling
How are the results affected by chance? How can this be minimised
there is a chance there may be more or fewer plants in a area by chance, not representative of the whole population
minimised using large sample size
What are often the limitations
biased - not representative
too few samples take - not valied
misidentification/msicount - not accurate
distribtuion and abundance changes over time
