L2 - sampling

• Sampling:

  -can be used to make an estimate of the biodiversity in an area

  -involves measuring biodiversity in multiple small areas within a habitat and using this information to represent the habitat as a whole

  -it can be used to measure distribution and abundance
• Distribution: where organisms live within a habitat
• Abundance: how many organisms are present
• In order to be truly representative a sample must be large enough to eliminate the effects of chance, i.e. missing a species simply because it didn’t happen to occur at the sample sites assessed. The more samples collected, the more likely it is that the data will be representative of the habitat
• Sampling methods can be:

  -random

  -non random
• Random sampling:

  -sampling sites are selected at random; avoiding bias that might result from a researcher choosing the sites to assess

  -used when a sampling area is reasonably uniform or has no clear pattern of species distribution
• Random sampling process:

  -grid system set up by laying out two long tape measures along the outer edges of a habitat

  -a random number generator is used to generate two random numbers

  -numbers are used like graph coordinates and the sample site is placed at the point of intersection
• Non random sampling:

  -random sampling is not always possible, or may not yield the type of results required so non random sampling may be more appropriate

  -there are three main types; opportunistic, stratified, and systematic
• Opportunistic sampling:

  -sampling decisions based on prior knowledge

  -may deliberately select areas that contain a particular species

  -sampling is carried out on the basis of opportunity, eg. sample sites that can be reach quickly and safely are chosen
• Stratified sampling:

  -the number of random samples taken within each habitat type is proportional to the area covered by each habitat
• Systematic sampling:

  -samples are taken across a habitat with reference to the changes in habitat conditions

  -examples of when samples sites may be taken include; at increasing altitude, distance from woodland edge, distance from shoreline

  -often involves the use of transects
• Advantages of random sampling:

  -avoids bias
• Disadvantages of random sampling:

  -may not cover all habitat areas equally

  -species with low presence may be missed

  -may underestimate biodiversity
• Advantages of opportunistic sampling:

  -easier and quicker than other methods
• Disadvantages of opportunistic sampling:

  -data may be biased

  -large or colourful species may attract researcher

  -may lead to overestimated biodiversity
• Advantages of stratified sampling:

  -ensures all different areas are sampled

  -species are less likely to be missed
• Disadvantages of stratified sampling:

  -may lead to overrepresentation of some areas

  -large numbers of samples taken in small areas that may look different
• Advantages of systematic sampling:

  -useful when habitats show a clear gradient in an environmental factor (eg. drier away from a pond)
• Disadvantages of systematic sampling:

  -only the species in the line or in the belt my be sampled
• Quadrats:

  -suitable for sampling plants or slow moving animals

  -can be different sizes depending on the species being studied

  -may be placed randomly or along a transect
• Measurements within a quadrat might include:

  -number of species present

  -number of individuals of a species present

  -presence/absence of a species

  -percentage cover of a specie

  -abundance of a species using the ACFOR scales
• ACFOR scales:

  -abundant

  -common

  -frequent

  -occasional

  -rare

  -none
• Transects:

  -line along which samples can be taken

  -used during systematic sampling to assess abundance and distribution of organisms affected by changes in abiotic factors across a habitat

  -transect lines are laid out across a habitat along the gradient being investigated
• Types of transect:

  -line

  -belt
• Line transect:

  -lay out a measuring tape in a straight line across the sample area

  -at regular distances along the tape. eg, every metre record the organisms that touch the line
• Belt transect:

  -lay out a measuring tape in a straight line across the sample area

  -place quadrats at regular intervals or continuously along the tape and record the abundance or percentage cover of each species within the quadrat
• Sampling animals:

  -animals are not easy to spot and harder to count

  -large animals will detect humans and hide

  -small animals may also hide and move too quickly to count
• Animal sampling methods:

  -sweeping nets

  -pitfall traps

  -pooters
• Sweeping nets:

  -large, strong nets made from a material with very small holes

  -nets can be swept across vegetation to catch flying insects and insects that live on leaves

  -after sampling the insects in the net can be counted and identified
• Pitfall traps:

  -cans or jars that are sunk into the ground

  -ground dwelling invertebrates fall into the trap as they walk along the ground, and then cannot climb out again

  -a lid ensures the trap does not fill with rain water
• Pooters:

  -small plastic or glass containers with two tubes extending from the lid

  -tubes can be used to suck up small invertebrates

  -first tube is placed over the insect and the second is used by the scientist to create suction

  -once inside the container, the sampled organisms can be viewed and identified