B4.2.1: Biodiversity
Sampling
Sampling: taking measurements of a limited no. of individual organisms present in a particular area
Can use to...
- estimate no. of organisms in an area (don’t have to count them all!)
[__ + abundance (no. of individuals of a species in an area)
- measure a particular characteristic of an organism
[__ use results of the sample to make generalisations or estimates
How sampling is used in measuring the biodiversity of a habitat and the importance of sampling
There are 2 methods of sampling: random + non-random
Random sampling
→ each member of the population is equally likely to be included - selecting individuals by chance
→ used to select a sample that is unbiased
→ can use random number tables or computers (random number generator) to decide which organism to study
[__ taking random samples of an area → use pairs of numbers as x and y coordinates
Could use meter ruler markings or grid references
Non-random sampling
→ sample is NOT chosen at random
3 main non-random sampling techniques:
1. Opportunistic
- Uses organisms that are conveniently available (‘convenience sampling’)
- May not be representative of the population - weakest/least accurate form of sampling
2. Stratified
- Some populations can be divided into strata (sub-groups) based on a particular characteristic eg. male/female
- sex
- Take random sample from each strata, proportional to the strata size
3. Systematic
- Identify different areas w/in an overall habitat + then sample these areas separately
- Used where study includes an environmental gradient - often carried out using a transect (line or belt)
The importance of sampling the range of organisms in a habitat
Reliability of samples
- A sample is never entirely representative of the organisms present in a habitat - TIB:
- Sampling bias - selection process may be biased (accidentally or deliberately). Can reduce effects by using
random sampling → removes human involvement in choosing samples
- Chance - organisms selected may, by chance, not be representative of the whole population. Cannot ever
completely remove chance from the sampling process but can minimise its effect by using a large sample
size (greater no. of individuals studied → lower probability chance will influence the result → more reliable
result)
, Practical investigations collecting random and non-random samples in the field
Techniques to include: use of sweeping nets, pitfall traps, pooters, Tullgren funnel and kick sampling for collecting
different samples.
Sampling animals - techniques for collecting
1. A pooter
→ Used to catch small insects
2. Sweep nets
- Used to catch insects in areas of long grass
3. Pitfall traps
→ Used to catch small, crawling invertebrates eg. beetles, spiders, slugs - fall into hole
- Hole dug in ground deep enough so insects that fall in cannot crawl out
- Hole is covered w/ roof-structure (eg. glass perspex cover) propped above ground so tha insects can crawl in
but the trap doesn’t fill w/ rainwater
- Traps usually left overnight - nocturnal species are sampled too
4. Tree beating
→ Used to catch invertebrates living in a tree / bush
- Large white cloth stretched out under tree → tree is shaken / beaten to dislodge the invertebrates → fall onto
the sheet → collected + studied
5. Kick sampling
→ Used to catch organisms living in a river
- River bank + bed is ‘kicked’ for period of time to disturb the substrate → net is held just downstream for
period of time → captures any organisms released into the flowing water
with due ethical considerations (e.g. pooters, traps, mark-recapture, the ACFOR scale)
Sampling plants
- Normally use a quadrat
[__ should be used after a random sampling technique in order to collect the mpst valid representative sample of an
area
(Quadrats can also be used to pinpoint area where the sample should be collected)
2 main types of quadrat:
1. Point quadrat
- Frame containing a horizontal bar. At (10) set intervals along the bar, long pins can be pushed through the
bar to reach the ground → record each plant species the pin touches
Sampling
Sampling: taking measurements of a limited no. of individual organisms present in a particular area
Can use to...
- estimate no. of organisms in an area (don’t have to count them all!)
[__ + abundance (no. of individuals of a species in an area)
- measure a particular characteristic of an organism
[__ use results of the sample to make generalisations or estimates
How sampling is used in measuring the biodiversity of a habitat and the importance of sampling
There are 2 methods of sampling: random + non-random
Random sampling
→ each member of the population is equally likely to be included - selecting individuals by chance
→ used to select a sample that is unbiased
→ can use random number tables or computers (random number generator) to decide which organism to study
[__ taking random samples of an area → use pairs of numbers as x and y coordinates
Could use meter ruler markings or grid references
Non-random sampling
→ sample is NOT chosen at random
3 main non-random sampling techniques:
1. Opportunistic
- Uses organisms that are conveniently available (‘convenience sampling’)
- May not be representative of the population - weakest/least accurate form of sampling
2. Stratified
- Some populations can be divided into strata (sub-groups) based on a particular characteristic eg. male/female
- sex
- Take random sample from each strata, proportional to the strata size
3. Systematic
- Identify different areas w/in an overall habitat + then sample these areas separately
- Used where study includes an environmental gradient - often carried out using a transect (line or belt)
The importance of sampling the range of organisms in a habitat
Reliability of samples
- A sample is never entirely representative of the organisms present in a habitat - TIB:
- Sampling bias - selection process may be biased (accidentally or deliberately). Can reduce effects by using
random sampling → removes human involvement in choosing samples
- Chance - organisms selected may, by chance, not be representative of the whole population. Cannot ever
completely remove chance from the sampling process but can minimise its effect by using a large sample
size (greater no. of individuals studied → lower probability chance will influence the result → more reliable
result)
, Practical investigations collecting random and non-random samples in the field
Techniques to include: use of sweeping nets, pitfall traps, pooters, Tullgren funnel and kick sampling for collecting
different samples.
Sampling animals - techniques for collecting
1. A pooter
→ Used to catch small insects
2. Sweep nets
- Used to catch insects in areas of long grass
3. Pitfall traps
→ Used to catch small, crawling invertebrates eg. beetles, spiders, slugs - fall into hole
- Hole dug in ground deep enough so insects that fall in cannot crawl out
- Hole is covered w/ roof-structure (eg. glass perspex cover) propped above ground so tha insects can crawl in
but the trap doesn’t fill w/ rainwater
- Traps usually left overnight - nocturnal species are sampled too
4. Tree beating
→ Used to catch invertebrates living in a tree / bush
- Large white cloth stretched out under tree → tree is shaken / beaten to dislodge the invertebrates → fall onto
the sheet → collected + studied
5. Kick sampling
→ Used to catch organisms living in a river
- River bank + bed is ‘kicked’ for period of time to disturb the substrate → net is held just downstream for
period of time → captures any organisms released into the flowing water
with due ethical considerations (e.g. pooters, traps, mark-recapture, the ACFOR scale)
Sampling plants
- Normally use a quadrat
[__ should be used after a random sampling technique in order to collect the mpst valid representative sample of an
area
(Quadrats can also be used to pinpoint area where the sample should be collected)
2 main types of quadrat:
1. Point quadrat
- Frame containing a horizontal bar. At (10) set intervals along the bar, long pins can be pushed through the
bar to reach the ground → record each plant species the pin touches
