11.3 Sampling Techniques

Question 1

Sampling animals

Answer 1

Sampling animals needs to be quick and efficient so as not to harm them so you can use these techniques:

1) a pooter is used to catch small insects. By sucking through a mouthpiece, insects are drawn into the holding chamber via the inlet tube. A filter before the mouthpiece prevents them entering the mouth.
2) sweep nets are used to catch insects in areas of long grass.
3) pitfall traps are used to catch small, crawling invertebrates like beetles, spiders and slugs.

A hole is dug in the ground which insects fall into. It’s covered with a roof structure propped above so the trap doesn’t fill with rainwater. These are usually left overnight so nocturnal animals can be sampled too.

Question 2

Sampling Animals - Pooters

Answer 2

1. A pooter can be used to capture little insects; you suck them up through a mouthpiece covered by a filter, into an inlet tube and then the holding chamber.

Question 3

SA - Sweep Nets

Answer 3

2. Sweep nets are used to catch insects in areas of long grass.

Question 4

SA - Tree Beating

Answer 4

4. Tree beating is used to take samples of the invertebrates living in a tree or bush. A large white cloth is stretched out under the tree while the tree is shaken and beaten to dislodge the invertebrates; they fall into the cloth to be studied.

Question 5

SA - Pitfall Traps

Answer 5

3. Pitfall traps used to catch small, crawling invertebrates like beetles, slugs and spiders. It’s a deep hole in the ground covered with a roof-structure so it doesn’t fill with rainwater; can be left overnight so nocturnal animals can be sampled as well.

Question 6

SA - Kick sampling

Answer 6

5. Kick sampling used to study organisms in a river; river bank/bed is ‘kicked’ to disturb the substrate; net is held downstream for a set period of time to capture any organisms released into the flowing water.

Question 7

Sampling Plants - quadrats

Answer 7

Usually use a quadrat which can pinpoint an area in which the sample of plants should be collected.

2 types:
1. point quadrat - frame with a horizontal bar. At set intervals along the bar, long pins can be pushed through to reach the ground. Each species of plant the pin touches is recorded.

2. frame quadrat - square frame divided into a grid of equal sections; type and number of species within each section of the quadrat is recorded.

To collect more valid representative sample of an area, quadrats should be used following a random sampling technique.

To study distribution of organisms, quadrats can be placed systematically along a line or belt transect.

Question 8

Measuring Species richness

Answer 8

Should use a combination of quadrat techniques to identify all species in a habitat. A list should be compiled of each species identified; total number of species can then be calculated.

To enable scientists to identify organisms accurately, identification keys are often used. May contain images or questions which classify them into a category of species.

Question 9

Measuring Species evenness

Answer 9

Using frame quadrats:

Density - if single large plants can be easily seen, count how many there are every 1m by 1m square quadrat = density per square metre.

Frequency - when individuals are hard to count like grass or moss. Using the small quadrat grids, count the number of squares of a particular species is present in.

Percentage cover - used for speed as lots of data can be collected quickly. Useful when particular species is abundant or difficult to count.

Question 10

Estimating Animal popn. size

Answer 10

capture-mark-release-recapture method. Allows the animals the redistribute themselves.

Question 11

Measuring abiotic factors

Answer 11

Non-living conditions in a habitat. They have a direct effect on the living organisms that reside there. E.g. water and light available.

Many abiotic factors can be measured quickly using a range of sensors which are good because:

1. rapid changes can be detected
2. human error is eliminated
3. high degree of precision is achieved
4. data can be stored and tracked

To enable them to draw conclusions, they measure these conditions at every sampling point.

For example:
factor sensor used example measurement
wind speed anemometer m s ^-1
light intensity light meter lx
relative humidity humidity sensor mg dm^-3
pH pH probe pH
temp. temp. probe degrees C
O2 content in H20 dissolved O2 probe mg dm^-3