Sampling

What is sampling

Method of investigating the abundance and distribution of species and populations

Define distribution

Describes how a species is spread throughout an ecosystem

Define abundance

The number of individuals in a species

What are the 4 ways you can measure abundance?

1. Frequency of occurrence
2. Density of species
3. Percentage cover
4. Abundance scales

What is frequency of occurrence

A tick or cross on if the species is present in the quadrat

What is the con of frequency of occurrence

Ignores density of species, focuses on richness

What is density of species

When you count each individual in the quadrat

What is the con of density of species

This is time consuming for small species such as grass

What is percentage cover

Estimating the area covered by the species

What is the con of percentage cover

This is difficult to estimate for when there is overlap

What is an abundance scale

Stating the area is:

* abundant
* common
* frequent
* occasional
* rare

What is the con of abundance scales

subjective

What are the key steps in sampling

1. Select an area to sample (that is a small geographical area within the habitat being studied)
2. Count number of individuals of each species
3. Repeat process, taking a meaningful number of samples
4. Use results to **estimate** total number of individuals

What are the 2 types of sampling

Random and non-ranom

What can quadrats be used to measure

Distribution and abundance of plants and slow-moving animals

Why do quadrats need to be laid randomly

To avoid sampling bias

How can you lay quadrats randomly

Convert sampling area into a graid, label each square with a number and use a random number generator to pick sample points

What are pitfall traps

Cans or jars that are buried in the ground that are used to catch ground-dwelling (often nocturnal) insects and other invertebrates as they fall into the trap

What are sweeping nets

These are large, strong nets with a fine material (very small holes) that are used to catch flying insects and insects that live in long grass by sweeping the net back and forth through the grass

What is a tullgren funnel

These are funnels with a light bulb above and a container below that are used to collect invertebrates that live in leaf litter or soil. The leaf litter or soil is placed in the funnel and the light and heat forces the invertebrates to move down until they drop into the container

What are pooters

These are small plastic or glass containers with two tubes sticking out that are used to suck up small insects and other small invertebrates.

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

What is kick sampling

This technique is used to catch freshwater invertebrates living in streams or rivers.

A net in placed on the stream-bed so that the water is flowing into it and the stream-bed just above the net is churned up by the scientist (using their foot) for a set period of time.

The invertebrates are carried by the stream into the net

How is a line transect used

•Lay out a measuring tape in a straight line across the sample area

•At **equal distances** along the tape, **record the identity of the organisms that touch the line.** For example, every 2m

What kind of data does a line transect produce

Qualitative data

How is a belt transect used

•Place quadrats at **regular intervals** along the tape and **record the abundance or percentage cover of each species within each quadrat**

What kind of data does a belt transect produce

Quantitative data

What are the 3 types of non-random sampling

1. systematic
2. opportunistic
3. stratified

What is the advantage of random sampling

Unbiased data

What are the disadvantages of random sampling

* May not cover all areas
* Species with low presence can be missed
* Can cause an underestimation of biodiversity

How is opportunistic sampling conducted

Researchers make decisions based on prior knowledge on which area to sample

What is the advantage of opportunistic sampling

Easier and faster

What are the disadvantages of opportunistic sampling

Based data

Overestimates are common (because you want the area to be really good for your research so you’re more generous when sampling)

How is stratified sampling conducted

Dividing a habitat into areas which appear different and sampling these different areas

What are the advantages of stratified sampling

* Ensures all different areas are sampled
* Species are not unrepresented

What are the disadvantages of stratified sampling

* Over-representation of some areas in the sample due to appearing different
* Disproportionate number of samples taken in one area (presumably the areas with a lot of species present)

How is systematic sampling conducted

Samples taken at ^^fixed intervals^^ across the habitat.  Line transects and belt transects are examples.

When is systematic sampling ideal

When a clear gradient is visible

Eg; straight pathway from a woodland

What are the disadvantages of systematic sampling

* Only species along the line are recorded


* Some species may be missed


* Underestimate of biodiversity