Topic 5

Random sampling is useful to estimate the population of different species in a habitat that is generally similar across the habitat. By sampling random areas of the habitat we can estimate the population of each species without having to count all individuals in the entire habitat which would be very difficult to achieve.

To select random areas to sample we can create coordinates using the measuring tapes…

…use one of the long measuring tapes to mark out an ‘x-axis’ for our coordinates…

…and place the other measuring tapes to mark out a ‘y-axis’ for our coordinates.

Use two random numbers to identify the coordinates to sample…

…the first should be the ‘x-axis’ coordinate, the second the ‘y-axis’ coordinate.

Carefully place the quadrat in the position identified by the coordinates. Measure and record the different species inside the quadrat:

Species with clearly identifiable individuals can simply be counted, recording the total number of individuals in the quadrat.

Species such as grass that are difficult to identify individual organisms you can estimate the total coverage of the quadrat – this is much easier using quadrats divided into smaller squares, e.g. 5x 5 squares, as each small square can be estimated to the nearest quarter (e.g. 3 quarters) and these totalled to give a percentage out of 100.

Record all the different species in your results table for the quadrat.

Repeat this process at least 9 more times to collect at least 10 sets of data, each from randomly generated coordinates in the marked habitat.

Systematic sampling is useful to show changes in the population of different species in a habitat that may be due to changing conditions across the habitat, such as the time exposed to air and submerged in water by changing tides. By sampling areas of the habitat along a line (transect) e.g. from low to high tide levels, we can measure changes in the distribution of different species along the transect.

To measure changes in distribution of different species in the habitat we create a transect…

…use the long measuring tape to mark out a transect…

…decide what type of transect you have time to carry out:

For a continuous belt transect you record the abundance of each species in the quadrat and repeat these readings by moving the quadrat up the line without leaving any gaps between. (This method is best for very short transects and when you have lots of time to record your results).

For an interrupted belt transect you record the abundance along the transect using a quadrat but leave regular spaces between areas sampled with the quadrat – this collects a representative sample of results and can be used for longer distances where you want to indicate the abundance as well as where different species are present.

For a line transact you simply record every species touching the line along its whole length (best for very long transects and when you don’t have a lot of time to record your results).

Starting some time before low tide (ideally at least an hour), place a quadrat next to the transect line and record the abundance of each organism in the quadrat – either by counting the number of individuals, or estimating the percentage cover. Starting before low tide gives you time to get used to recording your results as the tide goes out.

For an interrupted belt transect move the quadrat along the line leaving a gap between where it was previously.

Record the abundance of each species in the quadrat in the second position.

Repeat this process of moving the quadrat along the transect and recording the abundance until low tide, then return to above the point where you started on the transect and continue up the shore until you reach the splash zone. You should try to record results from about 10 quadrats along the transect line.

By recording information about different species and repeating these measurements over several years it is possible to monitor changes in populations …

… such as to monitor for new invasive species that may move into a habitat, or to monitor the spread or increase in invasive species populations to ensure these are not becoming a problem.