Sampling

A quadrat is a sqaure frame used for studying ecosystems. 

• It is used to study the abundance and distribution of different plant species
• Some plants are difficult to count as individuals so percentage cover is used instead

Some precautions must be taken:

• Randomly position the quadrats across the habitat, using random numbers to plot coordinates.
• You need your sample size to be large enough. Ecologists create a cumulative frequency table. When the graph levels off, you know that your sample size is large enough.

Population size of a species = 

Mean number of individuals of the species in each quadrat 

 ÷

Fraction of the total habitat area covered by a quadrat

• These help you to look more systematically for changes in vegetation in a habitat.
• A transect is a line taken across the habitat.
• This line is usually created using a tape measure.
•  Samples are taken at random intervals.

There are two approaches to taking a transect:

• Line transect - at regular intervals, take note of the species touching the tape measure.
• Belt transect - at regular intervals, place a quadrat next to the line or move the quadrat along the line to get a more accurate representation of the habitat.