12 Practical 1

Investigating the distribution of plants along an environmental gradient, using a transect

Safety Take normal precautions when carrying out fieldwork.

Apparatus and materials • 20 m measuring tape (or length suitable for area of study) • point quadrat • plant keys or identification sheets

Introduction A transect is a systematic sampling method, used to study the distribution of organisms across an environmental gradient, where there is a change from one habitat to another. An example of an environmental gradient is the change from a fully terrestrial habitat, such as a field, to an aquatic one, such as a pond. Here the habitat gradually changes, passing through an intermediate marshy area. Another example is across a path, where the habitat changes from grass to a trampled area and back to grass again. A very clear environmental gradient is on a rocky seashore, where the environment changes from marine at the bottom of the shore, to terrestrial at the top. In between these two extremes, the rocky shore organisms live in habitats with different degrees of immersion. In this practical, you will: • use point quadrats to sample plant species across a terrestrial area.

Procedure 1 Select a suitable area for investigation, and place the measuring tape across the area. 2 Insert the point quadrat in the ground at the start of the tape, at right angles to the tape. 3 Drop a pin through the first hole in the point quadrat. Record any plant species that the pin touches, using a suitable table. For each pin drop, record only one hit per species, regardless of the number of times a pin touches that species. 4 Place the pin in the second hole and repeat step 3. Repeat this procedure until all ten holes have been used. For each species, you will have a maximum of ten hits. 5 Move the quadrat further along the tape, to the next sampling station. (The distance will depend on the size of the sampling area to be investigated.) 6 Repeat steps 2 to 5 at regular intervals along the tape. 7 Combine your results with those of other groups, in order to obtain a bigger sample size. 8 Present the group results graphically, to show the distribution of representative species across the transect. You can do this as series of histograms, or as kite diagrams. Your teacher will help you with this.

COAS Biology 2 Teacher Resources Original material © Cambridge University Press 2009 1 9 a Describe any change in the plant community along the environmental gradient. b Can you explain any trends that are apparent? What biotic or abiotic factors might be important in affecting the distribution of plants across the transect? (See Biology 2, pages 190–1.) c What are the advantages and disadvantages of using a point quadrat, rather than an area (frame) quadrat, when carrying out a transect? d What are the limitations of an ecological investigation of this kind? How could you improve the reliability of your sampling? If time is available, you could measure one of the factors you have identified in b to find out if there is a correlation between the factor and the distribution of plant species. Correlations can be tested statistically, using the Spearman rank correlation coefficient (consult your teacher).

COAS Biology 2 Teacher Resources Original material © Cambridge University Press 2009 2