Woodlice are small terrestrial crustaceans that feed on organic matter in leaf litter and in the soil. While carrying out an ecological survey in woodland, a student noticed that there seemed to be more woodlice in areas where there was plenty of leaf litter and other organic matter. She also noticed that there appeared to be more leaf litter towards the middle of the wood than at the edge. To find out if there is a relationship between the number of woodlice and the organic content of the soil, she used a line transect. At each point along the transect, she:

• Took a sample of soil.
• Counted the number of woodlice in three separate samples of leaf litter from the surface of the soil.

She took the samples of soil to a laboratory to find out their percentage organic content. Her results are in the table below.

a. i. Explain why the student has taken three samples of woodlice at each point along the transect.

ii. Suggest three further pieces of information you would need if you were to repeat the student’s investigation.

b. Draw a scatter graph to see if there is any relationship between the number of woodlice and the mass of organic matter in the soil.

c. State the null hypothesis for this investigation.

d. Carry out the Spearman’s rank test on the data that you have used to draw the scatter graph.

e. What conclusions can you make? You will need to consult Table P2.8 on page 504 to help you answer this question.

Table P2.8

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Number of woodlice in sample Distance along transect / m Percentage organic matter in the soil 2 3 mean 5.42 10.02 15.56 8.25 9.62 11.73 1 2 0.6 4 3 2.3 8 2 2 2.3 16 1.3 20 7 6. 6.0 9.0 12.3 24 9 28 10.67 8 14 15 32 9.36 14 16 11.6 36 11.35 15.11 12 17 6 11.6 40 17 11.0 20.87 20.30 44 20 2. 10.3 48 20 12 11.0