Can damsefly change the abudance of midge larvae?

INSTRUCTIONS TO CANDIDATES

ANSWER ALL QUESTIONS

1. Can damsefly change the abudance of midge larvae?

We want to assess whether there is a difference in the impact that the predatory larvae of three damselfly species (Enallagma, Lestes and Pyrrhosoma) have on the abundance of midge larvae in a pond. We plan to conduct an experiment in which small (1 m2) nylon mesh cages are set up in the pond. All damselfly larvae will be removed from the cages and each cage will then be stocked with 20 individuals of one of the species. After 3 weeks we will sample the cages and count the density of midge larvae in each. We have 12 cages altogether, so four replicates of each of the three species can be established.

We have two options:

• Use a CRD and distribute the cages at random, or

• Adopt an RCBD by grouping the cages into clusters of three, placing each cluster at a randomly chosen location, and assigning the three species to cages at random within each cluster.

Answer the following two questions.

1. Which design do you think is more reasonable and what else information do you need to justify your choice?

2. If one choose RCBD for this experiment, and collect the data below:

Species Block

A B C D

Enallagma 304 578 680 356

Lestes 464 509 740 390

Pyrrhosoma 320 458 630 350

Analyze the data and provide your interpretation or conclusions.

 

2. Copper Plate Warping

An experiment is conducted to investigate two factors that influence the warping of copper plates. The response was a measure of amount of warping. The two factors are "temperature" and "copper content". Analyse the data and answer the following questions.

Temperature Copper Content

40 60 80 100

50 17,20 16,21 24,22 28,27

75 12,9 18,13 17,12 27,31

100 16,12 18,21 25,23 30,23

125 21,17 23,21 23,22 29,31

 

1. Is there any indication that either factor affects the amount of warping? Is there any interaction between the factors? Use α=0.05.

2. Analyse the residuals from this experiment.

 

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