Testing the Moisture Preferences of Isopods

Hypothesis: Isopods prefer environments with higher levels of moisture.

Prediction: If isopods do in fact prefer wetter environments, they will spend significantly more time in the 300 ml (and then the next most in 150 ml) environment than the dry environment.

Methods and Materials: We filled a large plastic rectangle container with 2 inches of sand. The space was physically partitioned into thirds, each about 5.5in x 3.5in. Into each section were poured different amounts of water- 300ml, 150ml, and 0ml, in that respective sequence. This created a respective gradient which we described as saturated, wet, and dry.

A total of 6 isopods were released into the container in the middle (150ml) section of the container and then allotted 30 seconds to orient themselves within their new environment. Then, we observed and recorded how much time each individual spent in each of the 3 sections for 60 seconds. (For ease of observation, only 3 isopods were released at a time, and each person in our group monitored a specific individual for the whole 60 seconds). The statistical test we used to compare the time spent in each category was the Kruskal-Wallace test.

Results: The calculated H-value was 6.75. For a 6-6-6 test, our result was found to be significant (>5.80). We are able to conclude that isopods do in fact prefer wetter environments. While the most collective time wettest environment (300ml), we were surprised to see that the second highest amount of time was spent in the dry (0ml), not the 150ml section as we would have expected.

graph-enviro-vs-time

 

 

Figure 1: Cumulative Time Spent by Isopods in Each Environment, 0 ml (dry), 150 ml (wet), and 300 ml (saturated).

 

Moisture Level (ml)

0 ml R 150 ml
R 300 ml
R
time (s) 0 17 0 17 34 4
42 3 2 15 26 6.5
20 8 17 9.5 10 11
17 9.5 26 6.5 32 5
0 17 8 12.5 60 1
4 14 8 12.5 54 2
R1= 68.5 R2= 73 R3= 29.5

Figure 2. Time Isopods Spent in Each Environment with Ranks and calculated R values

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3 thoughts on “Testing the Moisture Preferences of Isopods

  1. Remember that a hypothesis is more general, and a prediction is specific and follows from the hypothesis if it is true. Predictions have the if/then format and often suggest an experiment. (You should reverse your subheadings and make your prediction even more specific to what you actually tested). Also – think about a way to present your data in a more analyzed way (like a graph of means w/se bars).

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