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Unformatted text preview: Exercise 5B Behavior & Population Dispersion
Parts of this lab adapted from General Ecology Labs, Dr. Chris Brown, Tennessee Technological University and Ecology on
Campus, Dr. Robert Kingsolver, Bellarmine University. Lab Exercise 5B: Dispersion of Isopods in an Artificial Habitat
Research Question Preparation Figure 3.5 Slice potatoes and insert pins to make isopod shelters. Materials (per laboratory team) Biology 6C 111 Procedure
1. Prepare "resource islands" from potatoes. First, cross-section a potato with parallel cuts evenly
apart. You should get four or five round sections from each potato. Discard the
ends, and cut more potatoes until you have 20 sections of approximately equal size and
thickness. Then insert three map pins in a triangle formation on the bottom of each potato
slice, so that the potato slice will stand on the map pins like a three-legged stool (Figure 3.5).
The pins should leave about
of space for the isopods to crawl underneath.
2. Arrange the 20 potato slices, pinheads down, in the bottom of the sweater box. Distribute the
potato slices uniformly, with space separating each one. You now have an artificial habitat with
20 resource islands suitable for isopod colonization.
3. Release 20-30 isopods into the box. Take a few minutes to observe their behavior. How do
they react to the box edges? to the potato "islands"? to one another?
4. Leave the isopods overnight. The underside of the potato slice islands provide a dark, humid
microclimate that is preferred by isopods. They also feed on the potatoes. If lights are left on in
the room, all isopods should select one of the potato slices to hide under.
5. After the isopods have had time to adjust to their habitat (12-48 hrs), count the number of
isopods underneath each potato slice. You will need to pick up each "habitat island," because
the isopods often invert themselves and cling to the potato. Record 0 if there are none in that
sample. The 20 numbers you record should sum to the number of isopods you released into
6. Complete the Data Table and calculation page at the end of this chapter. The mean number of
isopods per potato slice x is the ecological density, and the variance/mean ratio provides an
index of aggregation for the captive isopod population. Data Analysis
2 S 2 x
By comparing the variance of your 20 potato islands with the mean, you will determine whether
the plants you sampled are aggregated, random, or uniformly dispersed. 112 Exercise 5.B. Behavioral Ecology Table 3.2 Potato Islands Biology 6C 113 Discussion
1. Based on the variance/mean ratio, what can you conclude about the spatial pattern of your
population? How might you explain this pattern, given observations you made as you were
sampling? 2. Would you expect another organism from the same biological community to exhibit a similar
index of dispersion? Is spatial pattern a property of the organism, or of its habitat? 114 Exercise 5.B. Behavioral Ecology ...
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