TOPICS: Invertebrates, classification, ecology
LEVEL: Middle or high school
TIME: One to three class periods.
ADVANCE PREPARATION: Order pitfall traps in early autumn from a biological supply company, or start collecting yogurt and sour cream containers (16 oz size) to make your own traps. The outer cups of the traps must be set into the ground before the ground freezes (STEP A). You may wish to do the autumn preparation (STEP A) and the initial winter preparations (STEPS B-D) yourself to save class time
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MATERIALS:
Mix equal parts automobile antifreeze (ethylene glycol) with water. Cover the pitfall traps with scrap lumber or old shingles about 30 cm square. Stakes should be long enough to be seen over expected snow depth
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PREDICTIONS:
In class discussion, encourage creative, logical, and critical thinking. We recommend that you introduce the following ideas if they are not suggested by students: Snow insulates the ground from daily temperature fluctuations and wind. Under deep snow, the ground may remain unfrozen all winter. Invertebrates are ectotherms or "cold-blooded animals" which do not regulate their body temperature metabolically
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STEP A.
Set pitfall traps in areas away from human activity. Use several traps placed in a lawn area as a control group. You may wish to place pitfall traps in other habitats (such as under shrubs, deciduous trees, conifers, or in an old field), or change the snow cover over some lawn pitfall traps (remove or compact the snow as it falls). Placing a pitfall trap under a cross country or snowmobile trail may be interesting
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STEP E:
Take a flat pan or box outside to hold student samples for safe-keeping
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STEP H:
Older or more advanced students could be asked to identify all invertebrates in the sample, and compare locations not only by total numbers, but also by diversity (number of different invertebrate types).
QUESTIONS 4-8 require higher-order thinking skills. We recommend that you discuss these questions with your class before having students write out their answers
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2.
Answers will vary
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3.
Expect more invertebrates in a forest or field than in lawn, but school lawn may be more diverse than manicured shrub areas
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4.
Locations with diverse plant life generally can support diverse animal life
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5.
Yes. In general, more invertebrate activity will be found under a deep insulating snow layer
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6.
Snow is an insulator, perhaps keeping soil temperatures above freezing all winter. Snow also protects the animals underneath from the wind and moderates temperature fluctuations
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7.
Compacting should reduce the insulation value of the snow, and compress the leaf litter. The resulting temperatures and reduced space should decrease invertebrate activity, perhaps reducing their survival
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8.
Invertebrates eat organic debris, fungi, and other soil invertebrates. See Table 1 in Teacher Background.