Question: Is there a time sequence of diatoms colonizing a hard substrate?
Season: All year.
Needed: A stream on the campus; 48 bricks; 24 microscope slides; a microscope, preferably 4 microscopes (compound scope preferred, dissecting microscope okay but not great).
How To Do It: Early in the school year, all 24 slides are set out in the stream bed. They are held in place by pinching one end of slide in between two bricks. Make sure all are immersed well below the water’s surface.
At each of 6 two week intervals thereafter, remove 4 slides from the stream and examine them for diatom species. Draw all the different species you see, and give each a qualitative “commonness index” (C = common, M = moderately frequent, R = rare). At the end, graph the different species against time.
Discussion: Is there a time sequence? Do late arriving diatoms grow over early ones? How would you distinguish a simple seasonal progression of diatoms from an establishment progression, in which some diatoms are always faster colonists than others? Can you think of any analogues to diatom succession, for example in the terrestrial part of your campus or backyard?
101. Some Lichen It Hot
Question: Are lichens sensitive to natural or human induced variation in microhabitat/ microclimate?
Season: All year.
Needed: Several treetrunks scattered over campus (including near the busiest street), preferably trunks of a single tree species. Also, compasses if available, meter sticks definitely.
Background Information: Students go outdoors immediately (no introduction), and have a “lichen race” to find the first incontrovertible lichen growing on treetrunk. At that point, have a brief discussion of lichens—what they represent, how they grow (need lots of sunlight, can tolerate extreme drought but not pollutants). Ask students to predict where they will find the most lichens: On north or south facing sides of trees, near to or far from the busy street. Ask them why they are making those particular predictions.
How To Do It: Then students count the number of lichen colonies as follows. Find a tree that is at least 10 cm in diameter at 1 meter above the ground. Lean a meter stick vertically against the north side of the trunk. Count the number of lichen colonies it intersects. Same for south side. Keep tallies separate (i.e., there is a separate line for each tree trunk, and two entries in each line: north and south). Do this for a number of trees far from the street; repeat for a number of trees as near the street as possible. Try to control for tree species and for other important variables such as the size of the clump in which trees exist (trees in deeper shade will have fewer lichens). This should take about 20 minutes. Then, compare tallies.
Discussion: Do south side counts typically exceed north side counts from the same tree? Why? What’s different between south and north sides? Why? Where’s the sun most of the year? Why? What about if we lived in Australia—where would lichens grow?
Calculate the average number of lichens, south face only (or total per tree) per tree in the far street subsample and in the near street subsample. Do trees growing near the street have more or fewer lichens? Why might this be so? What do streets have on them? Cars. And what do cars produce as they pass by? Baddies. So, if lichens are sensitive to these baddies that cars produced, what about other forms of life, even humans? Sensitive too? Might lichens have a use as an “indicator” of quality of air—that is, might we exploit lichens’ sensitivity to atmospheric pollutants as a guide to good air and bad air? How? Etc.
102. Zoned-Out Dragons
Question: Do different kinds of dragonflies and damselflies occur in different habitat zones, and why might this be so?
Season: Fall (Spring).
Framework: I-3-A-ii; II-8-A.
Needed: A pond, marsh, slow moving sunny creek, or other wetland harboring dragonflies and damselflies of two or more species. Paper, pencil, and clipboards. Sidney W. Dunkle’s Dragonflies and Damselflies of Florida, Bermuda and the Bahamas would be nice.
Background Information: No in classroom introduction. Students go out to the watery site and look for dragonflies and damselflies (see Handbook entry on pages 84-85). Brief talk about life cycle (mate by clasping together, female lays eggs in water by repeatedly dipping her abdomen in, eggs hatch, predatory nymphs grow slowly with moulting between stages, final moult produces the winged adult), food (adults consume small flying insects), territoriality (males of many dragonflies defend mating territories), displays (males of many species display to attract females). Ask students, do you think all dragonflies and damselflies will choose the same microhabitats for their feeding/ breeding/ territorial activities? Why or why not?
How To Do It: Okay, let’s see. Have students decide on microhabitat categories to use (e.g., in a pond, these could be: open water without vegetation, open water with emergent vegetation, pond edge vegetation, vegetation near water’s edge, lawn), and have them agree on a common choice of names for the different kinds of dragonflies and/or damselflies you see.
Then simply have them tally the number of each kind they see in each microhabitat (they will have made up a table). Continue for 20 minutes or however long necessary/ available. Then re assemble and compare results.
Discussion: Generate the “why” questions again. Is there any relation between habitat choice and size of insect? Aggressiveness? Which species seem to use the habitats where the most prey exist? Where the best open water exists? Does presence of perches (on vegetation) have anything to do with this? Etc.
103. Perching Dragons
Question: Does the addition of perches change the habitat use and territorial structure of dragonflies?
Season: Fall (Spring).
Needed: A small pond with open water, and a fairly common species of dragonfly inhabiting same.
How To Do It: Start with students observing dragonflies in light of the following: where they fly, where they land, how they eat, how they interact with other individuals. Do dragonflies appear to be defending territories? Do their territories appear to center on their perches, or are their territories independent of perches?
Then, locate chunks of open perch free water. Note quickly their pattern of use by dragonflies—are they “neutral ground” (actually, neutral water) in-between defended territories or at least in between heavily used areas?
Next, create some perches by placing, in each selected chunk of perch free water, a perch of the same type as that used by the dragonflies naturally (e.g., a grass or reed stem). Now note the pattern of use.
Discussion: Does the addition of perches change the use of the site? Do dragonflies use the site more heavily than previously? Are territories set up? Does this imply that dragonflies, and dragonfly activity, are perch limited? What function do perches serve, anyway—certainly dragonflies can live without them!
Extension: Note that this activity can be made more quantitative if desired: with stopwatches or watches with second hands (in this day and age, watches with digital seconds functions), students could calculate the amount of time, out of 2 minutes or another standard time interval, a given stretch of water had a dragonfly in it. This would be done (a) in a comparison between initially perch free and perch containing stretches of water, then (b) in a before and after comparison of the perch addition experiment described above.
104. Submarine Defense
(to avoid being eaten)
Question: What are the different modes by which aquatic insects avoid being eaten?
Season: All year.
Framework: II-5-A, II-5-B.
Needed: A pond, marsh, creek, stream, whatever nearby. Equipment: anything that can be used as a net or sieve; possibilities include large kitchen strainers, dip nets (but not butterfly nets, they’ll get wrecked), a piece of window screen stapled to two long wooden handles. If available, the large kitchen strainers might work better than anything except genuine official dip nets. Do not use colanders, though. Also Needed: for each 4 6 students, one large rectangular refrigerator dish (available in any discount store or grocery store, if not in students’ parents’ kitchens). You’ll also need a jar, bucket, beaker, or some other clean container to transfer water.
Background Information: No classroom introduction; go straight to a wet place, and have the discussion there. Mention that there are lots of things living in the water (especially the immature stages of all dragonflies, damselflies, stoneflies, mayflies, caddisflies, mosquitos; of many other flies, many beetles, etc.). Mention that underwater, for these insects, is a complex three dimensional habitat of swift water (in a stream), still open water, mud, sand, live vegetation, dead vegetation, stems, rocks (in some areas), spaces under rocks (again, in some areas), etc. Mention that these baby insects have many different life styles; some eat live vegetation, some filter small particles and algae from the water, some eat dead vegetation, and some are predators on the others. Mention that there are other predators, too, that eat the baby insects. What? Ask students. The main ones are fishes, of course, but crayfish, some birds (herons, egrets here; dippers in the mountains of the western U.S.), and even mammals (some shrews) also prey on the insects. So, what traits of baby insects might help them to avoid being eaten? Let’s see.
How To Do It: In general, you’ll scoop through the water with your scooper; dump all contents (which will, presumably, include many insects) in the refrigerator dish; add enough water to create at least 2 cm depth; let things settle for a minute or two; and then watch, prodding different parts of the pan occasionally to see if you can stimulate movement. If you’re sampling from a still body of water (pond, marsh, etc.), then you’ll scoop actively (move the scoop—that is, the strainer or dip net—rapidly to prevent fast swimmers from escaping).
If you’re sampling from a relatively swift moving stream, then the best method is to hold the strainer or dip net vertically with the net or strainer part pointing downstream; make sure rim is resting on bottom; and then, with your other hand, agitate the substrate immediately upstream from the scoop, for at least half a minute. Insects will be dislodged and will float into the scoop.
In your sample, you might see the following: Active swimmers (these are either predators themselves, or else fairly large and fast moving individuals that rely on speed to escape predation); scuttlers (insects that rely on a quick dash from one “home base” to another); wrigglers (insects or, more likely, non insect invertebrates such as worms) that simply squirm vulnerably (these are often hidden within the mud); clingers (insects that cling fiercely to plant stems or other secure sites); sprawlers (relatively flattened, sprawling insects that sprawl on the surface of rocks or leaves); crawlers (slow moving but constantly moving insects that crawl among small rocks or within piles of vegetation); and “turtles” (turtle shaped insects with tough exteriors, often predators themselves but also difficult for other predators to eat).
Discussion: Look for behavioral differences. Look for morphological differences associated with the behaviors. What kinds of habitat do you think each kind lives in? How does each behavior, or behavior + morphology, enable the insect to escape, at least sometimes, from predation? Why don’t they all converge on a single “best way” of escaping predation? What could you compare them with—for example, if you dropped in a bunch of housefly larvae or earthworms, which do not normally encounter aquatic predators, which do you think would get eaten first, the introduced insects or those that normally live in the water and exhibit the behaviors you’re investigating? Why? Etc. etc.
105. Why Is Who Where Under Water?
Question: What underwater microhabitats have the most kinds of insects, and why might this be so?
Season: All year.
Needed: Any aquatic site (pond, marsh, creek, stream, whatever, nearby).
Equipment: anything that can be used as a net or sieve; possibilities include large kitchen strainers, dip nets (but not butterfly nets), a piece of window screen stapled to two long wooden handles. If available, the large kitchen strainers might work better than anything except genuine official dip nets. Do not use colanders, though. Also needed for each 4 6 students, one large rectangular refrigerator dish (available in any discount store or grocery store, if not in students’ parents’ kitchens). You’ll also need a jar, bucket, beaker, or some other clean container to transfer water.
How To Do It: Students select two or more very distinctive microhabitats and sample from same. In each microhabitat, they tally the number of different kinds of insects and discuss the different body forms that these entail. For example: a pond or small slow stream with water hyacinth, emergent grasses near the edge, and some open water or muddy bottom would be great.
Using the scooper (strainer, dipnet, etc.), scoop up some water hyacinths and dump them in the refrigerator dish (with additional water); carefully examine the roots for the myriad arthropods (many non insects included) therein. Scoop through the emergent vegetation, and do the same. Do the same in open water (you’ll probably find nothing there). Do the same in muddy bottom.
Discussion: Discuss the role of habitat complexity in determining the number of different kinds of animals that would live there. Why are more complex habitats (e.g., water hyacinth roots) richer in species than structurally simple habitats (such as open water)? How many different kinds of things can an animal do in a complex habitat versus a simple habitat? If there are many different animals available, each doing something slightly different (in terms of searching for food, ability to avoid predation, etc.), won’t a complex habitat automatically accumulate more of these? How do body forms and behaviors of typical animals change with the kind of habitat? Etc. etc. So, what is going to be richer in total number of species: an aquatic area (pond or stream) that only has one kind of microhabitat (say, all water hyacinth), or an aquatic area that has many different kinds of microhabitats? That is, consider two different levels of the hierarchy: the local level (what we are actually examining here), or the number of species within a single microhabitat; and the number of different microhabitats existing within a site. Isn’t the total number of kinds of animals (and plants) a result of both? Etc. etc.
106. Clover Clones
Question: Do clover leaf patterns correspond to lawn microhabit?
Season: All year.
Framework: I2a, I2b.
Necessities: Paper, pencil and clipboard.
How To Do It: Look at the leaves of common Dutch clover in the lawn. Different patches have different markings on the leaves. Typically, about 5-20
“In my early childhood, the best thing about being a budding naturalist was that you got to kill things and inspect them close up. I know that the indiscriminate application of this practice is frowned upon today, since the rare snaffular grossbeak that one shoots and prepares for a museum collection is liable to be the last of its species. But back in those profligate days, when nature was still in flower, if one wished to understand better the marvels of life on earth, one went out and harvested living things by abrogating their life expectancies with an abrupt application of extreme prejudice.”
• John T. Nichols What Is a Naturalist, Anyway? Natural History, November 1992, Vol. 101, No. 11, page 6.