Question: What plant traits enhance or deter grasshopper feeding?
Note: This is similar to 58 and 59, but broader in that it uses a generalist herbivore, the grasshopper. The comparisons and ideas can be expanded far beyond the sample here.
How To Do It: Begin by students catching a number of late nymphs or adults of one of our medium sized to larger grasshopper species (lubber grasshoppers are ideal, although they might scare students). Insect nets, even (especially) home-made ones, are great fun here. Grasshoppers are kept in large Mason jars, or the ubiquitous clear plastic not-Ziploc freezer bags. They are simply given choice between two different kinds of fodder, and either directly or indirectly (by looking the next morning) the students determine which of the fodders is preferred.
Discussion: Then they speculate why. Of course, the reasons for making each comparison are given beforehand—and students should be encouraged to make up their own comparison. Suggested comparisons follow:
a) “Rough” sandpapery grass versus “soft smooth” grass. Although grasshopppers are true to their name, their mandibles can still be abraded by the numerous silica (glass) particles in some grasses. Thus, which one would you expect them to prefer?
Old vs. young leaves of, for example, goldenrod, or practically anything else.
American holly leaves (the prickly Christmas ones, very common locally) intact, versus same with edge + prickles carefully removed with a sharp scissors.
Leaves from evergreen oaks (e.g., live oak) vs. deciduous oaks (e.g., turkey oak, water oak). Which would you expect to have the better protection against herbivory, thus the lesser attraction for a grasshopper?
Leaves from “nectary plants” (e.g., Cassia fasciculata, some Vicia species) versus similar-looking leaves from non-nectary plants (e.g., other small legume species). Would you expect the plants whose foliage is protected by ants to have greater or lesser chemical protection than plants whose foliage is not protected by ants?
Normal- versus strongly-smelling leaves.
Collard greens or broccoli leaves (not florets) versus Romaine lettuce. Which leaves have “mustard oils” in them? What might be the function of mustard oils?
Bits of lettuce leaf plain, or “painted” with squeezed juice from various other plants thought to have noxious qualities. Can grasshoppers taste? smell? and many others.
Season: F (late S may be O.K. in many years).
67. A Bad Tea Party
Question: Do oak leaves have any substances in them that might serve to deter herbivores, and how can you tell?
Season: S, F (W).
Note: This might not work; I haven’t tried it yet—but if it does, it’s a great activity. Try it yourselves—it’ll take only a few minutes.
Needed: Two times as many tea bells as there are oak species in the schoolyard, boiling water, two times as many porcelain teacups as there are oak species in the schoolyard, milk.
Background: Tannins are naturally occurring chemicals that used to be used (still are) to tan animal hides and make leather. They occur in many plants, especially in oaks. So what? Well, what does the milk show you? Tannins glom up proteins and make them unavailable for digestion.
How To Do It: Students collect living oak leaves from whatever species exist in the schoolyard (most schoolyards have at least 1 species). In those species where this is possible, both young and old leaves should be collected, and kept separate. A tea is made from each age/species combination. To make tea: choose an approximately equal number, or better, volume of leaves from each age/species combination. Shred leaves and pack into teabell. Make “oak tea” by pouring an equal amount of water over each tea bell in each cup. Label cups. Wait exactly 5 minutes. Take out tea bells. What color is the water? Arrange cups in order from lightest to darkest. Look and see what order you’ve put the cups in; write it down. Finally, drop a teaspooonful of milk into each cup (this is the part that needs to be pre-tested). Anything happen? [if this works as it should, at least the darker cups, with more tannins, should curdle the milk as the tannins bind with milk proteins.] OK, now look at the order in which you’ve put the cups. So, what’s the dark stuff? It’s tannins.
Discussion: So, who will get a better diet, a plant muncher feeding on a plant without tannins or one feeding on a plant with tannins? Guess. Now, what order have you put the cups in? What leaves have the fewest tannins? the most? are there any consistent differences? do young leaves have more or fewer tannins than old leaves? if you were a leaf muncher, which leaves would you choose (here we are again!)? Now, look at the way in which you’ve arranged the species. Which species have the most tannins? the least? Any other features of the oaks you can associate with tannin content? Are those with evergreen leaves more loaded with tannins? This is all beginning to overlap quite a bit, isn’t it? oh well. When would be the best time of year to be a caterpillar feeding on oak leaves? the worst? all sorts of other questions possible.
68. Fire Ants: Fiends or Friends?
Question: Do fire ants keep munchers off plants, and what are the implications?
Note: This is another one that must be tested—but it should take all of 10 minutes to test it (I’ve never done it).
Needed: Fire ant colonies in the schoolyard (most may have been poisoned out, but surely there are some fire ants around!).
How To Do It: The easiest thing to do would be to count plant-munchers on plants within, say, 50 cm of fire ant mounds, and at least 10 m from the nearest fire ant mound, assuming that more or less equivalent vegetation could be found in both sites. Slightly more time consuming would be to construct some “quadrat frames” from sticks, pipe cleaners, or whatever, about 20 x 20 cm, and to count numbers of plant-munchers in quadrats located 20 cm from fire ant mound and 10 m from fire ant mound. Ideally one would design a “potted plant experiment,” in which potted plants with heavy induced herbivore loads would be moved into the field, some near fire ant mounds and some distant; but this would be beyond the reach of most elementary school classrooms.
Alternative: The possibility of this working would be enhanced greatly if sugar water were squirted or dripped over the sample plants or areas (both those close to, and those far from, fire ant colonies). Wny? [in fact, one of the ants-as-crop-pesticides schemes includes aerial spraying of crops with sugar water].
Discussion: What are we trying to do here? Why should ants go onto foliage of plants? What are they seeking? Do plants benefit, then, from being near fire ants? Might the dreaded and despised fire ant play a potentially useful role in agriculture? How versatile would fire ants be in comparison to chemical insecticides? Etc. etc.
Season: F, S.
9. Catch a Leprechaun, Find a Pot of Gold
Question: What goes on on a nectary plant—who comes to nectaries, and what do they do there? (Herbivores are the Leprechauns, the extra-floral-nectary is the pot of gold.)
Note: This is a special version of activity #2, concentrating especially on action at the extra-floral nectaries, and any other actions the nectary visitors might take while on the foliage (i.e., do ants coming to foliage remove or consume herbivores, or their eggs, in passing?). See #2 for ideas.
How To Do It: Students sit and watch either vetch or Cassia fasciculata, depending on the time of year and the schoolyard, for a few minutes, documenting the nectary action and formulating testable questions about it. Early morning (around 9-10 AM) is best.
Season: early F (Cassia), early S (Vicia).
70. Ant Plants
Question: Does the presence of extra-floral nectaries simply serve to concentrate ants on the plants in question, increasing the chance of encounter between ant and herbivore egg/larva?
Season: same as in #69.
Background Information: In the EFN plants we have, there’s really nothing too highly specialized about the relationship between EFNs and ants: there’s not a particular ant species, for example, that hangs out around EFN-plants and vigorously defends the plant. Rather, the plant just “puts out” EFNs in “hopes” of attracting and concentrating ants (and wasps) that just might happen to remove herbivores or their eggs in passing. But don’t tell the students this—yet.
How To Do It: IF EFN plants (either Cassia fasculata or a vetch with EFNs) exist in the schoolyards, then students simply census ants per unit of leaf area (estimated, crudely if necessary) and compare those censuses with censuses done on nearby non-EFN plants. This should be done for at least 10 cases, and the numbers compared. Also, if the plants are scattered widely over the area, it would be interesting to compare the ants—are the same ants always there, or do the ant species vary from spot to spot?
71. Sluggish Squirrels
Question: Do botflies slow down a squirrel, and what might the consequences be?
Background Information: In some years many local squirrels are infested with botflies.
How To Do It: If the schoolyard contains many relatively tame squirrels, send students out squirrel-watching. Each time a squirrel is located, count the number of lumps on it. Each lump is a developing botfly larva. Note the physical condition of the squirrel: F for fat, M for medium, S for skinny. Note the activity of the squirrel: A for normally active, S for slow, VS for very slow and stumbly.
Discussion: Is there an association between number of botflies and either physical condition or activity level? What might be the consequences? Might skinny squirrels starve to death? Might VS squirrels fall easy prey to predators, or simply be unable to travel to food sources? In any event, are heavy parasite loads harmful to the host? If a squirrel with many botflies starves or is eaten by a predator, what happens to the botflies? Boy, botflies are dumb—even tiny plant lice or other insects (see activities above) can avoid becoming so clumped that they put a strain on their resources. But in order to discover why botflies are so dumb, students should find out about botfly life cycles—female botflies don’t lay eggs directly on squirrels, rather on mosquitoes that bite squirrels, so that female botflies have no control over the distribution of their eggs. Anyway, there should be lots of questions students can be led to ask here—it’s just too late at night for me to think of them.
72. What Birds Leave Behind
Question: What do bird droppings have in them, and what’s the significance to plants?
Season: F, W (especially when robins & waxwings are around).
Framework: 6a (3bi).
Background Information: See Handbook pages ***. Birds rarely defecate on the wing—frugivorous bats in the tropics usually defecate on the wing—leading to very different distributions of the seeds they release.
How To Do It: Students search through vegetation under trees, beneath hedges, along edge of woods, in fact anywhere birds might perch, looking for bird droppings on foliage or on ground. When bird droppings are found, students examine carefully (teasing apart with pencil if possible) and look for seeds. When seeds are found, students try to identify them by looking at seeds in fleshy fruits around schoolyard.
Discussion: What’s going on here? Are birds seed slayers? or are they acting as good seed dispersers? how far away are seeds from the plants that produced them? are the seeds in good condition, and how would you test this? are the seeds surrounded by a ready mix of fertilizer? what is the effect of birds’ fruit consumption on the distribution of plants in the next generation? where are most plants with bird-dispersed seeds likely to be located in the next generation—under places where birds can sit, or out in the open (i.e., do birds take dumps sitting down or in flight?
Are bird-dispersed plants likely to be good colonists of abandoned pastures without trees? how might you increase the colonization rate of plants with flesh fruits? how about putting out perches for birds, or leaving dead snags? what would the effect on plant diversity and distribution be if birds were extinguished? where do the fruit-eating birds come from—aren’t many of them migrants? even if we protect birds here, what if the places they migrate to/from lack such protection? etc. etc. lots of questions here, all based on little mounds of fecal matter. This works.
73. Seed Movers and Shakers
Question: Are birds or mammals responsible for seed removal in the schoolyard?
Framework: 6a (4c, 5d).
Needed: a bag of sunflower birdseed; five disposable aluminum turkey baking pans (the kind in all the supermarkets at holiday time) with a half-circle cut out of each end.
Background Information: Note that many animals that take seeds (or fruits) may act simultaneously as seed predators and seed dispersers: the seeds they actually eat are, of course, destroyed, but they may bury some seeds for later use (and forget them) or else drop seeds in transit, thus inadvertently acting as perfectly good seed dispersers. Both small mammals (mice) and seed-eating birds (doves, sparrows, towhees, cardinals, etc. etc.) may act in these two fashions.
How To Do It: At each of five different points around the shrubbiest edges of the schoolyard (i.e., the least civilized parts), put out a little pile of 25 sunflower seeds, exposed; 1 meter away, make another pile of seeds, but this time put the aluminum pan over the pile. The exposed pile is accessible to birds and mammals, the enclosed pile to mammals only. Check the next day and count seeds remaining (hopefully, neither will they all still be there nor will they all be removed regardless of situation).
Discussion: So, who moves seeds? Discuss the possible fate of seeds. Are there any plants in the schoolyard whose seeds tend to pile up? relate the experimental results to these natural plant populations.
74. Location, Location, Location
Question: Does the efficacy of seed removal vary with habitat, and why might this be so?
Framework: 6a (5d, 4c, 11).
Note: Same as #73, but here there’s an additional wrinkle: do the experiment in at least 2 different habitats, say the open schoolyard, a weedy unmowed area, a shrubby border, the edge of a woods, at the base of large oak trees, etc.
Discussion: Does it seem as if mice are more prevalent in some places than others? birds? why might this be so? what characteristics of the different habitats do you think are responsible? in what habitats are few or no seeds moved? what might be the consequences to natural plant populations in the different habitats? are there both negative and positive consequences to the absence of seed movers (see discussion in #73)?
75. Flood the Market, or Grand Opening Sale?
Question: How does the rate at which fruits are taken by birds vary with the number of fruits on the plant?
Season: late S (for elderberry and a few other species); FW (depending on species chosen—see fruits entry in field guide).
Framework: 6a (4d, 3bi).
Needed: a bird-visited fruiting plant population in which number of fruits varies greatly among individuals. Possibilities: beauty berry (fall), dogwood (fall), holly or dahoon (fall/winter), elderberry (end of school year), many others depending on the school.
How To Do It: As fruits in the population begin to ripen, count the total number of fruits on each plant. Then monitor at least twice a week (more often if possible), at least until 50% of the total fruits in the population have been removed, preferably until 90% of the total fruits in the population have been removed. This will take just a small amount of time each session. At the end of the monitoring session, note (a) the total number of fruit removed per plant, or the per-plant removal; (b) the per cent of fruit removed, or the per-fruit removal. Of course, during this interval (probably several weeks) hopefully you will have seen who is removing the fruit—i.e., a bird.
Discussion: So, does either type of removal vary with the crop size? What bird traits might be responsible? If there’s plenty of food around, might birds ignore plants with only a few fruits, instead remaining in plants with plenty easily available? On the other hand, might not birds in a large plant become satiated, so that the total number of fruits removed from a large plant may be great but the per-fruit removal actually may be lower than for a medium-sized plant? What is “optimal crop size” for a plant? What’s most important to a plant’s reproductive success, and contribution to the next generation: the total number of seeds it disperses (presumably indicated by the total number of fruit removed), or its efficiency (the fraction of fruits produced that are removed, or fraction of seeds produced that are dispersed)? Why don’t all plants exert themselves to produce as many fruits as possible? What else might be attracted to extremely large crop sizes (parasites!)? If a lot of fruits are sitting there, aren’t birds likely to remain perched in the trees? so where will their feces land? will the seeds really have been dispersed far? etc. etc.—a lot can be discussed based on the results, or even based on the ongoing monitoring before final result are in, and students should always be asked “and how would you test that?”.
76. In the flesh: Fruit Traits.
Question: How do seed size and number vary with fruit size?
How To Do It: Start with a “fruit hunt,” collecting ripe fleshy fruits from as many species as can be found on school grounds. Measure diameter with mm ruler. Then open the fruits, count the numbers of seeds, and measure the long axis of the seeds. Compare results.
Discussion: Questions to consider: Who eats the fruits? How big are their mouths? All else equal, which plant would leave more offspring: one with many seeds per fruit, or one with only one seed per fruit? So, why don’t fruits with big seeds also have lots of them? What limits the total seed mass in a fruit? That is, why is there a “tradeoff” between size and number of seeds? Besides the size of a bird’s mouth, what else might set a limit on the total mass of seeds in a fruit? Does a plant have an infinite amount of energy and resources to put into the seeds in each fruit? And what if there were huge energy-filled packets in each fruit—who else might be attracted? Ever hear of putting all your eggs in one basket? Incidentally, does there seem to be an upper limit on the size of our local wild fruits? Do some fruits that grow near the ground seem to be much bigger than those on shrubs, vines, and trees? How might you explain this? Do other things besides birds eat fruits and possibly disperse seeds? What might these be? Opossums, racoons, foxes, and possibly even gopher tortoises? How would you investigate this? Are the large fruits colored differently from the small ones found on shrubs, trees, vines? Do they have a different consistency? Are the seeds smaller or larger? Back to the bird fruits: do you think that all seeds are swallowed by birds? What about the really big seeds? Might a bird upchuck these seeds rather than swallow them? Would dispersal still occur? Why wouldn’t the bird swallow them? What if the bird had its gut full of undigestible, heavy seeds—would there be any room left for food? and might not the bird have trouble flying? Might not birds selectively eat fruits with a high pulp-to-seed ratio? How might this affect traits in plants? If you were to examine a bird’s (say, a robin’s) treatment of a whole range of fruits, might you not see fruits with many small seeds swallowed whole, and the seeds excreted, but the seed upchucked in fruits with a single large seed? What might the differences be in the distribution patterns of the seeds after dispersal? etc. etc. etc. Many questions here, based on the simple observation of natural animal-consumed fruits.
Season: F, W (S).
Framework: 6a (4d, 3bi).
Question: How are different flower-visiting animals distributed among the various fall flowering Compositae? Pollinator patterns on daisies and their relatives.
Framework: 6b (3ai).
Note: This is #35 made much more specific.
Background Information: In most “waste places” (old fields, schoolyard edges, etc.) from September-November, several species of the daisy family, (Asteraceae or Compositae), flower simultaneously. Many have the typical “daisy shape” of ray and disc flowers; many others have disc flowers only. Size of florets ranges from miniscule (especially in those with ray and disc flowers) to at least 1 cm long (in Liatris etc.). Colors vary from white, white/yellow, yellow through deep purple, violet, and blue. Inflorescence structure varies greatly.
How To Do It: Send students roaming around the schoolyard, looking for any plant in the daisy family (yes, even Spanish-needle & goldenrod) and writing down the kinds of insects visiting the flowers. For each kind of flower, write down whether it has both disc (“head”) and ray (“petal”) flowers, or disc flowers only; the approximate length of the disc flowers; the flower color(s); the number of composite heads or “flowers” on the plant; the size of the plant. See #35 for details on what to do next.
Discussion: What kinds of flowers do butterflies seem to prefer? Do different butterflies go to different kinds? Do bees and butterflies go to the same kinds of flowers? What about beetles—where are they? etc. etc. But focus questions on the fact that these are all related plants, that share many characteristics but have diverged greatly, in some cases, in flower traits and in the kinds of animals that visit them.
78. Mushroom Mania