Discussion: Do galls come in different shapes and sizes? Are some inhabited, some not? Why are there so many different kinds? Are there any kinds of galls that occur on more than one kind of plant, or not? If not, why not? Might different kinds of plants be different enough that the same insects couldn’t use them, or the insects’ gall forming technique wouldn’t work? If you have more than one kind of gall on a single plant, why? Is one kind of gall restricted to a special place on the plant, another kind to another place? Why might this be so?
Look at the tissues in the different parts of the plant that harbor galls. Are some places tougher than others, greener than others, bigger than others? How come the galls aren’t very crowded together? What’s the most you find on a single leaf or a single stem, for example? Why aren’t they more crowded? Why don’t you find a hundred galls on a single leaf? What if there were 99 galls already on a leaf and you, a female about to lay eggs, came along and had a choice between that leaf and a leaf with 0 galls? Think about it. Any evidence for parasitism or predation on gall insects? How might you tell? And so forth.
29. Loving Lynx Spiders
Question: Why do mother green lynx spiders guard their eggs?
Framework: I-3-B-ii (II-5-B).
Season: Fall only (September to October or so).
Notes: This requires a reasonably large patch of “old field vegetation,” i.e., goldenrod (Solidago), Monarda mint, horseweed (Conyza canadensis), prairie feather (Liatris), deer’s tongue or vanilla plant (Carphephorus), Elephant’s foot (Elephantopus), or other tall Fall weeds. This might also require more than one session.
Background Information: See Handbook, page 58.
How To Do It: First, search the weeds for green lynx spiders. These are on the underside of flower heads or the underside of the upper bunches of leaves, usually about two feet off the ground.
Then spend a couple of minutes observing. What’s the spider doing? What’s that leathery looking ball under it? Hey, those might be eggs! Okay, so when will they hatch? How will they make it through the winter? If the mother wasn’t there, what might happen to those eggs? What happens when you poke the egg sac with a piece of grass? Does the spider respond? What if you were an insect about to eat the eggs, for example a parasitic wasp? Might eggs whose mothers guard them stand a better chance of turning into new spiders than might motherless eggs? How might you test this?
Now for the hard part. If the students are successful in locating at least 6 or 8 lynx spiders guarding eggs, then have them select half of these (how selected? on one side of the field? Or random? Why?) and leave as “unmanipulated controls.” Mark the stem of each with a bit of colored string, flagging tape, or something so that the spider can be located again. Then mark the other 50% of the spider stems, using a different color of thread/tape or whatever. On this latter half, gently nudge Mother Lynx Spider from her egg mass into a jar or yogurt container (see below). Release Mother at the most distant point on the campus grounds (but in nice vegetation).
Okay, one week later (or each week thereafter), check to see whether motherless egg sacs have survived as well as mothered ones. So, does a mother’s love enhance the success of spider eggs?
30. Reaching for the Sky
Question: How does the array of plant growth forms vary with habitat, and why?
Season: Spring, Fall (Winter).
Framework: I-3-C-i (I-1).
Background Information: Start with a brief discussion. Plants need sunlight to make their food. Where does the sunlight come from? From the sun in the sky, of course, dummy. So, what if there’s another plant in the way, blocking the sunlight? Two main outcomes: A plant could make less food and thus grow more slowly; or a plant could grow taller than the shader, so that its exposed to full sunlight again. But what does growing taller entail? A big stem (or trunk). Does a stem or trunk produce food too? Relative to the leaves, almost never anything. So the trunk uses up a lot of the food that might have gone into making flowers and seeds and other wonderful things. Another possible outcome: Cheat and grow taller not by making a strong stem, but by clambering over the tops of other plants that have strong stems. What’s this? A vine! The point is, no “solution” to the light problem is perfect, but one “solution” might work best in one habitat, another in a different habitat.
How To Do It: Explore different habitats around the school grounds, noting not only the array of growth forms within each, but also the relative commonness of growth forms. Count the number of kinds of plants or individual plants that possess each growth form. Explain any differences in these numbers between habitats. After a brief introduction, send students out to “explore” at least two different habitats on campus. For example,
(a) the least well mowed part of the campus proper (or, if the school is lucky enough to have it, a patch of “old field” vegetation or other weedy vegetation);
(b) if it exists, a woods edge or at least a hedge.
Look for different plant growth forms. In each different habitat, record how many plant “growth forms” you find out of the five basic kinds (herb, shrub, tree, vine, epiphyte).
Discussion: In the weedy area, how many plant “growth forms” can you find out of the five basic kinds? Why so many herbs? Are they able to reach for the sky okay? Look at the “understory” of the weeds—are the shorter weeds skimpier and scrawnier looking? Why? Are there herb “trees” too? Do herbs differ among themselves in the amount of material they put into stems (to grow taller) versus leaves or flowers? Can you find any tree or shrub seedlings among the herbs? What do you think might happen after a long time without mowing?
Now, consider the hedge or forest edge. How many growth forms now? Do the herbs look any different (scrawnier, for example) than those out in the open? Do you see any vines? How are they “reaching for the sky”? What about shrubs—how do shrubs make it? Do you think they grow as fast as the trees that shade them? But then again, do they “bother” putting as much material into the trunk? Do you see any “epiphytes” on the tree limbs? Are they successful in “reaching for the sky”? My, my, doesn’t it seem as if epiphytes have the best of both worlds—all that sunlight with no need to use “food” for a stem? But what about water and nutrients? Don’t plants need those too? How do epiphytes get them? With great difficulty! Okay, so maybe being an epiphyte isn’t so great after all.
Extension: If time remains (ha!), students can “predict” the kinds of growth forms they might find in other habitats, for example a tropical rain forest or the Arctic or a desert or a swamp, or a place that has a lot of lightning strikes.
Question: Are plants that grow in different light habitats constructed differently?
Season: Spring, Fall (Winter in some places with evergreen plants).
Framework: I-3-C-i (III-13).
Needed: This requires some shrubs or saplings growing in shade (under a forest canopy) and some growing in full sunlight.
Background Information: To start, students have a look at one shrub or sapling growing in the shade and one growing in full sunlight. Are there any differences?
In which one are the leaves arranged in a single sparse “layer” or a few widely spaced “layers?” In which are leaves tightly packed, either haphazardly or in many tightly packed layers? In which are there few leaves per branch, with little overlap between leaves relative to light coming from above, versus many leaves packed in along the branch with considerable overlap among them?
How might the differences between shade and sun architecture be related to the light regime under which these two plants live? Where is light more scarce? Where is it abundant?
How To Do It: After looking at both examples and discussing the possible relationship to light, students predict which kind of shrub will be found to be most prevalent under the shade of forest canopy, and which kind they will find most prevalent under full sunlight. Let students come up with justifications for their predictions. Then set them loose, tallying the frequency of each type they find in each habitat.
Discussion: Do the results match the predictions? Why or why not?
32. Toughing it out in the Florida Sun
Question: Are “sun leaves” tougher than “shade leaves,” and why might this be so?
Season: Fall (Spring, Winter).
Notes: The best trees to use are Water oak (Quercus nigra). Other possible trees include laurel oak (Quercus laurifolia or Quercus hemisphaerica), swamp chestnut oak (Quercus michauxii), and hickory (Carya).
Needed: Leaf Tough-O-Meter made from a styrofoam cup, string, sharp pencil, paper clips, paper puncher, and water as follows.
To make a Leaf Tough o meter: make a bucket out of a styrofoam cup by drilling two holes through the rim and passing a string through. Tie either end, on outside of hole, to a paper clip to hold. Now, to middle of “bucket handle” tie one end of another string, about 25 centimeters (1 foot) long. To the other end of the second string, tie a small paper clip. This is the official Tough o Meter.
Background Information: Why should there be any difference in “toughness” between sun and shade leaves?
Well, what do leaves do? They make plant food from sunlight. Even thin leaves, though, have layers of cells full of green chloroplasts, the tiny food factories. A leaf in full sun can have lots of layers of chloroplasts, because there’s plenty of light to penetrate even to the undermost layer of cells. What about leaves in shade? If there were lots of layers of chloroplasts, then the lowermost might be in the dark. They would be worthless blobs of jelly. So, where would expect the thicker, and therefore tougher leaves to be found?
Another reason is water. Which leaves are likely to dry out more quickly, sun or shade leaves? Why? So, wouldn’t sun leaves be expected to have some protection against losing their water, like waxy layers?
So, one might predict that leaves in the sun would be tougher than leaves in the shade. The students should have some basis for making a prediction before going out and picking leaves.
How To Do It: Find a tree that has some leaves exposed to full sunlight for most of the day, and others that are in partial to full shade throughout the day. If your campus or backyard has a woodsy edge, a tree on the edge would be perfect. One side would be in the sun, the other in the shade. Otherwise, one could use inner and outside leaves from an isolated tree on the school grounds.
Okay, each student picks 10 shade leaves and 10 sun leaves of about the same age and size. No fair picking new leaves for shade leaves!
To measure toughness, use Leaf Tough o meters.
Figure 2. Tough-O-Meter.
To test leaf toughness: Take a hand paper punch and punch a hole in the exact center of the leaf. This will involve
punching the hole through the midrib
as well. Pass the paper clip at the
end of the Tough-O-Meter cord
through the punched out hole,
and then position the paper
clip flat along the leaf
surface, perpendicular to the
midrib, so that the string drops from the middle of it
through the hole.
holds the leaf horizontally by
either end. The other student
slowly pours water into the
styrofoam cup (note that this
will be done outside!).
How much water can be poured before the leaf rips and the Tough O Meter splashes to the ground? According to the prediction, to get the sun leaves to rip, more water must be poured into the Tough o Meter than for the shade leaves.
33. The Language of Flowers
Question: Do butterflies prefer to forage at some lantana flowers but not others, and why?
Season: Spring (Fall, Winter).
Framework: I-3-C-ii (II-6-A, I-3-A-i).
Needed: This requires some Lantana camara on the school grounds. Many have it, at least near the parking lot. See the Handbook entry on Lantana. Small paper lunch bags.
How To Do It: The afternoon before the exercise, either teacher or selected students place a small paper lunch bag over a few flowering heads of lantana. The purpose of this will become obvious later.
The activity begins by having students look at Lantana flower heads and observing that there are two colors of flowers, brighter lighter colored flowers at the center surrounded by a ring of darker colored ones. Have students count the approximate number of flowers of each color, on each of several heads.
Then, sit and watch a butterfly foraging. Not every student has to have a unique butterfly foraging at her or his flowers; one butterfly will do for all. Where does the butterfly land? Which flowers does it probe? Count the number of “bright” flowers probed versus the number of “dark” flowers. Which does the butterfly select?
Come to a conclusion, then speculate on why. Try plucking a few bright flowers (carefully) and sucking nectar from the bottom. Any nectar? Do the same with a few flowers from the outer dark ring. Any nectar? Probably there will be no discernible nectar in either.
Now for the lunchbagged plants. Remove lunchbags and do the same trick: pluck carefully and suck out nectar, if any, from both kinds of flowers. What’s the result? Why, then, would a butterfly select one kind over the other? So, why are the “old dark” flowers kept on the plant? Perhaps a target so the butterfly can spot it from a long ways away? How might you test this? Tune in tomorrow for another activity asking that question.
Discussion: Meanwhile: comparing the results from non lunchbagged versus lunchbagged flowers, can you now explain butterflies’ foraging preferences? Why couldn’t you tell by trying to suck nectar from the open flowers? Is a butterfly’s ability to detect a food reward, and to make use of that food, better than yours? What does this say about the whole idea of “perception?”
34. Educated Bees
Question: Do bees choose from among flowers of different kinds, or do they slurp from everything?
Season: Spring, Fall.
Framework: I-3-C-ii (II-6-B, I-3-A-i).
Needed: An area on the campus with several kinds of flowering plants such as clover (Trifolium repens), alfalfa (Medicago sativa), wild radish (Raphanus sativus), Richardia, most any kind of mint family flowers (Stachys, Monarda, Salvia, Scutellaria, Hyptis, Lamium…), Spanish Needles (Bidens), etc. would be fine. A tally sheet and pencil, or a map, meter stick, and colored pencils (see below).
How To Do It: Find an area on campus with several different kinds of herbs, weeds, and/or lawn weeds flowering . First, have students “scan” the flowers to see what kinds of bees are visiting them. Honeybees and bumblebees will be the two chief visitors, with honeybees probably predominating. But let the students discover this.
Next, have the students make up a “tally sheet” of flower kinds versus bee kinds (and see activity 35). That is, have a row for each of the (probably two, at this level of discrimination) bee kinds, and a column for each different common flower kind. Have the students search for five minutes. Each time the student sees a bee on a flower, s/he simply makes a tally mark in the appropriate category.
Next (the core of the activity), have each student follow an individual bee for as long as possible, up to five minutes. If there is time, which will be the case if students lose track of an individual bee, then the student starts with a new individual.
Tally as before, except now each new row represents a different bee individual, and there is a tally for each time the bee leaves one individual plant and goes to another. That is, if the bee is on a clover head and goes to another clover head, there is a tally mark under “clover,” but if the bee leaves a clover head and goes to a wild radish there is a tally under “wild radish.” It’s not necessary to know the names of the different plants, only that they are different. They could be “Flower 1,” “Flower 2,” etc.
IF there are any bumblebees or other non honeybees foraging, make sure that at least a couple of students try to follow these too. If at all possible, don’t let everyone follow the ubiquitous honeybees.
Discussion: So, do honeybees as a group forage broadly over available flowers? Or do they pile up on certain kinds only? Any idea why some flower kinds may be more bee popular than others? How would you investigate this? What about bumblebees? Are they quite widely distributed over the available flowers?
Compare the results from following individuals to the earlier results for each bee kind as a whole. Do individual bees, whether honey or bumble , stick to only one or a few flower kinds? Do different individuals have different “specialties?” Why might this bee so? Did you notice that bees feeding on certain flowers used complicated techniques and maneuvers in order to extract the nectar/pollen? Is it possible that it takes some practice (just like the piano) to learn the best way to get food from a certain kind of flower? Might this be why individuals tend to stick to one kind of flower or another?
Further Discussion: How would you investigate this possible reason for “majoring” and “minoring” by individual bees? So, why do different bees of the same kind have different specialties (if they do)? Any explanation?
Imagine you are a bumblebee just emerging from the nest (“hive”) for the first time. You are “green,” with no practice getting nectar or pollen from any kind of flower. Most flower kinds are already being used by your nestmates! So there is hardly any nectar in the flowers that they are already visiting. Luckily, a new kind of flower is just coming into bloom, and no one else has discovered it yet, because they’re busy with the old kinds. These new flowers have lots of nectar! If you bumbled around from one flower kind to another, at which kind would you most likely discover a reward? Might this not encourage you to learn the most efficient way to get at that reward?
Here is a slightly different version of this activity. It’s especially useful for bumblebees, but also works for honeybees (although, since they’re an exotic species, it’s less biologically realistic). Have each student make a map of a small area (say, 1 square meter) that contains at least two flower kinds. Trace the route of different individual bees through this area, using a different colored pencil for each different individual bee. From these maps, is there any evidence for “majoring” and “minoring” on the part of bee individuals? Now refer to the questions above.
Final Discussion: Think of the plant’s perspective for a bit. Which is more beneficial to the plants, in terms of pollination:
(a) Being visited by a kind of animal in which each individual is quite non selective, getting nectar and pollen from several different kinds of flowers; or
(b) Being visited by a kind of animal in which the animals as a whole are quite non selective, using many flower kinds, but in which individuals stick mainly to one kind of flower at a time?
How might you investigate this?
35. Different Strokes for Different Folks
Question: Do different kinds of animals choose different kinds of flowers to visit? If so, are there any “flower traits” or particular characteristics associated with these choices?
Season: Fall, Spring.
Framework: I-3-C-ii (I-3-A-i, II-6-B).
Background Information: See the Handbook, pages 12-13 and 30-34.
How To Do It, Part One: Begin with a short “scan” over all floriferous areas, noting briefly what kinds of animals are visiting flowers and how they are getting food from the flower. Probably the main flower visitors will be bees (of all kinds), butterflies, and wasps, with perhaps some beetles and flies thrown in.
Watch the different insects eating. Butterflies use a long thin “tongue” to extract nectar; while honeybees and bumblebees use a much shorter “tongue.” Most small bees and flies have scarcely any “tongue”; and wasps andbeetles have none at all, except for syrphid flies, which have a medium-length tongue.
Spend no more than 5 6 minutes, if possible, on the scan; then assemble for a brief talk about “perception.”
Different insects have different color vision: Bees and wasps see red/orange colors very poorly; butterflies see those colors very well. Beetles perceive light colors well, such as yellow, cream, and white, but see dark colors poorly.
Regarding food perception: Would a short tongued bee “perceive” that there was nectar at the bottom of a deep tubed flower? Would a long tongued butterfly “perceive” that there was nectar at the base of a complicated flower that takes a bee’s brute force to open?
How To Do It, Part Two: Have students make up a chart of “flower kind” versus “visitor kind.” Under each flower kind, they should also note some characteristics of the flower including color, odor or fragrance, size, and shape. For shape, note things such as: Is it a long tube or short tube? a brush with or without petals? dish or bowl shaped? With a three dimensional “gullet”—like most mint flowers? And so forth.
Students run around tallying what kind of visitors are visiting which kind of flowers.
Discussion: At the end, get together, compare notes, and through discussion come to a conclusion. Are flower visitors all mixed up, or are they “partitioned” among different plant kinds? Do the flowers that attract butterflies also attract bees? beetles? flies? Are there some kinds of flowers that seem to attract everyone? Why? Now, are there any traits in common among the different flower kinds used by a given animal kind? What are these traits? Can you explain why that particular kind of animal might be responding to those particular traits? How would you investigate this? And so forth.
36. How Sweet It Is!