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IV Bees wax
IV. UNIT FOUR PLANT-ANIMAL INTERACTIONS Objectives: To introduce scrub plants and their adaptations for life in the scrub. To emphasize the importance of plants as producers and their place at the beginning of the food chain. Plant-animal interactions discussed include herbivory, mutualism, plants as providers of shelter, and plant- human interactions. IV.A.1 Palmettos: Old-Timers of the Scrub Part One: Observing and Measuring Palmettos Part Two: Constructing a Palmetto Timeline IV.B.1 Oak Trees: The Serve Yourself Buffet Part One: Collecting the Data Part Two: Making a Collection of Leaf-eating Evidence IV. Plant-Animal Interactions Introduction Placing the plant unit last in a curriculum may seem unusual since plants are so basic to all life in the scrub, just as they are everywhere on our planet. But to consider plants requires moving to new levels of complexity. The earlier activities in this curriculum were stepping- stones to this unit. The simplest aspects of biology deal with physics, as in the physics of sand. Predation, as in ant lions and ants, is still a relatively simple topic, as long as the focus is on the mechanisms of predation and not the population dynamics of predator and prey. Decomposition introduces the idea that there are whole systems revolving around Spider wasp pollinating plant by-products. Now it is possible to consider the much larger palmetto flowers systems of plant-animal interactions. This curriculum has been slowly building increasing levels of complexity. Plants also express the theme of adaptations for life in the scrub in the most definitive and complex ways. Plants cannot move around freely, and must take life as it comes. Plants cannot flee fire in the scrub, so they must have specific adaptations for it. Plants cannot hide from the sun in the heat of the day. They cannot roam around like animals and search for concentrations of nutrients. Although the adaptations of plants for life in the scrub are clearly displayed in leaf and growth forms, some adaptations are difficult for students, or anyone else, to imagine. Therefore, it makes sense to introduce plant adaptations after you and your students have thoroughly explored the concept of adaptation. This section concentrates on two groups of plants that are very important in the Florida scrub habitat--the palmettos and the oaks. Unfortunately, dozens of other groups of plants and their interactions with animals are not mentioned. By developing the stories of palmettos and oaks in depth, we hope to more clearly convey the number of complex relationships in the scrub than if we quickly presented many plants. Observant students will probably notice additional plant-animal relationships. These students can be encouraged to design little research projects to explore these relationships. Since many of the relationships between plants and animals in the scrub have not been studied by scientists, a research project undertaken by a student could easily grow into an exciting original project for a science fair or a school research project. These could even become part of a new curriculum! The examples of pollination ecology mentioned below should give you an idea of all the things that could be studied. At least three species of pawpaws occur in Florida Scrub, including the endangered Four-petal pawpaw, found in scrubs along the East Coast of Florida. Pawpaws bloom in the spring and have big white flowers that are not attractive to bees and butterflies. The flowers produce a peculiar fruity or musky smell that attracts beetles, especially flower scarabs and longhorn beetles. The Lake Placid scrub mint is an endangered plant, which lives only in a small area near the town of Lake Placid. Other kinds of endangered scrub mints occur in other areas of Florida. In order to protect an endangered plant species it can be useful to know some details of its biology. Scientists began looking at the insects pollinating the Lake Placid scrub mint These beetles feed on part of the center and discovered that one kind of bee-fly of the flower and carry pollen from one usually pollinates its flowers. The pollen plant to another. Although these beetles of this plant is kept under pressure fly away quickly when disturbed, you inside the pollen-bearing structures, can easily catch one in a clear plastic called anthers. When the fly collects food storage bag and examine it for a nectar from the flower, the fly’s furry moment before releasing it. (A plastic belly presses down on the top of these bag should be in every naturalist’s field anthers. This pressure causes a little slit kit!) Students can identify the pollen to open in the anther so that the pollen producing flowers by sniffing at each comes popping out onto the fly’s belly. flower (without touching it) for the characteristic fragrance. To catch To save the Lake Placid scrub mint we beetles that may be feeding in the need this fly. Fortunately, the fly is quite flower, place a bag gently over the common. Nobody knows, however, what flower, then tap the flower or move its the fly larvae eat. Most likely, they are inner petals. If beetles are feeding in the predators that attack other insects flower, they will tumble out and buzz underground, but nobody really knows if around the bag like bees or wasps. these fly larvae require something Because these beetles fly and buzz like special. stinging insects but do not sting, they provide a good example of behavioral mimicry. A. PALMETTOS: OLD-TIMERS OF THE SCRUB Introduction Plants that thrive in the Florida scrub are tougher than Indiana Jones in Raiders of the Lost Ark. And like Indiana Jones, it is amazing that plants can survive at all. They must prevent their leaves from drying out in the intense summer heat or from baking under the broiling sunlight. They must be able to survive weeks without water, yet be strong enough to survive a deluge during summer storms. They must grow and thrive with almost no nutrients. When fire approaches, they cannot run away, but must either sprout back after being burned to The Florida scrub-jay the ground or recolonize from seeds that were protected from the collects tan-colored threads flames. Scrub plants must defend themselves against an abundance from scrub palmetto fronds of insect and animal predators and from being overwhelmed by molds at the beginning of nesting and fungus during the wet season. Yet despite all the conditions that season and weaves them seem to work against them, some scrub plants seem to grow with together to make a soft lining great ease. for its oak-twig nest. Palmettos demonstrate some of the water conserving features found in many scrub plants: The leaves are covered with a coating of wax that prevents water from escaping from the surface of the leaf. One reason why Florida scrub burns so fiercely is that the heavy wax coating on palmetto leaves ignites once the leaves are heated sufficiently. The blue tortoise beetle The leaves are tough and thick, and not easily damaged in ways spends its entire life on the that could expose the moist inner tissue. leaves of either a scrub and The leaves are held upright when the plant is growing in open saw palmetto. With its tiny jaws, it scrapes away at the areas, so the rays of the sun hit the flat surfaces of the leaves palmetto leaf, leaving a thin directly during morning and afternoon, but not in the middle of yellowish line behind it as it the day when the sun is hottest. moves along the leaf. When alarmed, the blue tortoise There are other water-saving adaptations in scrub plants. Some of beetle clamps itself down on these are discussed later in the section on oaks. How is a cactus the leaf holding on with its adapted for drought? yellow feet. Each foot is covered with hundreds of oily hairs, which stick to the Background Information wax that covers the palmetto The saw and scrub palmetto are two rugged species found throughout leaf. The larva of the blue the Florida scrub in peninsular Florida. (Scrub palmetto is not found tortoise beetle also feeds on growing in the Panhandle.) These tough, slow-growing plants are well palmetto leaves. It covers adapted to scrub and live very long lives--sometimes as long as 600- itself with curved bits of 700 years! Palmettos play an important role in scrub habitat by waste material so that it providing food and cover for animals and material for nest building. looks like a tiny, upside Because your students are probably very familiar with palmettos, they down bird’s nest. This beetle is never common enough to will have lots of fun discovering so many new things about these damage a palmetto plant. plants. Both species of palmettos bloom during a predictable period, so your class can plan on visiting a few flowering plants to see what kind of insects drop by for nectar! Your students can easily locate and estimate the age of saw palmettos by measuring the length of the stem (or trunk) during Part One of the activity. Both types of palmetto grow slowly out from the bud end and produce between 3 to 7 leaves a year--depending on the type of palmetto. Each leaf can live for 1 to 2 years. When a leaf dies, it loses its color and stays attached to the stem for about a year. Palmetto leaves are covered with a waxy coating which make them highly flammable. Palmetto leaves burn easily, but the growing bud of the saw palmetto is well protected by fiber that covers the stem and thick palm boots (the bases of old fronds). Because the stem is so well protected, it never burns down to the ground. After a palmetto burns, the charred stem can produce a new leaf within a week of the fire. Palmettos are one of the quickest scrub plants to respond after a fire. The Although Florida scrub might stem and growing point of the scrub palmetto are usually under seem too dry for frogs, squirrel the sand and stay protected from fire. tree frogs are quite common. They can find shady places that are cooler and more humid Although palmettos respond quickly after a fire and are difficult among the leaves of plants. to kill, young palmetto seedlings take a long time to get This is another example of a established and mature enough to produce flowers. Saw microhabitat, like the ones in palmettos are clonal, so are more likely to spread the leaf litter discussed in Unit underground than to produce new seedlings from fruits. Most Three. Palmettos are often a populations of saw palmettos are made up of very old, well- good place for tree frogs, established individuals. Saw palmettos grow in dense because the frog can tuck itself impenetrable thickets and can reach heights of 6 to10 feet or down in a folded palmetto leaf more. As the stem grows along the ground, it sends out roots out of sight during the day. Tree to collect moisture from the soil. In moist, shady areas, the frogs eat spiders, crickets, and katydids also found on the stem grows toward the light and is more erect. Scrub palmettos. Some areas near palmettos, on the other hand, are not clonal, so do not grow in scrub habitat are often marshes thickets as saw palmettos do. during the rainy season (summer, fall) and dry during Both kinds of palmettos produce a cluster of white flowers in the dry season (winter, spring). the spring. Saw palmettos typically bloom during March-April Because these seasonal and scrub palmettos during April-May. Some plants will bloom wetlands do not have fish that at other times during the year--usually as a result of a recent eat tadpoles, these marshes fire. During a warm, sunny day, you can find many insect are good places for tree frogs to species as well as a great number of individual insects visiting lay their eggs. the sweet-smelling palmetto flowers. Palmetto berries develop soon after the flowers drop. Initially, the fruit is green. As the fruit slowly ripens, it changes to yellow, then orange, and, finally, turns black by October. The interactions between palmettos and animals are almost endless! Many animals are dependent on palmettos for survival. More than 100 birds, 25 amphibians, 61 reptiles, 27 mammals, and hundreds of insect species use palmettos as food, cover, or for nest material. Black bears, white-tailed deer, raccoons, opossums, gray fox, wild turkeys, bobwhite quail, and gopher tortoises eat palmetto berries. Feral pigs and bear dig out the growing tip from the stem (which kills the plant) and eat the Estimating the Age newest leaves and “heart of palm.” Gopher tortoises and cattle eat parts of a Saw Palmetto of the leaves. Florida scrub-jays, grasshopper sparrows, and wild turkeys collect parts of the plant to use as nesting material. Panther, black bear, Dr. Warren Abrahamson and white-tailed deer use the protected cover provided by palmettos as a of Bucknell University has birthing den. Spiders and wasps commonly build nests and webs in the been conducting fronds and blue tortoise beetles “glue” themselves to the leaves (see research at Archbold page 122). Vines often use palmetto for support and mosses and lichen Biological Station in Lake Placid, Florida, for more grow along the stem if it has not recently burned. than 20 years. He discovered that the age Humans are known to have eaten the palmetto berries in the past, but of a saw palmetto could the berries are said to have a “rancid tobacco juice” flavor. Today, saw be estimated by palmetto berries are used by pharmaceutical companies to manufacture examining the certain drugs and medications. In one season, well over 7,000 tons of relationship between the palmetto berries are harvested. Wildlife researchers worry that if demand growth rate of the for palmetto berries increases, the loss of available berries will be palmetto stem and the harmful to wildlife that eats the berries. stem length. For four years, he measured the growth of more than 400 Saw Palmetto Adaptation Review palmettos in two different Tough leaves provide protection from drought and damage. habitats. The averaged Waxy leaves keep the plant from drying out. growth rates for all Vertically-held leaves in open areas mean less exposure to the palmettos in both habitats noon sun. was 1.2 cm per year. Less vertically-held leaves in shaded sites allow a plant to capture By measuring the length more light. of a saw palmetto stem Fibrous layer in the trunk insulates the plant from fire. and dividing the length by Clonal growth from root system allows the plant to colonize quickly 1.2, the approximate age in open patches after a fire. of any saw palmetto can Blooming after fire means plants can take advantage of nutrients be determined. from ash, and produce more seeds when open areas are Intermediate-sized saw available. palmettos in his study typically had a stem Flowers produce large amounts of nectar which attract many length of 100-150 cm with species of insects for pollination an estimated average Edible fruits attract raccoons and other animals that disperse fruit age between 75 to 200 Extremely hard, indigestible seeds are excreted unharmed from years. However, longer an animal that may eat them. palmetto stems were not uncommon and Dr. Saw Palmetto Plant-Animal Interaction Review Abrahamson judged that some saw palmettos he Leaves as food: example-blue tortoise beetle measured could be well Nectar as food: examples-bees, wasps, flies, butterflies over 700 years old! Palm hearts as food: example-black bear Berries as food: example-raccoons, deer, black bear, gray fox, Scrub palmettos have a wild turkey subterranean, curved Seeds as food: example- palm seed weevil stem so their age cannot Fibers for nesting: example-grasshopper sparrow be estimated using this method. Shelter in leaves: Examples-frogs, lizards, spiders, insects Shelter in thickets: examples-panther, black bear, deer, raccoon, gray fox, opossum, wild turkey, eastern towhee, snakes Habitat maintenance for wildlife: since palmettos burn easily they can help carry fire through the scrub habitat Medicine: example-humans IV.A.1 Palmettos: Old-Timers of the Scrub Concepts: Adaptations, plant-animal interactions, food webs, predator/prey relationships, microhabitats, diversity of life, and mutualism. Skills: Observation, cooperative learning, measurement, scientific method, and discussion. Time needed: Part One: approximately 20 minutes. Part Two: approximately 30 minutes. Best time of year: anytime Sunshine State Standards: LA.A.1.2.1, LA.A.1.2.2, LA.A.1.2.4, LA.A.2.2.1, LA.A.2.2.5, LA.A.2.2.8, LA.B.1.2.3, LA.B.2.2.1, LA.B.2.2.2, LA.B.2.2.3, LA.B.2.2.6, LA.C.1.2.1, LA.C.1.2.3, LA.C.1.2.4, LA.C.1.2.5, LA.C.3.2.2, LA.C.3.2.5, MA.A.1.2.3, MA.A.3.2.3, SC.F.1.2.2, SC.G.1.2.1, SC.G.1.2.2, SC.G.1.2.5, SC.G.1.2.6, SC.G.2.2.1, SC.G.2.2.2, SC.H.1.2.1, SC.H.1.2.2, SC.H.1.2.3, SC.H.1.2.4, SC.H.3.2.2, SC.H.3.2.4. During Part One of this activity, your class will observe palmettos and animals found on the fronds and stem. Your students will also measure the length of the palmetto stem to help calculate the approximate age of the plant. During Part Two, your class will use data collected to construct a palmetto time line. IV.A.1 Part One—Collecting Palmetto Data Materials needed: Each team of 2-3 students needs: Data sheet Clipboard Pencil String (not too thin) approximately 5 meters long Scissors (or teacher can have) Meter sticks or metric rulers Teacher needs: Extra pencils or pencil sharpener Flagging to mark palmettos and boundaries (optional) Whistle (optional) Calculator Garden clippers (optional) Instructions for the teacher: 1. Locate an area with enough saw palmettos for each team of 2-3 students to have a plant to investigate. Use flagging to mark palmettos or the boundaries, if necessary. 2. Use the information from the introduction to initiate a palmetto discussion with your class. Talk with students about the two different types of palmettos and how important they are for animals and humans. (Humans have used palmetto fronds, including those from cabbage palms, to thatch roofs, make hats, and to spread on sandy roads to prevent cars from getting stuck. Other parts of the palmetto plant have been used as food and medicine.) 3. Distribute and review student data sheet: Palmettos: Old-Timers of the Scrub. 4. Remind your students to observe carefully. Many insects and small animals (tree frogs, lizards, spiders) can be seen on palmettos if the student approaches the plant very slowly and quietly and observes the palmetto before touching the fronds. Wasps will sometimes build nests on palmetto fronds, too, so it is important that they look before charging in. 5. Divide the class into teams. One student should be the recorder. Take the class outside to look for palmettos. 6. Instruct students to observe their palmetto and begin answering questions on their data sheets. Spend at least 5-6 minutes looking over the palmetto carefully. Examine the leaf petiole, palmetto stem (trunk), and palm boots that line the stem. Students may want to cut away some of the dead leaves or leaves that prevent them from getting a clear view of the palmetto stem. If the students see an animal, they should try to watch it without disturbing it and try to decide what the animal is doing. Remember, knowing the correct name of the organism (plant or animal) is not important. Instead, students should give the animal a descriptive name like yellow and black spider, green lizard, or green velvety moss. 7. When observations are completed, instruct the teams to carefully stretch their piece of string along the palmetto stem from the front growing tip to the very base of the stem. (The growing tip is the point from which the live leaves are growing--not the tip of the leaf.) If the creeping stem is buried under leaf litter, you might want to excavate some of the litter or dirt from around the stem to see where it goes. Instruct students to cut the string at the spot where it touches the base of the palmetto stem. 1. 8. Instruct students to measure the length of the string and record this information on their data sheets. (This part can be done inside the classroom to keep you from having to take meter sticks out or if you need teams to share meter sticks.) 2. 9. When you return to the classroom, find the age of each palmetto by dividing the length by 1.2. Students should record the age of their palmettos on their data sheets. 10. Create a table on the chalkboard or overhead projector using the example below as a guide. Compile student data on the table. Saw Palmetto Data Team Age of Blooming? Fruit? Plants living on stem Evidence of Animals # palmetto 11. Have a wrap up discussion with your class. Do animals prefer older or younger palmettos? Do older or younger palmettos have more plants growing on them? Why do you think so? Does the stem show evidence of fire? Did you see roots growing out of the stem? Where on the stem? Did you see any evidence of animals feeding on the fruits or leaves? Palm weevil IV.A.1 Part Two—Constructing a Palmetto Time Line This activity will be easier for your students if they have an example of a completed Palmetto Time Line to look at. Materials needed: Each team of students needs: Completed student data sheet from Part One—Collecting Palmetto Data Palmetto Time Line Worksheet History book, encyclopedias, or almanacs Pieces of posterboard (approximately 5” x 28”) that can be taped together as needed (one posterboard (22”x28”) can be divided into 4 pieces lengthwise). Each team may need up to 6 pieces. (Adding machine tape or rolls of paper used for bulletin board backgrounds also works well.) Tape Marker Teacher needs: Calculator Instructions for the teacher: 1. Brainstorm with your class and make a list of important historical dates. These dates can include locally significant ones as well as those relating to Florida and American history and world events. Some examples are listed below: 1497-1512 Florida first explored by Spanish 1763 Florida changed from Spanish rule to English rule. 1821 Florida becomes part of the U.S. 1845 Florida becomes a state 1861 Civil War begins 1917 U.S. enters World War I 1941 U.S. enters World War II 1950 First rocket launched from Cape Canaveral 1966 Kennedy Space Center opened 1971 Disney World opened You might also include the year your school was built or when your town was established. Encourage students to also consider important dates in their own lives such as when they were born, when they moved to Florida, when a brother or sister was born, when they learned to ride a bike, etc. 2. Have students get together with their teams. Each team will need their data sheet, a Palmetto Time Line Worksheet, a piece of posterboard or adding machine tape, some adhesive tape, and a marker. 3. Teams should complete Part One of the Palmetto Time Line Worksheet. 4. Guide your students through the following steps: a. Stretch your string out as straight as you can from the top to the bottom of a piece of posterboard and tape it down. You may need to tape several pieces of posterboard together if you have a very long string. b. Make a mark on the posterboard beside the top of your string. Beside the mark, write the current year. The top of your string represents the growing tip of the palmetto. c. The other end of the string represents the year the palmetto started to grow. Make a mark on the posterboard beside the end of the string. Beside the mark, write the year the palmetto started to grow. (Refer to Part One of your Timeline Worksheet.) d. Next, figure out where the ten events listed on your Timeline Worksheet belong on your string. This requires several steps: First, subtract the year the event happened from the current year. For example, the Declaration of Independence was signed in 1776. When you subtract 1776 from 2000, the answer is 224 years. Now multiply the answer (224) by 1.2 and round off the number. (We multiply by 1.2 because, on average, palmettos grow 1.2 cm. per year.) 224 years x 1.2 cm = 268.8 or 269 cm. Other examples: 1971-Disney World opened. 2000-1971 = 29 years 29 x 1.2 = 34.8 rounded off to 35 cm. 1845-Florda becomes a state. 2000-1845 = 155 years 155 x 1.2 = 186 cm. e. From the top of your string, measure down the same number of cm. as your answer above (269 cm.) and make a mark. Beside the mark, write the year (1776) and the event that happened that year (The signing of the Declaration of Independence). f. Repeat this process for every event listed on your Timeline Worksheet. 1. Find a spot in the classroom where the time lines can be displayed. Have fun! Results After completing this activity, students should: Be able to give examples of plant-animal interactions. Be able to give examples of plant adaptations. Understand the concept of mutualism and give an example. Be able to observe carefully. Further Questions and Activities for Motivated Students When palmettos bloom, many insects visit the flowers in search of nectar and pollen. Watch a flower stalk for 15 minutes. How many insects come to the flowers? How many different kinds of insects can you see? Check the same palmetto flowers at different times of the day. When do you see the most insect activity around the flower? When do you see the least? IV.A.1 Palmettos, Old-Timers of the Scrub Student Data Sheet #1 Team members:_________________________________________________ PART ONE Stand and observe your chosen saw palmetto from a distance of about 60 cm (or about 2 feet): How does it protect itself from heat and sun? How does it protect itself from predators? Is your palmetto growing in a clump with other palmettos? yes no Are there any plants growing on the palmetto? yes no If yes, describe or draw them: Is the palmetto blooming? yes no Does it have fruit? yes no PART TWO Look closely at the palmetto leaves: Are palmetto leaves bigger than the leaves of nearby plants? yes no What does a palmetto leaf feel like? Draw a picture to show the shape of a palmetto leaf: Do you see any insects or other animals sitting on the leaves? Animal What is it doing? (Hiding, hunting, eating, sleeping) example: green lizard hiding PART THREE Look closely at the stem of the palmetto and the ground around it: Carefully stretch a string along the stem. Cut the string so it is the length of the stem. Measure the string to discover the length of the stem (trunk). The stem is _____cm long. Are there any holes or burrows under the stem (trunk)? How many? ____ yes no PART FOUR (inside the classroom) With your teacher’s help, find the age of your palmetto by dividing the length of your palmetto stem by 1.2. Our palmetto is ____ years old. string---- ----growing tip IV.A.1 Palmetto Time Line Worksheet Team members_________________________________________________ How old is the palmetto your team observed? _________ To find out when your palmetto started growing, solve the problem below: _____(fill in the current year) - _____(fill in the age of your palmetto) ________ _____ The year your palmetto started growing PART ONE Using dates from the class brainstorming session, history books, World Almanac, encyclopedias, the Internet, and dates from your own life, list 10 important historical dates that occurred after your palmetto started growing. (Be sure to write down the event and the year it happened.) Example: 1845 Florida becomes a state 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. PART TWO a. Stretch your string out as straight as you can from the top to the bottom of a piece of posterboard and tape it down. You may need to tape several pieces of posterboard together if you have a very long string. b. Make a mark on the posterboard beside the top of your string. Beside the mark, write the current year. The top of your string represents the growing tip of the palmetto. c. The other end of the string represents the year the palmetto started to grow. Make a mark on the posterboard beside the end of the string. Beside the mark, write the year the palmetto started to grow. (Refer to Part One of your Timeline Worksheet.) d. Next, figure out where the ten events listed on your Timeline Worksheet belong on your string. This requires several steps: First, subtract the year the event happened from the current year. For example, the Declaration of Independence was signed in 1776. When you subtract 1776 from 2000, the answer is 224 years. Now multiply the answer (224) by 1.2 and round off the number. (We multiply by 1.2 because, on average, palmettos grow 1.2 cm. per year.) 224 years x 1.2 cm = 268.8 or 269 cm. Other examples: 1971-Disney World opened. 2000-1971 = 29 years 29 x 1.2 = 34.8 rounded off to 35 cm. 1845-Florda becomes a state. 2000-1845 = 155 years 155 x 1.2 = 186 cm. e. From the top of your string, measure down the same number of centimeters as your answer (example: 269 cm.) and make a mark. Beside the mark, write the year (1776) and the event that happened that year (The signing of the Declaration of Independence ). f. Repeat this process for every event listed on your Timeline Worksheet. B. OAK TREES: THE SERVE YOURSELF BUFFET Introduction A few generations ago a large percentage of children grew up on farms. From an early age these children were responsible for tending gardens. They observed and, unconsciously, began to understand the complexity of the biological systems. These children would have fought specific pests on a variety of different plants. Tomatoes had hornworms, potatoes had several kinds of leaf beetles, squash vines had borers, apples had fruit maggots and fruitworms, and so on. These children not only understood that different plants had their own enemies, but they would have known that different parts of a plant may be eaten by particular insects. They would have known to look for Sand live oak cabbage worms on the underside of the leaf, and that cutworms hide in the soil during the day and emerge at night to fell and consume bean plants under cover of darkness. They would have known that some insects attack young plants, other insects attack older plants. They would have understood that a plant does not need to be pest-free in order to thrive and produce a crop. Old farm circulars and rural school leaflets from 50 or 70 years ago included sections on beneficial insects called, “the farmer’s friends.” Children would also have been familiar with these “friends.” When children got bored with pulling weeds and squashing caterpillars all day, their sharp eyes and curious minds were quick to appreciate the dramas of predation. A wasp pounces on a furiously writhing caterpillar, a lady beetle cuts a swath through a patch of aphids, a team of ants find a grasshopper changing its skin, and attack it in its weakened condition. A spider wraps a big June beetle in silk, an assassin bug on a flower subdues a bee, a praying mantis carefully eats the head of a fly that is still buzzing. As crops matured, insects visited the flowers, one kind of bee for the squash, another for the alfalfa. Bumblebees pollinated blueberries; honey bees and solitary bees visited apples and plums. When work was finished in the garden, children possibly postponed the next round of chores by exploring adjacent pastures where dung beetles rolled their trophies home from the cow pat. Or they made little discovery trips to the woods, where Turkey oak caterpillars dropped from the beech trees on invisible silken threads when chased from their rolled leaves by quick-probing warblers. Life of the average child today is much different. They are expected to know and understand very little about the complexity of ecological systems. Does this lack of understanding matter? Yes! Most of the photosynthesis that provides food energy for humans and other animals still takes place in very complex systems. The forests that give us wood and paper need thousands of species in order to function properly. The decontamination of water in lakes and rivers requires a whole web of interacting organisms. Humans have the ability to disastrously simplify these systems so that they no longer work well. Talking about the nitrogen cycle or the hydrologic cycle as if they were mere chemical and physical processes is not enough! If we want our students to become a generation of responsible citizens, we need to introduce them to the complexity of Chapman ecological systems. The oak tree project will, for many students, Oak be their first direct observation of the complexity of familiar ecological systems. This one project cannot completely change the way students view the world. However, it can be an important step toward a more mature and realistic view of the planet they will inherit. Or, to look at it another way, this section may help students enjoy natural diversity and drama in a way that all children might have just a few hundred years ago. Background Information During this activity, students will approach ecological complexity by investigating how plant-eating insects divide up the resources provided by oak trees. A big plant, such as a tree, offers as many different places to live as a good-sized city does to a human, and the choice of different kinds of restaurants is equally large. A single tree has leaves, flowers, buds, twigs, bark, and roots. A single leaf may be old or newly developed, it may be exposed to the sun, or it may be shaded. These distinctions are important to insects. The leaf itself has veins that can be tapped for sap, it has several layers of tissue that can be eaten, and it can even be induced to grow special structures called galls (see page 137). The insects that feed on trees are fussy about where and how they feed. They are picky because these insects are specialized to feed in particular ways. They have no choice in what they do: their mouthparts and digestive systems are adapted for a particular way of eating and processing some special part of the tree. Part of the specialization seen in tree-eating insects is the result of plant defenses. Myrtle Plants do not tamely submit to being gobbled up by insects. oak Different parts of a tree have different kinds of tough, inedible protective coverings. Tender tissues, such as young leaves, may have a protective coat of barbed or hook-shaped hairs. Most tissues have chemical defenses, usually several kinds. In movies, a special agent who is trying to retrieve a stolen document or invention is equipped with all kinds of fancy gadgets to bypass the elaborate security measures of the enemy stronghold and storage vault. Insects that feed on plants are like those secret agents with their fancy gadgets. Like real secret agents, insects are not always successful in penetrating the defenses and gaining the prize. A question often comes up as students begin to explore the diversity of insects that may feed on a single species of tree. “With all these bugs, why does the tree still have leaves on it?” This topic is considered at the end of the project, when the students list the habits of the animals they see on the tree, including predators. The plant-eating insects all have many predators. The predators, the “farmer’s friends” of the old days, keep the tree-eating species under control. A question that almost never comes up, but which is still interesting is, “What is the value of the plant-eating insects?” The value of these insects is that they are, to a large extent, responsible for the diversity that we see in plants as well as the Scrub oak number of interesting and useful features found in each species of plant. Beyond this, the more general value of all biological diversity is that it makes ecological systems more versatile and efficient. Most people, including students, understand and value diversity at some level. For example, we all understand that each person is different, and while life would be simpler if we were all the same, in the long run, humans are very dependent on this diversity. We need people with a variety of different skills and abilities to keep mankind versatile and efficient. (Imagine a town full of dentists!) Extending this principle to the scale of ecological systems is not easy, but it is a step that all biologists and students must eventually take. About Oaks This activity focuses on oaks because the Florida is full of them! The six species that occur in scrub include: scrub oak, sand live oak, myrtle oak, chapman’s oak, runner oak, and the less frequent turkey oak. Except for the turkey oak, all of the oaks are evergreen, which means leaves stay on the trees all year and drop off only as they die. Turkey oaks lose their leaves in winter and tender new leaves emerge in early spring. (Scrub oaks drop almost all their old leaves before new ones emerge, but stay leafless for a very short time.) Most of the leaf eating Some species of oaks occurs in March and April when new growth is easy to eat, or produce acorns with higher after a fire, when the new oak sprouts emerge. tannins than other oaks. When the Florida scrub-jay While many species of plants have flowers with male and caches acorns, it buries female parts to ensure pollination by insects, oak trees have ones heavy in tannins so they are less likely to rot or separate male and female flowers that occur on the same tree. be eaten by animals. Rather than relying on insects for pollination, oak trees need wind to blow pollen from male flowers, or catkins, to petal-less female flowers. Several species of native bees, gall-making wasps, and caterpillars eat pollen produced by male flowers and can be found on the catkins when oak trees bloom in early spring. Oak trees provide essential food for many animals in the scrub. Leaves are eaten by a wide variety of insects, such as grasshoppers, katydids, caterpillars, leafminers, gall-making wasps, and beetles. Tree- and leafhoppers suck sap from twigs and leaves. Acorns, the fruit of the oak tree, are favored More than 50 kinds of gall by weevils and other insect larvae, squirrels, deer, bear, and wasps live on scrub oaks. birds, including the Florida scrub-jay These wasps are so tiny that they couldn’t sting a person, Oaks and acorns contain chemicals called tannins that help even if they wanted to. protect them from being eaten. However, some insects and Different kinds of gall wasps animals have adaptations that help them deal with these usually cause the tree to tannins so they can eat oak leaves anyway! produce different-looking galls. These oak galls are formed by the oak in response to chemicals produced by both the gall wasps as they insert their Many kinds of moth caterpillars, and a few butterfly eggs into leaves, stems, caterpillars, feed on scrub oak leaves. Some caterpillars eat flowers, and fruits, and by entire oak leaves. Others make irregular holes or notches in the larvae that develop the leaves. Others eat the green parts of the leaves and do not inside the gall. The wasp eat the leaf veins, leaving a brown network of veins. Some very larvae feed on the soft and flat moth caterpillars feed inside the leaf, between the upper nutritious flesh of the plant and lower surfaces, and leave behind a brownish or whitish available to them from inside blotch or twisting line. Some kinds of caterpillars use silk to the gall. Larvae remain in the sew together overlapping scrub oak leaves and then feed protective and edible gall within this shelter. until they mature into adults, and then gnaw their way out, leaving tiny neat holes. Leaf miner Leaf roller moth moth Just how the different gall wasps stimulate oaks to form Leaf miners a specific kind of gall is not completely understood. With so many caterpillars eating scrub oak leaves, it is Because galls are often amazing that oaks have any leaves left at the end of summer! complicated structures with However, so many birds and insects feed on caterpillars, their several layers, it appears the numbers are usually kept down to a reasonable level. Florida wasp gives the plant a set of scrub-jays eat lots of caterpillars, and so do digger wasps and instructions (in the form of twig-nesting wasps. Dozens of kinds of little parasitic wasps growth-stimulating and flies prey on caterpillars. When biologists try to raise oak chemicals) that result in the caterpillars to see what kind of moths will develop, frequently special residence and wasps or flies emerge instead. restaurant the wasp larva needs. IV.B.1 OAK TREES: THE SERVE-YOURSELF BUFFET Concepts: Predator/prey relationships, chemical defenses, species diversity, and ecological niches. Skills: Observation, cooperative learning, and data collection. Time needed: Approximately 30 minutes. More time is needed if making a leaf-eating evidence collection (step #8). Best time of year: Spring, when new leaves begin to emerge. Sunshine State Standards: LA.A.1.2.1, LA.A.1.2.2, LA.A.1.2.4, LA.A.2.2.1, LA.A.2.2.5, LA.A.2.2.8, LA.B.1.2.3, LA.B.2.2.1, LA.B.2.2.2, LA.B.2.2.3, LA.B.2.2.6, LA.C.1.2.1, LA.C.1.2.3, LA.C.1.2.4, LA.C.1.2.5, LA.C.3.2.2, LA.C.3.2.5, MA.A.1.2.3, MA.A.3.2.3, SC.F.1.2.2, SC.G.1.2.1, SC.G.1.2.2, SC.G.1.2.5, SC.G.1.2.6, SC.G.2.2.1, SC.G.2.2.2, SC.H.1.2.1, SC.H.1.2.2, SC.H.1.2.3, SC.H.1.2.4, SC.H.3.2.2, SC.H.3.2.4. During this activity, your class will examine oak trees for evidence of the variety of ways insects and small animals consume and use leaves, acorns, and other parts of the tree. IV.B.1 Part One—Collecting the Data Materials needed: Each team of 2 students needs: Data sheet Clipboard Pencils Clippers Small envelope for leaf collection Teacher needs: Flagging to mark boundaries (optional) Instructions for the teacher: 1. Locate an area with enough short scrubby oaks (about the height of your students) so each team of two students can have their own oak tree to explore. This height will allow students to compare exposed leaves from the top of the tree to more protected ones. Identifying the species of scrub oak is not necessary for this activity. Mark the boundaries for your students. 2. Use the question, “Do trees have flowers?” and the information in the introduction to initiate a class discussion about oaks. Be sure your students understand that acorns are the seeds of oak trees. Trees have flowers although they are usually very small and not easily seen. Trees are more likely to be wind pollinated and do not need large, showy flowers. Other plants use large, aromatic, colorful flowers to attract bees and other pollinators. 3. Divide the class into teams of 2 students. (One student will be the recorder and the other will hunt for evidence of leaf eating.) 4. Distribute and review the student data sheets #1 and #2. 5. Take the class outside to explore scrub oaks. 6. Instruct your teams to select a tree to investigate. Have one team member choose a small branch of the tree and begin examining each leaf for evidence that it has been eaten while the other student records information. Students should look for chewed edges, holes, tunnels, or blotches (leaf miners) and for protrusions growing out from the leaf (galls). Encourage your students to look carefully for the small animal that ate part of the leaf. Like many diners who sit in dark corners, many insects prefer to remain inconspicuous and will hide under leaves, in leaf curls, or between leaves that overlap. 7. Students should collect examples of each type of leaf-eating they find and put them in the envelope. Continue until the first student has finished looking at one branch. Students should then switch roles. IV.B.1 Part Two—Making a Collection of Leaf-eating Evidence Materials needed: Leaf-eating evidence from Part One Sheets of 81/2 x 11 posterboard or heavy paper Tape and/or glue Ring binder or rings Instructions for the teacher: 1. Have students tape or glue the leaves to posterboard or heavy paper. 2. Label the collection with the date and location of your study site, and underneath each leaf, identify the “name” of the type of chewing. For a more permanent leaf collection, press the leaves between sheets of newspaper under several books for a week. Then arrange on heavy paper and either cover the pages with clear adhesive paper or laminate them. Put the pages in a binder or hold together with rings. These booklets can be used as references and/or as a comparison for future leaf- eating explorations. Notes Although evidence of leaf-eating can be found any time of the year, the best time for this activity bright is in the spring when the green new growth emerges and the eating insects are present. Check the oaks regularly, beginning in late February. Results After completing this activity, students should: Understand the concept of predator/prey relationships and give examples. Be aware that many plants and animals use chemicals to defend themselves. Understand the concept of ecological niche (which refers to one animal or one population of a species) and how it is different than microhabitat (which refers to a variety of species). Be able to observe carefully and record data. Be able to learn cooperatively Further Questions and Activities for Motivated Students 1. Examine fallen acorns for signs of life. Collect 20 acorns off the ground. How many of those acorns have holes in them? Carefully open the acorns. Do you see any animals in them? If you can see acorns still on the tree, examine them closely to see if they have holes in them, too. 2. In the spring, carefully collect caterpillars from oak leaves and put them in a jar. Give the caterpillar plenty of oak leaves to eat and punch holes in the jar lid so the caterpillars will have fresh air. Draw a picture of each kind of caterpillar you collected. Keep watching your caterpillars to see what kind of moths or butterflies they turn into. Identify and draw a picture of the adults before you release them. 3. During the winter, collect several oak galls without holes in them and put them in a resealable plastic bag. Watch to see what kind of gall-making wasp emerges from the gall. Use a strong magnifying glass to get a good look. IV.B.1 Oak Trees; The Serve Yourself Buffet Student Data Sheet #1 Team members:________________________________________ Use tally marks to help you count the number of leaves in each category. Then record the total. For example: Chewed edge llll 5 llll llll llll ll 2 llll lll 8 15 Type of eating Branch #1 Branch #2 Branch #3 Branch #4 Chewed edge Hole or holes in leaf Leaf mine- tunnels or blotches inside the leaf layers Gall-bumps or fuzzy protrusion on leaf Other evidence- describe Total number of leaves found with evidence of insect eating Location of branch on tree (top, middle, low, inside or outside) IV.B.1 Oak Trees; The Serve Yourself Buffet Student Data Sheet #2 Team members:________________________________________________ Instructions: While you look for chewed leaves, use the table below to record any animals you see in the leaves, on the tree, or in the acorns you pick up. Do you think the animal you found is eating the plant? Or is the animal a predator and hiding so it can catch another animal to eat? Animal found How “L” = leaf eater Where the animal was found? many? “P” = predator Caterpillar llll 5 L Between 2 leaves Caterpillar Beetle Spider Evidence of gall insect Evidence of leaf miner Grasshopper Leafhopper Frog Lizard Weevil Other: Other: GLOSSARY 1. behavioral mimicry- one species of animal acting like another, usually to defend itself. 2. evergreen- having green leaves throughout the year, the leaves of the past season not being shed until new leaves have been completely formed. 3. catkins- a spike of unisexual flowers with no petals. 4. clonal- genetically identical plants that are, in the case of many scrub oaks, connected underground by a common stem. 5. herbivory- the act of plant-eating 6. mutualism- a symbiotic relationship where both partners benefit. 7. petiole- the slender stalk where a leaf attaches to the stem of a plant. 8. population dynamics- changes in population size that result from various forces (such as disease, habitat destruction, predation, etc.) that control and regulate populations over time. 9. predation- an interaction between species in which one species, the predator, eats the other species, the prey. 10. tannins- astringent compounds found in oaks and some other plants. QUESTIONS FOR STUDENT EVALUATION The questions presented below range from easy to difficult. Select questions most appropriate for your students and, if necessary, modify the questions so they will be more useful in your situation. 1. Several kinds of rare plants live in the Florida scrub. In order to preserve them, we need to understand what these plants need. Put a “T” beside the statements below that are true: ___To keep a rare plant from becoming extinct, we need to preserve some of the habitat that the plant lives in. (True) ___We need to know what insects pollinate the flowers of rare plants and know the life cycles of these insects. (True) ___We need to understand the life cycles of rare plants. (True) ___We need to make sure all the rare plants get watered every week. (False) 2. Plants that live in scrub are tough! List 3 adaptations that help plants conserve water. Waxy coating on leaves Tough, thick leaves Leaves held upright to minimize sun exposure during the hottest part of the day Fuzzy leaves Tiny leaves 3. Place a “T” beside the following statements that are true. ___Plants that live in Florida scrub must be able to grow in soil with almost no nutrients. (True) ___Plants that live in Florida scrub have special adaptations to fire. (True) ___Plants cannot protect themselves from insects and animals that eat them. (False) 4. Saw palmetto and scrub palmetto are two plants that are well adapted to Florida scrub and live a long time. Put a “T” beside the following statements that are true: ___Palmettos play an important role in scrub by providing food and shelter for animals. (True) ___Palmettos burn easily and usually die after a fire. (False) ___Saw palmettos can live a very long time and often grow in large thickets. (True) ___Both saw and scrub palmettos produce flowers in the spring. (True) 5. List two ways scrub plants come back after fire. Resprout, reseed (by seeds stored in the sand, from sand pine cones, or dispersed by animals) 6. Palmettos and animals interact in many ways. a. List two animals that eat palmetto berries: Black bears, raccoons, gray foxes, wild turkeys, gopher tortoises b. List two animals that use palmetto thickets or clumps to hide and rest: Florida panthers, deer, raccoons, bobcats, black bear, eastern towhee, insects, frogs, etc. c. List one animal that uses parts of the palmetto when it build its nest: Florida scrub-jays, wild turkeys, grasshopper sparrow 7. Write a food chain that starts with a palmetto as the producer: Possible examples: Palmettos leaves—blue tortoise beetle—Florida scrub-jay—bacteria Palmetto flower nectar—beetle—eastern towhee Palmetto berries—raccoon—Florida panther—bacteria 8. Oak trees are very common in the scrub. Insects and other animals use oak trees as shelter. Circle the letter beside the correct answer: a. Scrub oaks are evergreen and their leaves stay green all year. b. Scrub oaks are wind pollinated. c. Scrub oaks contain a chemical that protects them. d. All of the above. 9. List two animals that eat oak leaves: beetles, caterpillars, leaf miners, leaf hoppers, gall insects 10. Give two examples of how animals use oak trees: Birds use branches and twigs for nests Spiders use branches and leaves to support webs Insects use the trunk and underside of leaves to hide from predators 11. Use the animals below to create a food web, using the oak tree as the producer. oak tree mold gall insect beetle weevils spider bird hawk Many different relationships within the food webs are possible. 12. Why do you think an oak tree produces so many seeds (acorns)? What happens to the acorns? Only a small percentage of acorns actually germinate so an oak tree needs to produce lots and lots of seeds. Many acorns get consumed by Florida mice, Florida scrub-jays, squirrels, deer, weevils, etc. 13. Write a short essay about what you observed while looking for leaves that were eaten by insects. What kind of leaf damage did you find? What kind of insects? What else did you notice?
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