OWL PELLETS, FOOD WEBS, AND PYRAMIDS INTRODUCTION The barred owl inhabits woodlands and swamps in the Eastern part of the United States. This owl is approximately 43-50 cm long with a wingspan of 99-110 cm and has a mass of about 0.8 kg. Owls are nocturnal raptors that feed on small mammals, birds, and reptiles. Owls swallow their food whole or if too big may tear it into chunks. Owls are not able to digest hair, bones, and feathers. The owl digestive system has a specialized section that presses the undigested portions together forming a pellet. Since the owls cannot pass the pellet through their digestive system, they must spit out the pellet. OBJECTIVES In this experiment, you will Dissect and identify the components of an owl pellet. Calculate the biomass Construct a food diagram (pyramid is a misnomer based on the shape of diagram) Estimate over time MATERIALS Owl pellet Dissecting tools Cup/Beaker Water Butcher Paper (or newspaper) Identification key (Carolina) Skeleton diagrams (Carolina) Sorting sheet (Carolina) 183
Carolina Biological Identification Keys and Skeleton Diagrams http://www.carolina.com/category/teacher+resources/classroom+activities/owl+pellet+interactiv e+database.do?s_cid=url_owls PROCEDURE 1. Use gloves, but also wash hands at the end of the procedure. 2. Put pellet in water for about a minute or until you can see it start to loosen. Use dissecting tools and fingers to gently pry apart the pellet. NOTE: The bones you are looking for are small and easily broken. 3. Set aside any bones found on separate sheet of paper. 4. Repeat until you have completely dismantled the pellet. 5. Separate the skull bones using the following criteria a. Shape and size of the skull b. Shape of eye sockets c. Length of the snout compared to the rest of the skull 6. Use the identification keys to identify the owl s prey. Please remember that voles, mice and rats have similar bones, but there is a huge difference in the sizes (see Table 2 for masses). 7. Clean up: Wrap waste material in newspaper and throw it away; Wash, dry and return dissection equipment - forceps, probes PRE LAB 1. Your food chain consists of the following data, calculate the biomass 2. Draw the pyramid of numbers and the Pyramid of Biomass. Organism Quantities Average Mass (g) Biomass (kg) Plant Plankton 1 0.1 Mussel 200 20 Whelk 1000 10 Herring Gull 5,000,000 200 3. Go to : http://science.malmesbury.wilts.sch.uk/leadictinscience/biology_of_the_seashore.swf 4. Locate a pyramid that is not sustainable. Draw and label it below. Give 2 explanations about what might occur as a result. DATA Fill in Table 1. Use the assumption that an owl produces an average of 2.5 pellets per day. Please note that a vole is equivalent to a mouse TABLE 1. Number of Prey eaten by Owl 184
Prey Mouse or Vole Mole Shrew Rat Bird Number Found (N) Number Eaten per Day (D = 2.5 x N) Total Y T = Number Eaten per Year (Y = 365 x D) POST LAB QUESTIONS 1. Create a two-level Numbers Pyramid (from Data Table 1). There will be no producers in this pyramid. a.) The top level of the pyramid is the secondary consumer. This equals 1 because there is only one owl producing the pellet. b.) The bottom level of the pyramid is the primary consumer. This is the total number of prey eaten per year (Y T ) c.) Make sure to show the correct numerical relationship between top and bottom level. d.) Draw the shape that most biology textbooks use to illustrate food pyramids. 2. Draw and fill in Table 2. Note: Number of prey per year (Y) is from Table 1. Table 2. Biomass of Prey and Producers Prey Number of Prey/year (Y) Mass (kg) (M) Mass of Prey (PM = Y x M) Mass (kg) of Producers eaten by Prey (Prod) Mouse 0.020 45.6 Mole 0.055 365 Shrew 0.005 1168 Rat 0.240 12.8 Bird 0.020 127 Total PM T (kg) Total Biomass of Producers BM T (kg) Biomass of Producers (BM = PM x Prod) 185
3. Use your calculations from Table 2 to create a three-level Biomass Pyramid a. The secondary consumer (top-level) is the Barred Owl and its approximate biomass is indicated in the background information. b. The biomass of all primary consumers (middle-level) is the Total Mass of the Prey (PM T ). c. The biomass of all producers (bottom-level) is the Total Biomass of the Producers (BM T ). 4. Does the shape of the pyramid (from question # 8) illustrate the concept of ecological efficiency of 10%? Table 3. Owl prey and their respective diet Prey Diet It eats a wide variety of plant and animal matter depending on what is available, Mouse including insects and other invertebrates, seeds, fruits, flowers, nuts, and other plant products. A mole's diet is mostly insects and other invertebrates, including earthworms, centipedes, Mole millipedes, snails, slugs, grubs, ants, sowbugs, termites, beetles, and crickets Food habit studies have revealed that shrews eat beetles, grasshoppers, butterfly and moth larvae, wasps, crickets, spiders, snails, earthworms, slugs, centipedes, and Shrew millipedes. Shrews also eat small birds, mice, small snakes, and even other shrews when the opportunity presents itself. Seeds, roots, and other vegetable matter are also eaten by some species of shrews. The rat's diet typically includes seeds, nuts, grains, vegetables, fruits, meats and invertebrates. They consume about one-third of their weight in food every 24 hours. Rat Because of their inability to vomit, rats are very hesitant to try new foods that may be poisonous. They will take a small nibble and wait to see if they feel sick and, if so, will avoid that food in the future. Bird insects; terrestrial non-insect arthropods, seeds, grains, and nuts; fruit 5. Use Table 3 to draw a Food Web that is representative of your pellet. Remember all arrows go from food to feeder to show the movement of energy. Draw and label the owl as the top consumer. Draw and label all prey found in the pellet as the next level of consumer (shrew). Draw and label any consumers eaten by the prey (crickets eaten by shrew). Draw and label any producers eaten by prey or any producers eaten by consumers eaten by prey (seeds, fruit and grass eaten by crickets; seeds and roots eaten by shrew). Draw energy arrows from victim towards consumer (head of the arrow points towards consumer) - From each producer towards each primary consumer that eats that producer. Repeat for each level towards the owl. Note: some arrows may be drawn sideways. 6. Why are the arrows pointing toward the top of the food web? 186
Post Lab 1. What happens to the number of producers if there is plenty of sunshine and rain? 2. What therefore happens to the number of consumers if there is plenty of sunshine and rain? 3. What would happen to the number of prey if the owl was removed due to something like habitat destruction? Why? 4. How would this change the shape of the Numbers Pyramid? Why? 5. How would this change the shape of the Biomass Pyramid? Why? 6. Would this cause the collapse of the food web? 7. If the owl population increases over the next 5 years, what would that do to the food web you created from Table 2? Specifically mention organisms found in the food web. 8. If the vole was removed from the web because of a pesticide. How would this affect the rest of the organisms in the web? Be specific and mention trophic levels. 187
TEACHER PAGES 1. There are three types of pyramids that can be drawn: Pyramid of numbers, biomass, and energy. Other Resources Virtual Owl Pellet Dissection: http://www.kidwings.com/owlpellets/flash/v4/index.htm Carolina Biological Identification Keys and Skeleton Diagrams 188
http://www.carolina.com/category/teacher+resources/classroom+activities/owl+pellet+interactiv e+database.do?s_cid=url_owls Procedure 8. Use gloves, but also wash hands at the end of the procedure. 9. Put pellet in water for about a minute or until you can see it start to loosen. Use dissecting tools and fingers to gently pry apart the pellet. NOTE: The bones you are looking for are small and easily broken. 10. Set aside any bones found on separate sheet of paper. 11. Repeat until you have completely dismantled the pellet. 12. Separate the skull bones using the following criteria d. Shape and size of the skull e. Shape of eye sockets f. Length of the snout compared to the rest of the skull 13. Use the identification keys to identify the owl s prey. Please remember that voles, mice and rats have similar bones, but there is a huge difference in the sizes (see Table 2 for masses). 14. Clean up: Wrap waste material in newspaper and throw it away; Wash, dry and return dissection equipment - forceps, probes PRE LAB 5. Your food chain consists of the following data, calculate the biomass 6. Draw the pyramid of numbers and the Pyramid of Biomass. Organism Quantities Average Mass (g) Biomass (kg) Plant Plankton 1 0.1 500 Mussel 200 20 20 Whelk 1000 10 2 Herring Gull 5,000,000 200 0.2 7. Go to : http://science.malmesbury.wilts.sch.uk/leadictinscience/biology_of_the_seashore.swf 8. Locate a pyramid that is not sustainable. Draw and label it below. Give 2 explanations about what might occur as a result. 189
There is not enough to eat so the population may eventually die out and animals could go extinct. 9. What would occur if the plant plankton was removed from the food web? It would collapse because there would not be enough producers to support the consumers 10. Click on the first food chain circle. Why would this food chain be considered unsustainable? It is unsustainable because there are a lot more primary consumers than producers. Therefore, there are not enough producers to supply energy to the upper levels. DATA Fill in Table 1. Use the assumption that an owl produces an average of 2.5 pellets per day. Please note that a vole is equivalent to a mouse TABLE 1. Number of Prey eaten by Owl Prey Number Found (N) Number Eaten per Day (D = 2.5 x N) Number Eaten per Year (Y = 365 x D) Mouse or Vole 14 35 12,775 Mole 17 42.5 15,512.5 Shrew 7 17.5 6,387.5 Rat 0 0 0 Bird 0 0 0 Total Y T = 34,675 POST LAB QUESTIONS 1. Create a two-level Numbers Pyramid (from Data Table 1). 190
There will be no producers in this pyramid. a.) The top level of the pyramid is the secondary consumer. This equals 1 because there is only one owl producing the pellet. b.) The bottom level of the pyramid is the primary consumer. This is the total number of prey eaten per year (Y T ) c.) Make sure to show the correct numerical relationship between top and bottom level. d.) Draw the shape that most biology textbooks use to illustrate food pyramids. 2. Draw and fill in Table 2. Note: Number of prey per year (Y) is from Table 1. 191
Table 2. Biomass of Prey and Producers Prey Number of Prey/year (Y) Mass (kg) (M) Mass of Prey (PM = Y x M) Mass (kg) of Producers eaten by Prey (Prod) Biomass of Producers (BM = PM x Prod) Mouse 12,775 0.020 255.5 45.6 11650.8 Mole 15,51.5 0.055 853.2 365 311418 Shrew 6,387.5 0.005 31.9 1168 37259.2 Rat 0 0.240 0 12.8 0 Bird 0 0.020 0 127 0 Total PM T (kg) 1140.6 Total Biomass of Producers BM T (kg) 360,328 3. Use your calculations from Table 2 to create a three-level Biomass Pyramid a. The secondary consumer (top-level) is the Barred Owl and its approximate biomass is indicated in the background information. b. c. The biomass of all primary consumers (middle-level) is the Total Mass of the Prey (PM T ). d. The biomass of all producers (bottom-level) is the Total Biomass of the Producers (BM T ). 4. Does the shape of the pyramid (from question # 8) illustrate the concept of ecological efficiency of 10%? No, it is less efficient than 10% Table 3. Owl prey and their respective diet 192
Prey Diet It eats a wide variety of plant and animal matter depending on what is available, Mouse including insects and other invertebrates, seeds, fruits, flowers, nuts, and other plant products. A mole's diet is mostly insects and other invertebrates, including earthworms, centipedes, Mole millipedes, snails, slugs, grubs, ants, sowbugs, termites, beetles, and crickets Food habit studies have revealed that shrews eat beetles, grasshoppers, butterfly and moth larvae, wasps, crickets, spiders, snails, earthworms, slugs, centipedes, and Shrew millipedes. Shrews also eat small birds, mice, small snakes, and even other shrews when the opportunity presents itself. Seeds, roots, and other vegetable matter are also eaten by some species of shrews. The rat's diet typically includes seeds, nuts, grains, vegetables, fruits, meats and invertebrates. They consume about one-third of their weight in food every 24 hours. Rat Because of their inability to vomit, rats are very hesitant to try new foods that may be poisonous. They will take a small nibble and wait to see if they feel sick and, if so, will avoid that food in the future. Bird insects; terrestrial non-insect arthropods, seeds, grains, and nuts; fruit 5. Use Table 3 to draw a Food Web that is representative of your pellet. Remember all arrows go from food to feeder to show the movement of energy. Draw and label the owl as the top consumer. Draw and label all prey found in the pellet as the next level of consumer (shrew). Draw and label any consumers eaten by the prey (crickets eaten by shrew). Draw and label any producers eaten by prey or any producers eaten by consumers eaten by prey (seeds, fruit and grass eaten by crickets; seeds and roots eaten by shrew). Draw energy arrows from victim towards consumer (head of the arrow points towards consumer) - From each producer towards each primary consumer that eats that producer. Repeat for each level towards the owl. Note: some arrows may be drawn sideways. 193
6. Why are the arrows pointing toward the top of the food web? The consumers are eating the food level below them therefore they are getting the energy. Post Lab 1. What happens to the number of producers if there is plenty of sunshine and rain? The amount and biomass of producers increases. 2. What therefore happens to the number of consumers if there is plenty of sunshine and rain? Therefore, the amount and biomass of consumers increases. 3. What would happen to the number of prey if the owl was removed due to something like habitat destruction? Why? The prey would increase exponentially. If they had no natural predators to control the population, then it would grow rapidly. 4. How would this change the shape of the Numbers Pyramid? Why? The secondary consumer level would be nonexistent and the primary consumer level would be much thicker. If there are no secondary consumers to eat the primary consumers, then their numbers will increase. 5. How would this change the shape of the Biomass Pyramid? Why? The secondary consumer level would be nonexistent, the primary consumer level would be much 194
thicker, and the producer level would decrease considerably. If the primary consumer levels increase, then there will be more consumers that eat the producers, causing the biomass of the producers to decrease. 6. Would this cause the collapse of the food web? Yes, it would. There may not be enough producers to support the consumption rate of the primary consumers. 7. If the owl population increases over the next 5 years, what would that do to the food web you created from Table 2? Specifically mention organisms found in the food web. The food web would collapse. The owls would over eat and the bird, mouse, shrew, rat, and vole and their population would decrease. Therefore, the plant biomass would thrive in over abundance. 8. If the vole was removed from the web because of a pesticide. How would this affect the rest of the organisms in the web? Be specific and mention trophic levels. The owl population would decrease because of lack of food. Therefore, the other primary producers would thrive and the producers would decrease do to overeating. 195
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AP* Environmental Science: Name: Period: Directions: Answer the question; the suggested time is about 22 minutes for answering this question. Write all your answers on the lines following the question and not on a separate piece of paper. Where calculations are required, clearly show how you arrived at your answer. Where explanation or discussion is required, support your answers with relevant information and/or specific examples. Species such as the dusky seaside sparrow, the passenger pigeon, and the woolly mammoth are extinct. Populations of other species have declined to the point where they are designated as threatened or endangered. (a) Identify one threatened or endangered species and explain why its population has declined. (b) Describe three characteristics of organisms that would make them particularly vulnerable to extinction. (c) Present three arguments in favor of the maintenance of biodiversity. (d) Name and describe one United States federal law or one international treaty that is intended to prevent the extinction of species. (1) Test Questions are Copyright 1984-2002 by College Entrance Examination Board, Princeton, NJ. All rights reserved. For face-to-face teaching purposes, classroom teachers are permitted to reproduce the questions. Web or Mass distribution prohibited. (2) AP is a registered trademark of the College Entrance Examination Board. The College Entrance Examination Board was not involved in the production of and does not endorse this product. Permission is granted for individual classroom teachers to reproduce the activity sheets and illustrations for their own classroom use. Any other type of reproduction of these materials is strictly prohibited. 201
AP* Environmental Science Name: Period: 202
AP* Environmental Science Name: Period: 203
2000 AP ENVIRONMENTAL SCIENCE FREE-RESPONSE QUESTIONS 3. Species such as the dusky seaside sparrow, the passenger pigeon, and the woolly mammoth are extinct. Populations of other species have declined to the point where they are designated as threatened or endangered. (a) Identify one threatened or endangered species and explain why its population has declined. (b) Describe three characteristics of organisms that would make them particularly vulnerable to extinction. (c) Present three arguments in favor of the maintenance of biodiversity. (d) Name and describe one United States federal law or one international treaty that is intended to prevent the extinction of species. Copyright 2000 College Entrance Examination Board and Educational Testing Service. All rights reserved. AP is a registered trademark of the College Entrance Examination Board. -4- GO ON TO THE NEXT PAGE. 204
AP Environmental Science 2000 Scoring Standards Question 3 Scoring Guide (a) 2 POINTS MAXIMUM 1 point earned for identification of a specific species. General names are not accepted (e.g., whale, owl), unless all members of the group are endangered (e.g., elephant). Examples of Species Accepted Giant panda, elephant, whooping crane, manatee, rhinoceros, California condor, bald eagle, western lily, wooly spider monkey, Florida panther, blue whale, Galapagos tortoise 1 point earned for explanation linked to species above Examples of Explanations Accepted habitat alteration for a specific reason, such as: - human encroachment (urban sprawl) - fragmentation (building highways) - conversion (building a marina) - simplification (agriculture) OR - identification of the specific habitat altered (e.g., The bamboo forest needed by the giant panda has been destroyed. ) hunting or poaching for a specific reason (e.g., food, sport, commercial, cultural beliefs) inability to compete with non-native or invasive species (must be specific, e.g., Arrowroot is outcompeted by the non-native purple loosestrife. ) pollution (must be specific, e.g., Lead poisoning of bottom-feeding waterfowl. pest control (must be specific, e.g., DDT causes thin egg shells in bald eagles. ) (b) 3 POINTS MAXIMUM Each characteristic must be clearly described, explained, or a specific example must be provided (only first three are graded) Acceptable characteristics (need description) - specialized feeding behavior/food source - requires large territory - preys on livestock/people - competition with humans (for space/food) - no natural defense (against introduced species) - fixed migratory patterns - specialized reproductive behavior, breeding - low reproductive rate - limited geographic range, habitat - specific behavior patterns - exploited for economic value (specific) - k-strategist - feed at high trophic level, biomagnification - large size - slow speed - limited range of tolerance - small population linked to lack of genetic diversity Copyright 2000 College Entrance Examination Board and Educational Testing Service. All rights reserved. AP is a registered trademark of the College Entrance Examination Board. 205
AP Environmental Science 2000 Scoring Standards (c) 3 POINTS MAXIMUM 1 point earned for each argument (only first three are graded) ecosystem function and/or stability based on a specific reason such as - organism's role in food web (e.g., keystone species, predator-prey relationships) - organism's role as a pollinator - organism's role in nutrient cycles (e.g., decomposer, nitrogen-fixer) future medical resources future food resources economic potential (ecotourism, future products with market value) genetic bank (species diversity to allow continued evolution) recreation (hiking, camping, hunting, fishing, etc.) scientific value for research/natural lab scenic/aesthetic value symbolic/religious value intrinsic value/ethical reasons (organism have inherent right to live, ecological wealth) provides resources for indigenous human population minimizes spread of infectious diseases (d) 2 POINTS MAXIMUM 1 point earned for naming the law or treaty 1 point earned for describing the law Federal Laws (1 point) Components (1 point; need ONE of the following) Endangered Species Act - identify species that are endangered/threatened or (ESA) - protect endangered species from one of the following: import/export, taking, harassing, harming, hunting, shooting, wounding, trapping, killing, capturing, collecting, possessing, selling, delivering, transporting, shipping, receiving or - penalize violators or - design protection plans or - reintroduce species or - protect habitat Lacey Act - prohibits transport of protected species between states The following are also acceptable with a correct description: Wild Bird Conservation Act Eagle Protection Act Migratory Bird Treaty Act African Elephant Conservation Act Whaling Conservation and Protection Study/Act Fur Seal Act Marine Mammal Protection Act Whaling Convention Act Migratory Bird Conservation Act Fish and Wildlife Conservation Act Fish and Wildlife Coordination Act Fish and Game Sanctuary Act Marine Protection, Research and Sanctuary Act Fish and Wildlife Act Wildlife Restoration Act of 1937 (Pittman-Robertson Act) National Wildlife Refuge System Administration Act International Treaties: CITES (Convention on International Trade in Endangered Species) regulates international trade of protected species and their products Convention on Biological Diversity treaty signatories are expected to adopt biodiversity plans, establish protected ecosystems, promote sustainable use of biological resources, restore degraded habitats, protect threatened species International Whaling Commission Ban on Whaling imposed moratorium on whaling Copyright 2000 College Entrance Examination Board and Educational Testing Service. All rights reserved. AP is a registered trademark of the College Entrance Examination Board. 206
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AP ENVIRONMENTAL SCIENCE 2000 SCORING COMMENTARY Question 3 Sample Q Score 10 This student gave a thorough answer that was typical of students who scored highly on the question. An endangered species (giant panda) was identified and a reason for its declining population given. Three characteristics that would make a species vulnerable to extinction were cited and clearly explained. The student presented three sound arguments for maintaining biodiversity, before going on to name and describe the Endangered Species Act. Sample R Score 8 This student did not correctly identify an endangered species, but scored the maximum number of points in the other sections. Well-explained examples were given in part (b), and concise arguments made in part (c). The Endangered Species Act was named and described in part (d). Sample S Score 6 The manatee was named as the endangered species and a reason for its decline stated. The student scored full points in part (b), did not any receive credit for part (c), and was awarded one point for naming the Endangered Species Act. Question 4 Sample Q Score 10 The student gave a well thought out answer, representative of those receiving a high score on this question. The countries with the largest and smallest rates of population growth were correctly identified and explained. A sound comparison and reasoning for the difference in infant mortality between Countries X and Y was given in part (b). The description of the demographic transition was concise and showed a high degree of clarity, scoring maximum points for part (c). In part (d), an incentive was stated and a linked drawback to the incentive was described, allowing the student to receive one point for each. Sample R Score 8 The student received the maximum number of points in parts (a) and (b), but only attained one point in part (c) for stating that both the birth and death rates decrease as a country becomes industrialized. One point was given for naming an incentive and a further point was attained for a linked drawback in part (d). Sample S Score 6 This paper is a good example of a student answer that scored in the mid-range for this question. The student correctly identified Country X as having the largest and Country Y as having the smallest rate of population growth, receiving one point for each answer. No credit was given for part (b). One point was awarded in part (c) for stating that both the birth and death rates decrease as a country becomes industrialized. In part (d), the student scored the maximum number of points for naming an incentive, explaining how it would work, and describing a drawback which was linked to the incentive. Copyright 2001 by College Entrance Examination Board. All rights reserved. Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board. 3 210