LAB 5: Predator-Prey and Population Growth -- INSTRUCTIONS In lab this week you will investigate quantitative models of population growth and consider the impact of barn owls on their prey population by observing the dissection of pellets containing food remnants and using those remnants to quantify food consumption. To prepare for lab please read about bird populations (p. 140-143) and predatory birds such as owls (p. 114117 and 225) in your textbook and this entire unit. Bring your FIELD GUIDE and calculator. Supplies (for in-person lab) Dice (5 per group) Owl pellets Dissecting pans Dissecting microscopes Forceps, toothpicks, wooden sticks Clear tape Laminated bone charts and skeleton figures Rat skeleton Part I: Owl pellets Without teeth to grind up their food, birds swallow prey whole or in large chunks. To eliminate the non-digestible portions of prey, such as bone and fur, owls regurgitate a pellet containing this waste from their stomach every day before hunting the next night. Owl pellets have been collected at sites where barn owls live and sterilized for classroom use. Watch the demo video of an owl pellet dissection, then tally up the bones from three different owl pellets in the photographs provided on CANVAS. To help you identify the bones, there several resources available in the Bone Guide. Most prey are rodents so we categorize them according to size: voles are smallest, then mice, then rats, then squirrels. Record the numbers of the main types of bones on the Worksheet (question 1) and answer questions 2-3. Next, you will answer questions, do calculations, and make a graph using data from a larger set of owl pellets. Combine the three you tallied above with another eight reported by students in 2018 and 2019. Specifically, former students found the following prey items in Pellet #4: 1 mouse, 1 bird Pellet #5: 1 vole Pellet #6: 1 vole, 3 mice Pellet #7: 1 mouse, 1 squirrel Pellet #8: 1 shrew, 1 rat Pellet #9: 3 voles, 2 mice Pellet #10: 1 vole, 1 bird Pellet #11: 2 voles, 2 mice Answer questions 4-7 on the Worksheet. Part II: Population Growth Humans rely upon many natural products for food, clothing, and shelter. Many of the resources used, such as plants and animals, are considered to be renewable, because the populations of utilized organisms reproduce and replace the individuals removed by people. Unfortunately, our rapid population growth in the last hundred years has put 1 tremendous strain on many natural resources. Large areas of land that were previously forested are now bare and once abundant game animals are now scarce. In order to properly manage our resources it is necessary to have a full understanding of the population biology for a particular species. Often only incomplete information is available and so biologists have to make educated guesses about how much of the resource population can be safely harvested. Models and simulations provide useful tools for exploring how different conditions affect population growth. Today you will carry out a simulation to see how commercial fishing affects fish populations. 1. Logistic growth model Many populations of organisms exhibit what is called logistic growth if space and food are limited. The equation that describes this type of growth is I = r N [(K – N)/K] where I = rate of increase in the population over time r = intrinsic rate of population growth (related to organism’s life history) N = size of the population K = carrying capacity of the environment A graph of logistic growth for a hypothetical population has a characteristic Sshaped curve (Fig. 1). The slope or steepness of the curve represents the rate of population growth. Note that when the population level (N) is low relative to K, growth is slow because there are few individuals to reproduce. When the population level is close to K, growth is slow because resources are limited. Population growth is most rapid at an intermediate population size. Fig. 1: Logistic growth curve 2. Commerical fishing simulation In this exercise you will simulate fishing at three different quota levels to see how the population is affected. Table 1 prescribes annual fish harvests and Table 2 represents the reproductive capability of a fish population based on the logistic growth equation (see above) 2 with r = 0.8 and K = 50. When the fish population is either low (near 0) or high (near 50), growth is slow, whereas when population size is intermediate (near 25), growth is rapid. Procedure You will start with a population of 50 fish and proceed with 10 cycles of harvesting and reproduction. Five dice will be rolled to determine the catch for each year/generation. Here’s an online 5-dice roller you can use if you don’t have Yahtzee. Table 1 gives the harvesting rules for each quota level and Table 2 tells you how many new fish to add back after each harvest. Each person should run their own simulations. Record the results in three Tables under question 1 on the Worksheet. Table 1. Rules for fish harvest are based on rolling five dice at once. Quota level Number of fish to catch 1 Add face values (1-6) of five dice 2 One fish for every “1” on the dice and two fish for every “2” or higher on the dice 3 One fish for every “5” or “6” on the dice and zero fish for every “4” or lower on the dice Limit per round 30 10 5 Table 2. Population growth based on population size. Logistic growth equation used with r = 0.8 and K = 50. White columns represent reproduction. # fish after # new fish to # fish after # new fish to # fish after # new fish to harvest add prior to harvest add prior to harvest add prior to next harvest next harvest next harvest 1 0 18 9 35 8 2 2 19 9 36 8 3 2 20 10 37 7 4 3 21 10 38 7 5 4 22 10 39 7 6 4 23 10 40 6 7 5 24 10 41 6 8 5 25 10 42 5 9 6 26 10 43 5 10 6 27 10 44 4 11 7 28 10 45 4 12 7 29 10 46 3 13 7 30 10 47 2 14 8 31 9 48 2 15 8 32 9 49 1 16 9 33 9 50 0 17 9 34 9 Answer questions 2-7 on the Worksheet. 3 LAB 5: Predator-Prey and Population Growth -- WORKSHEET Part I: Owl pellets 1. List the numbers of bones of each type found in the owl pellets that are shown in pictures. Pellet #1 Pellet #2 Pellet #3 Skull R or L jaw bone R or L scapula R or L pelvic bone R or L humerus Total radius/ulna R or L femur Total tibia/fibula Total prey 2. Based on the bone counts, how many prey did each owl eat recently? Put your values in the table above and explain which bones helped you decide. 3. Given the shapes and relative sizes of the bones, which prey types are represented in each of the above pellets? 4. Now look at the prey identified across pellets #1-3 above and #4-11 on the Instruction page. List three distinct factors that could account for diet differences among owls. 5. Calculate the average number of total prey animals per pellet, using results from all eleven pellets. Then figure out the average # of prey animals per pellet for each different type of prey we identified. Show your work. 1 6. Make a bar graph to illustrate the results. Every graph requires a descriptive title, clear labels on the y-axis and x-axis, and units for quantitative data. 7. If one pellet represents an owl’s food daily intake, how many prey are consumed in one week? One month? One year? Use the average prey/pellet and show your work. 2 Part II: Population Growth -- Commerical fishing simulation 1. Complete the three Tables below by following the procedure and harvest rules on the Instruction page. Add the summary information at the end of each quota level as well. Quota level 1 (highest harvest levels) Generation Initial population # harvested (roll size (sum of # dice and follow remaining and # Table 1 rules) added) 1 50 2 3 4 5 6 7 8 9 10 Total # of fish harvested in ten rounds _____ Total # of fish surviving after ten rounds _____ Quota level 2 (intermediate harvest levels) Generation Initial population # harvested (roll size (sum of # dice and follow remaining and # Table 1 rules) added) 1 50 2 3 4 5 6 7 8 9 10 Total # of fish harvested in ten rounds _____ Total # of fish surviving after ten rounds _____ 3 # remaining (subtract # to add (look harvest from initial up in Table 2) size) # remaining (subtract # to add (look harvest from initial up in Table 2) size) Quota level 3 (lowest harvest levels) Generation Initial population # harvested (roll size (sum of # dice and follow remaining and # Table 1 rules) added) 1 50 2 3 4 5 6 7 8 9 10 Total # of fish harvested in ten rounds _____ Total # of fish surviving after ten rounds _____ # remaining (subtract # to add (look harvest from initial up in Table 2) size) 2. Within your lab group, calculate the average # fish harvested and the average # fish surviving after 10 rounds at each quota level. Show your work. GROUP DATA Quota level 1 2 3 Average # fish caught Average # fish surviving 3. What is the advantage of using group averages instead of only your own data? 4. Quota level 1 provided the greatest harvest early in the simulation. How did these early yields affect fishing over the long term? 4 5. Where on the population growth curve (bottom, middle or top of Fig. 1) should most fishing industries operate in order to maximize profits and sustain the resource? Explain. 6. Give one specific example of overfishing in the world. 7. How does this simulation relate to avian biology? 5 Bone identification guide (see subsequent slides also) Owl pellet #1 in foil Watch video of dissection from 1:00-7:00 min (on CANVAS) -- process took about 45 min total Owl pellet #1 divided into bones vs. fur Owl pellet #1, bones sorted, close-ups follow Owl pellet #1 – lower right section of plate Owl pellet #1 -- upper right section of plate Owl pellet #1 -- upper left section of plate Owl pellet #1 – lower left section of plate Owl pellet #2 Owl pellet #3 
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