Understand and explain the value of running numerous replicates of an experiment as compared to making inferences based on a small sample size
Download the attached pdf file for this Problem Set. Please note the due date and time complete this by tomorrow afternoon, thank you. Follow the instructions for completing your work and naming the file. Please show work when applicable
Requirements: 5 questions
1 WIS 3404 Natural Resource Ecology—Fall 2023 Dr. Steve A. Johnson—University of Florida Problem Set 2 Optimal Foraging Strategy DUE: Friday, September 29th @ 10pm EST Learning Objectives: • Understand and explain the value of running numerous replicates of an experiment as compared to making inferences based on a small sample size • Create a chart/graph using raw data and labeling the graph correctly • Interpret data presented in a chart/graph in a clear and concise manner • Develop critical thinking skills by explaining the tradeoffs for a predator under an optimal foraging strategy Overview: The Problem Sets you must complete in this course cover topics related to chapters in the text and important issues in ecology and natural resource conservation. Some of the original problem sets were provided by the publisher of your course textbook Ecology by Bowman & Hacker. Your instructor has modified the questions in the original problem sets, so be sure to answer the questions listed below on this assignment sheet, and not the questions at the text website. Most of the Problem Sets (including this one) require you to visit the textbook’s Oxford Insight website in order to conduct computer simulations to complete the assignment. This is the same site you use to access the eBook’s chapters for your reading assignments, so by now you are already familiar with it—it’s at this link. Problem Sets are designed to improve your critical thinking skills by analyzing and interpreting scientific data and answering questions based on the data. Instructions: Answer the questions below based on the results of the computer simulation that you will run at the textbook’s Oxford Insight website. You must submit your answers as a file uploaded into Canvas as described below on this assignment sheet. Do not respond to the questions associated with the simulation. Your responses must be uploaded to Canvas as a MS Word or PDF file by 10:00 p.m. on Friday, September 29th. Late Problems Sets are not accepted—no excuses—do not wait until the last minute to complete and submit Problem Sets. Include the following information in the filename: your last name and first initial, Problem Set number, and name of the assignment (Optimal Foraging in this case). Be sure to follow the file format in this example: LastnameFirstinitial_ProblemSet02_OptimalForage, and do not include any spaces in the filename! Go to the appropriate Problem Set link at Assessments in Canvas and follow the directions for uploading your completed document. Save a copy of the file on your computer as a backup. On the document you submit be sure to include your name, the date, the Problem Set number, and your response to each question in order. You do not need to include the questions, just your numbered responses. And please edit your responses for grammar and
2 spelling. You will lose points for poorly worded responses. Be succinct, but thorough in your responses. This exercise is based on a computer simulation that you must access at the website for the course textbook (5th Edition). The textbook website requires a registration code, which is included with each new textbook/eBook. If you purchase a used book and the code has already been used then you will need to purchase a new code (see the course syllabus for details). Once you have accessed the textbook’s Oxford Insight website, click the link to Chapter 8: Behavioral Ecology and then choose the Hands-On Problem link. Be sure you navigate to Hands-On Problem 8.1 and not the 8.2 option. This will take you to a computer simulation, which may take a few moments to load—you may need to scroll down the page a bit to see the simulation. Use the computer simulation to answer the questions below, NOT the questions listed at the course website. Be sure to follow the directions below under ‘Questions,’ read the questions closely, and answer all parts of each question—answer what is asked. OPTIMAL FORAGING Introduction Organisms often face the choice of whether or not to pursue a prey item. As you will see in Chapter 8 of the textbook, optimal foraging theory predicts that evolution by natural selection will shape organisms such that they forage in an optimal manner, given the constraints of their environment. In the absence of increased risk due to foraging, optimally-foraging organisms will forage so as to maximize net energy gain per unit of time expended. Net energy gain is the energy acquired by metabolizing the food item minus the costs incurred. These costs can arise from many sources, including energy spent searching for the food item, energy spent digesting the food item, as well as energy expended avoiding becoming a food item (e.g., a mouse must avoid predators while searching for food). If the food item is an animal, additional costs may be spent pursuing, fighting, and killing the prey. Some plants have tissues that are difficult to digest or contain secondary compounds that evolved to dissuade herbivores—dealing with such imposes additional energetic costs to predators. As a result, acquiring energy for growth and reproduction is a game of tradeoffs. When prey become scarce due to overharvesting by humans (e.g., sardines harvested for human use), predators may be forced to alter their optimal foraging strategies. This can result in deterioration of the health of the predators and possibly lead to a decline in the predator population. Alternatively, if humans inadvertently “supply” a new prey source (e.g., sheep or calves, garbage) with apparently reduced foraging costs to predators, the predators may begin to target this seemingly less costly prey. Such a situation can result in the predators becoming a nuisance or threat to people, which leads to costly and difficult decisions for natural resource managers.
3 In the simulations that you will complete at the textbook website, you will control a predator (a virtual frog) in search of food, using different foraging strategies and analyzing which strategy provides the highest net energy gain. These simulations consider only costs associated with traveling to the prey and digesting it. Obviously, this is unrealistic in most natural situations, but this simplification makes it easier to build and interpret the simulation. QUESTIONS (Be sure to answer all parts of each question!) Question 1 In the first exercise, you will make the predator go after all prey items regardless of how far they are away or their size (be sure to enter “Max. distance” as 100m and then click reset). Be sure “prey size” is set to small and “number of prey” is set to 10. Click the Start/Stop button (not the Repeat Simulation button) to run the simulation once. Question 1A: How many prey items (there should be 10 prey total) resulted in a net energy gain or loss for the virtual frog predator, and what was the overall net energy gain/loss under this scenario? [Note there is not a specific type of “energy unit” (e.g., calories) associated with the gain or loss. Also, the maximum number of energy gains and or losses is 10, since this the number of prey items set for the simulation.] In this first simulation your sample size was just one (i.e., 1 replicate) since you only evaluated foraging success for one frog. As you may know, making inferences about a sample size of one is not statistically or biologically justifiable. For example, in your single simulation, just by chance most of the prey may have appeared at distances well away from the predator. On the other hand, many of the prey items may have been close to the predator. Either scenario could bias the outcome of your findings leading to erroneous conclusions. To avoid this bias you need to gather data on a much larger sample size. To do this, leave “prey size” and “number of prey” set as before but enter 30 in the “repeat simulation” box and then click the “repeat simulation” button. By doing so, you are replicating your observations 30 times by collecting data for 30 frogs. Thus, your sample size increases from 1 to 30. You will see a box with the average net energy gain/loss and standard error for the 30 runs of the simulation. Question 1B: What was the value for average total net energy for a sample size of 30 frogs and how does this compare to the value of single frog? Question 1C: Does this foraging strategy appear to be optimal for the virtual frog predator? Why or why not? Question 2 Next, follow the rule that the predator will pursue all items that are only 20 m or less away and ignore those that are greater than 20m away. (Remember to reset the maximum foraging distance by entering 20 as the max. distance and clicking reset). Be
4 sure “prey size” is set to small and “number of prey” is set to 10. Click the Start/Stop button to run the simulation once. Question 2A: How many times was there an energy gain or loss for the virtual frog predator, and what was the overall net energy gain/loss under this scenario? Now increase your sample size to 30 frogs. As before, leave “prey size” and “number of prey” set to small and 10 and enter 30 in the “repeat simulation” box and then click the “repeat simulation” button. Question 2B: What was the value for average total energy gain for a sample size of 30 frogs and how does this compare to the value of single frog? Question 2C: Does this foraging strategy appear to be optimal for the virtual frog predator? Why or why not—justify your answer? How did it compare to the strategy of the predators pursing all prey up to 100m away? Question 3 The best way to determine the most optimal foraging strategy for the virtual frog predator would be to collect data on net energy gain/loss for a large sample of frogs at numerous foraging distances. Fortunately, the simulation allows you to do this. Keep the same settings for “prey size” and “number of prey”, but increase the number of replicates to 50 and now run the simulation at intervals of 10m. Begin with the 10m distance and continue out to 100m by increasing the maximum forging distance by 10m at a time. Be sure to record the average total net energy gain or loss for each of the 10 distances (i.e., 10m, 20m, 30m…, 100m). To visualize your results, you need to plot your data on a graph (often referred to as a chart in Excel). Since your data are recorded as average energy gain or loss (i.e., they are single data points, don’t worry about the associated standard errors) across multiple distances, the most appropriate type of graph to create would be a line or scatter plot. (Hint: Microsoft Excel is a quick and easy application to use to create and label your graph.) View these tutorials for tips on how to create and label charts in Excel: • YouTube Excel Video 1 • YouTube Excel Video 2 • Excel Easy Website • Microsoft Excel Support Keep your graph simple and easy to read and interpret. There is no need for fancy colors or 3D styles. Please use black text only on a white background. Be sure to label the X and Y axes and include an overall title that is brief, but descriptive. Once your graph is created in Excel you can simply copy and paste it into a Word file. There are other programs you can use to create this graph, but Excel is probably the easiest to use and most available program. Below is an example of the type of chart you need to submit with your answers. Hand-drawn graphs are not acceptable.
5 Question 3A: What is the most optimal foraging distance for the virtual frog predator under the scenario you used to generate your data, and why? You must provide a detailed explanation that demonstrates critical thinking in your response. Please interpret the data presented in your graph. Remember, you must include a copy of the graph with your answers. Question 4 In the exercises above, all the prey items provided the same amount of energy. Suppose prey items varied in nutritional quality and the amount of energy they provided to the predator. Question 4A: How might this alter a predator’s foraging success and energy gain as well as the predator’s optimal foraging strategy? (Hint: Use the simulation to test your hypotheses regarding prey quality and provide support for your answer.) Question 4B: What additional costs (other than energy expended traveling to prey) are there for real predators and how might these costs influence predator foraging strategy? Question 5 In the Introduction, the statement was made that human-supplied food sources for predators could result in difficult and costly decisions for natural resource managers.
6 Question 5A: Discuss an example or examples of human-supplied food resources for wild animals and how such a situation could cause problems for natural resource managers. What specific problems/issue might managers have to deal with and how could these problems be resolved effectively?
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