Dangerously bold Featured scientist: Melissa Kjelvik from Michigan State University

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1 Dangerously bold Featured scientist: Melissa Kjelvik from Michigan State University Research Background: Just as each person has her or his own personality, animals of the same species can behave very different from one another! For example, pets like dogs have different personalities. Some have a lot of energy, some are cuddly, and some like to be alone. Boldness is a behavior that describes whether or not an individual takes risks. Bold individuals take risks while shy individuals do not. The risks animals take have a big impact on their survival and the habitats they choose to search for food. Bluegill sunfish are a type of fish that lives in freshwater lakes and ponds across the world. Open water and cover are two habitats where young bluegill are found. The open water habitat in the center of the pond is the best place for bluegill to eat a lot of food. However, the open water is risky and has very few plants or other places to hide. Predators can easily find and eat bluegill in the open water. The cover habitat at the edge of the pond has many plants and places to hide from predators, but it has less food that is best for bluegill to grow fast. Both habitats have costs and benefits called a tradeoff. A view of the experimental pond. The center of the pond is the open water habitat with no plants. At the edge of the pond is the cover habitat with plants. At the start of the experiment, 100 bold bluegill, 100 shy bluegill, and 2 largemouth bass predator were placed in the pond. Here, scientists are using a net to collect the surviving bluegill at the end of the experiment. 1

2 Melissa is a scientist who is interested in whether differences in young bluegill behavior changes the habitats they choose to search for food. First, she looked at whether young bluegill have different personalities by bringing them into an aquarium lab and watching their behavior. She saw that, just like in humans and dogs, bluegill sunfish had different personalities. Some bluegill took more risks and were bolder than others. Melissa wanted to know if these differences in behavior changed how the fish behaved back in the pond. She thought that bold fish would take more risks and use the open water habitat more than shy fish. Bold fish would then have more food and grow faster and larger. She thought that shy fish would play it safe and not take risks, so they would use the cover habitat more. Shy fish would then eat less food and not be able to grow as large. Because the bold fish would be in the open water habitat, they might get eaten by predators more because shy fish would avoid predators. These differences in the habitats that the fish use would create a tradeoff based on personality. Melissa designed a study to test the growth and survival of bold and shy fish. When she was watching the fish s behavior in the lab, she determined if a fish was bold or shy. If a fish took the risk of leaving the safety of the vegetation in a tank so that it could eat food while there was a predator behind a mesh screen, it was called bold. If it did not eat, it was called shy. She marked each fish by clipping the right fin if it was bold or the left fin if it was shy. She placed 100 bold and 100 shy bluegill into an experimental pond with two largemouth bass (predators). The shy and bold fish started the experiment at similar lengths and weights. After two months, she drained the pond and found every bluegill that survived. She recorded whether each fish that survived was bold or shy and measured their size (length and weight). Check for Understanding: After reading the Research Background students should be able to describe the tradeoff between open water and cover habitat for young bluegill. describe the two personality types of fish measured in this experiment. make a prediction about how a young bluegill s personality may affect its habitat choice. understand why it was important for Melissa s measure of growth for the bold and shy fish to have a similar size (length and weight) at the beginning of the experiment. give an example of animal personality that they have observed in a species that they are familiar with. Scientific Questions: Is there a tradeoff between being bold or shy? How does the boldness of bluegill affect their survival and growth (length and weight)? What is the hypothesis? Find the hypothesis in the Research Background and underline it. A hypothesis is a proposed explanation for an observation which can then be tested with experimentation or other types of studies. 2

3 To determine their personality, Melissa observed young bluegill sunfish in the aquarium lab. Draw your predictions: Below is a diagram of a pond where you can draw your predictions. Think about how bold and shy fish might respond to a predator. 1. Start by looking at the legend. Do you predict bold or shy fish will grow larger? Label which fish is bold and which is shy and choose a color for each. 2. Now move to the pond diagram. Draw bold and shy fish in the habitats where you predict they will spend most of their time. 3. Draw your survival predictions. Do you predict there will be more bold or shy fish left at the end of the experiment? Add more fish to your diagram if necessary. cover habitat open water habitat = bold predator = shy 3

4 Scientific Data: Finish filling in the table below. Use the data to answer the scientific questions. Bluegill Proportion Percent Average Length Average Weight Behavior Survived Survival Length (mm) SE** Weight (g) SE Bold 66/100 66% Shy 74/100 74% ** Standard error (SE) tells us how confident we are in our estimate of the mean and depends on the number of replicates in an experiment and the amount of variation in the data. A large SE means we are not very confident, while a small SE means we are more confident. Teacher Note: There are several topics you might want to discuss with your students when they are working with these data. Because the dataset is so simple, many students may be able to construct their explanations without making a graph. Encourage your students to make graphs to practice those skills, but when supporting their claim with evidence students can refer back to either the table or graph. See the Meta Moment below. Additionally, this could be a good opportunity to bring up issues of scale with your students. When labeling the y-axis, there is no need to start the scale at zero. Instead, students can start a few numbers below the lowest value (for example, at 62% for the survival data). Scale can also help students interpret whether a small difference between two values is important biologically for the species in the experiment. For example, a weight difference of 0.7 g might seem small, but this is a large difference for tiny fish that only weigh 5 g! Even without statistics, you can have a class discussion on whether the pattern in the dataset follows predictions or does not. You can have students add error bars to their graphs to deepen this discussion or remove standard error (SE) from the table for younger students. Standard deviation (SD) is the most common measure of variation for normally distributed data. It is a measure of the average distance of all values from their mean. The smaller the bars, the less variation around the mean. Standard error is the SD divided by the square root of the study s sample size (SE = SD/ n). Unlike SD, SE reflects uncertainty in our estimate of the mean. The larger our sample size and the less variation in the data, the more confident we can be in our estimate of the mean. Upper error bars are calculated by adding one SE or SD to the mean, and lower bars are calculated by subtracting one SE or SD from the mean. 4

5 Check for Understanding: After taking some time to look at the data table, have students discuss the question, What type of graph should you make? There are many different kinds of graphs, and each is appropriate for different types of data. What type of graph would be most appropriate to make with these data? Bar graphs - suitable for when you have a categorical independent variable and continuous dependent variable. Used to make comparisons among groups. Histograms - suitable for showing the distribution of continuous data. Breaks data into equal intervals. Line graphs - suitable for when you have continuous independent and dependent variables, like changes over time. Used to look at trends. Pie graphs - suitable for showing data that are parts of a whole. What data will you graph to answer the questions? Graph 1: Survival Independent variable: Boldness (shy, bold) Dependent variable: Percent survival Graph 2: Length Independent variable: Boldness (shy, bold) Dependent variable: Average length (mm) Graph 3: Weight Independent variable: Boldness (shy, bold) Dependent variable: Average weight (g) Draw your graphs below: Identify any changes, trends, or differences you see in your graph. Draw arrows pointing out what you see, and write one sentence describing what you see next to each arrow. (1) Many more shy fish survived than did bold fish. (2) Bold fish grew much longer than shy fish. (3) Bold fish grew a little bit heavier than shy fish. 5

6 Percent Survival (1) (2) (3) 70 6 Average Length (mm) Average Weight (g) Bold Shy Fish Boldness 62 Bold Shy Fish Boldness 0 Bold Shy Fish Boldness Interpret the data: Make a claim that answers each of the scientific questions. There is evidence for a tradeoff in growth and survival between the bold and shy bluegill sunfish (there are good and bad consequences about both bold and shy personality types). Bolder fish had lower survival, but showed more growth during the experiment. What evidence was used to write your claims? Reference specific parts of the table or graphs. Bolder bluegill were larger at the end of the experiment (3.0 mm longer and 0.7 g heavier, on average) but showed lower survival (only 66 bold fish survived compared to 74 shy fish). Shy bluegill were smaller at the end of the experiment but had higher survival. Teacher Note: Students will likely come to the conclusion that survival is different for bold and shy bluegill in this dataset. Although shy fish had 74% survival and the bold fish had 66% survival, this difference is not statistically significant. However, you can have a discussion with your students about whether they think an 8% difference is biologically relevant. This experiment was only for 2 months it could be that over a longer time frame, these differences would accumulate. Melissa did one experiment that lasted 9 months, but very few bluegill were eaten by the predators, so the results on survival were inconclusive. 6

7 Explain your reasoning and why the evidence supports your claims. Connect the data back to what you learned about the tradeoff for using the cover and open water habitats. Because shy and bold bluegill started the experiment at similar lengths, we can conclude that bold fish had higher growth rates over the timeframe of the experiment. However, they had lower survival. There is a tradeoff between being bold or shy in young bluegill because there are costs and benefits to each. Survival and growth differed depending on the boldness of the bluegill, just as expected. This probably means that bolder fish were using the risky open water habitat to find food, while the shy fish were using the cover habitat for protection but ate less food. Meta Moment: Have students reflect back on the table and graphs. Poll the class to see how many students referred back to the table, graphs, or both when supporting their claims with evidence. What was the reason for their preference? What makes each easier or harder to use for interpretation? Did the data support Melissa s hypothesis? Use evidence to explain why or why not. If you feel the data were inconclusive, explain why. Although the habitat of the fish was not measured here, the data is consistent with the hypothesis that bold fish were using the riskier open water habitat more, while the shy fish were using the safer cover habitat more. The evidence that the bold fish were larger but had lower survival supports the hypothesis that they take more risks to use the open water habitat. The fish grow faster because they have increased access to food, but they have lower survival because they are more visible to the predators. The evidence that the shy fish were smaller but had higher survival also supports the hypothesis. The shy fish do not take risks, so they hide out in the vegetation. This allows the shy fish to stay safe from the predators but decreases the amount of food they can consume and limits how fast they can grow. Your next steps as a scientist: Science is an ongoing process. What new question do you think should be investigated? What future data should be collected to answer your question? Students may come up with a broad variety of data they would like to collect next. Refer to the Teacher Note below for Melissa s future research plans. 7

8 Teacher Note: Before students answer this section, pause to have a class discussion on the strengths and weaknesses of this study. What can the study tell us about the hypothesis, and what other data would we need to increase our confidence? In this experiment, we assume that survival and growth are determined by the habitats that fish choose to use (based on their personalities). Because bold bluegill died more often and grew faster, this supports the hypothesis that they were using the risky open water habitat that had more food. Because shy fish had higher survival but grew slower, we assume they were using the cover habitat where they were safer from predators but had less food. However, this study alone gave no direct evidence that bold or shy bluegill were in a particular part of the pond. Melissa did not physically observe which habitats the fish were using within the pond. Since this study was conducted, Melissa did more pond experiments to find that bold fish always showed higher growth and somewhat lower survival (not statistically significant, like the results in this Data Nugget). Melissa examined which habitats the fish were using by examining the stomach contents of bold and shy fish. Different types of food (invertebrates and zooplankton) are found in the open water than in the cover habitats. Looking at the different prey found in the fish s stomachs gives a window into the habitat where the fish are eating and spending most of their time. Melissa found that when the bluegill were really small, both bold and shy used the cover habitat. However, when the bluegill were a little larger, the bold fish began to use the open water habitat, but the shy fish did not. Shy fish that were really large did use the open water habitat but not as much as the bold fish that were similar lengths. In the future, Melissa would like to take another approach. She will set up monitoring stations to determine what part of the pond each fish is in. She will inject each fish with a microchip tag, and the monitoring station will record each time an individual fish enters or leaves the cover habitat. This will give Melissa a recording of the habitats where the fish spend their time and how much time they spend in each habitat type. Teacher Note: In a future study, Melissa wants to investigate whether the costs and benefits of bold and shy behavior are fixed or change over time. What happens when the bluegill reach a certain size and are so large that a predator can no longer eat them? She predicts that once they reach a certain age or size, the bold-shy tradeoff disappears and all bluegill will be found out in the open water where there is more food. To have students apply their new knowledge about this study system to a new context, have them work in small groups and consider the following scenario: As young bluegill eat more and more food they grow larger and larger. Eventually they reach a point where they grow too large to fit in the predator s mouth! Once fish predators can no longer eat bluegill, what do you predict would happen to the open water and cover habitat tradeoff? Once bluegill grow larger than the predator s mouth, Melissa predicts the tradeoff between open water and cover habitats will disappear. There would no longer be a cost when using the open water habitat without the threat of a predator, survival would be the same in both habitats. Because bluegill have access to more food in the open water habitat, there would be no need for large bluegill to use the cover habitat. 8