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Title: What techniques can scientists use to obtain population estimates?
Principle(s) Investigated: Statistical analysis, population dynamics
Standards:
Science and Engineering Practices:
Developing and Using Models, Analyzing and Interpreting Data, Using Mathematics and Computational Thinking, Constructing Explanations and Obtaining, Evaluating and Communicating Information
Cross Cutting Concepts:
Scale, Proportion and Quantity, Systems and Systems Models
Ultimately, this procedure is one component that will lead to:
HS-LS2-7: Design, evaluate and refine a solution for reducing the impacts of human activities on the environment and biodiversity.
Materials:
100 blue or black beads and 100 white or yellow beads per every 4 students
1 Tray for every 4 students
1 Plastic cup for every 4 students
1 Handout for every 4 students
Procedure:
Pass out supplies to students and explain the activity. Students should follow directions on handout and record their data on the provided worksheet. The instructions are as follows:
1. Catch some fish! With one hand, grab a handful of “fish.” Count how many you have and write the number below.
2. “Mark” these fish by replacing them with a white/yellow bead and putting them back into the pond. (The blue/black beads don’t go back in)
3. Mix the beads to make your fish swim!
4. Catch some more fish! Count all of the fish you caught and write the number below.
5. Count the number of marked fish you caught in your second catch. Write the number below.
The students then perform the calculations on the worksheet and answer the analysis questions. Following this, you can lead a discussion based on the analysis questions.
Student prior knowledge: Multiplication, division, order of operations, vocabulary: estimate, population.
Explanation: In this activity, students are able to evaluate a statistical survey technique used to determine population sizes. However, when conducting such a survey, there are many opportunities for error, such as fluctuation in population size, learned fish behavior (fish that have been caught once are less likely to be caught a second time), or having an initial sample size that is too small to provide accurate results. There are techniques to help mitigate these errors, such as averaging data repeat catch and mark surveys rather than just relying on one. In this activity, students are asked to not just calculate the answers, but to provide explanations for anomalous data, possible sources of error and suggestions for improving this technique.
Questions & Answers:
1. What are some sources of error for this technique?
Small original sample size, increases or decreases in population between initial catch and secondary catch, fish already
caught previously becoming wary of catching techniques.
2. How would fish surveys vary in different ecosystems or different types of fish?
In some ecosystems, this method might not be practical, such as open ocean, where fish populations travel over large
spaces. Some fish types remain in one spot for long periods of time, where direct counts are possible.
3. Why do scientists need to conduct fish population surveys?
To determine where to apply conservation efforts or to provide data for fishery regulations, to name two examples..
Applications to Everyday Life:
Understanding statistical estimates can be beneficial, as we evaluate statistical claims on a daily basis. This may include when we make health choices, when we hear about polls, or when encountering advertisements.
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