Georgian Court University
“The Plot Thickens”: Using Quadrats to Estimate Abundance and Densities of Organisms
Grade Level: 6-8
Time Frame: 2 - 3 class periods
Introduction to Lesson:
In this lesson students will continue to review the concept of using symbols to represent real-world objects or organisms. However, the focus of the application is now on using quadrat estimation to count the numbers of individuals within a population. Students will also work with enumerating the number of kinds of organisms, estimating their abundance and density, as well as reviewing the use of percentages in the context of community composition. They will use these skills to assess the effects of a Phragmites invasion into a hypothetical ecosystem.
New Jersey Core Curriculum Content Standards
STANDARD 4.1 (Number and numerical operations) All students will develop number sense and will perform standard numerical operations and estimations on all types of numbers in a variety of ways.
A. Number Sense
o Explore the use of ratios and proportions in a variety of situations.
STANDARD 4.2 (Geometry and measurement) All students will develop spatial sense and the ability to use geometric properties, relationships, and measurement to model, describe and analyze phenomena.
D. Units of Measurement
E. Measuring Geometric Objects
· Develop informal ways of approximating the measures of familiar objects (e.g., use a grid to approximate the area of the bottom of one's foot).
STANDARD 4.4 (Data analysis, probability, and discrete mathematics) All students will develop an understanding of the concepts and techniques of data analysis, probability, and discrete mathematics, and will use them to model situations, solve problems, and analyze and draw appropriate inferences from data.
A. Data Analysis (or Statistics)
· Collect, generate, organize, and display data.
· Read, interpret, select, construct, analyze, generate questions about, and draw inferences from displays of data.
· Range, median, and mean
STANDARD 3.1 (Reading) All students will understand and apply the knowledge of sounds, letters, and words in written English to become independent and fluent readers, and will read a variety of materials and texts with fluency and comprehension.
A. Concepts About Print/Text
Use a glossary independently and appropriately.
C. Decoding and Word Recognition
Apply knowledge of new words correctly
STANDARD 3.5 (Viewing and media literacy) All students will access, view, evaluate, and respond to print, nonprint, and electronic texts and resources.
Respond to and evaluate the use of illustrations to support text.
Identify the central theme in a movie, film, or illustration.
Materials and Resources:
Show students the PowerPoint slides of marshes (provided). Engage students in a discussion of what they see. Guide them to observe differences in (1) the number of different kinds of plants present and (2) the number of plants present (density). Ask them to imagine that they’ve been assigned to find out how many of each type of plant is present within each of the marshes. How long do they think it would take them to count all of the plants of each type within the marsh? Once it becomes clear that there are too many to count easily, ask the students “how else could they find the answer?” Hopefully the students will come up (can be guided to) the idea of counting smaller “representative” areas and then “extrapolating” from those to the larger marsh. The teacher can then show students the final two slides in which scientists are shown carrying a quadrat to a marsh and then using it to count the different kinds of plants within the designated area. Point out that the scientists must first identify the plant types and then count (enumerate) the number of each type within the area delineated by the quadrat. The teacher will then lead the students to a discussion on how, once one has an estimate of the numbers and types of organisms within a set of quadrats, these numbers could be used to develop and estimate an estimate of what are the typical (or “average”) values for the numbers and types of species in this marsh? (Hopefully once the students hear the substitution of the word “average” for the word “typical” this will prompt they to offer the idea of computing an average or mean for each plant type / quadrat. Finally, ask the students if they know the average number of plants per quadrat for a marsh, and the marsh’s area is 100x that in the quadrat, how many plants would they expect (approximately) would there be in the whole marsh. Then ask, if the marsh’s area was some other number of times larger than that sampled within the quadrat, how would they work out how many plants (total) were in the marsh? Once the students have seen the pattern that the total number of plants in the marsh can be approximated by working out what fraction of the marsh’s area is represented within the quadrat and then multiplying the “typical” or average number of plants within the quadrat by that amount, they can estimate the total number of each plant type within the larger marsh area.
1. Each group of students will be provided with a set of posters representing a marsh in New Jersey and a set of “quadrats” (transparent plastic squares with cardboard frames).
2. Students will be asked to locate the legends. The teacher will then review with the students the type of plant represented by each symbol.
3. Students will then be given two minutes to brainstorm in their group for a good way to place their quadrats onto the “map” in such a way as to create representative “replicate” measurements of the kinds of plants within the marsh. Ideal strategies would involve either some degree of randomness (e.g. throwing the quadrat with one’s eyes closed), or strategies that employ a variant of a “systematic” sampling design (e.g. (1, 1), (2,2), (3,3) within an imagined grid system superimposed on the marsh, where (1, 1) would be 1 quadrat unit from the left and 1 quadrat unit from the top).
4. Students will be asked to share their group’s strategy with their classmates. This will allow the teacher to assess the suitability of the suggested strategies, as well as providing groups who had struggled with this concept with guidance on how to achieve this. With the help of the teacher the class will either pick a single strategy or agree on a suite of acceptable strategies which can be used in sampling. Ideally students in one group should NOT sample exactly the same plots within each marsh as those in other groups sampling the same marsh, since later on we want students to see that they all get slightly different answers to the same questions as a result of the locations of their subset of quadrats. This isn’t a problem if a random sampling design is employed, but if students use a systematic approach the teacher should encourage use of different patterns within each group so that a different subset of quadrats is counted within each marsh.
5. Students will then make at least 10 replicate quadrat samples from their “native marshes” and enter the data into the table provided and make a variety of calculations (column averages, estimates of biodiversity)
6. Students will then repeat this exercise for each model marsh (at different stages of invasion), recording the same data for each one. (To save time the teacher may wish to assign different groups to collect data from marshes at different stages in the invasion. However, there should be some overlap (more than one group assessing diversity and densities for each marsh) to allow later discussion of why different groups got different answers even though they had sampled the same marsh).
7. The number of different kinds (species) of organisms within an area is known as biodiversity. Students will assess the biodiversity of the various model marshes by counting the number of KINDS of plant present in each replicate quadrat for each model marsh assessed.
8. Students will report their findings on biodiversity for each quadrat that they measured, and the teacher will tally the results on the board or a chart so that all students can see the results from all groups.
9. What is the range of values for biodiversity seen within quadrats in each model marsh?
10. What is the mode for the data set on biodiversity in the quadrat samples from each marsh model?
11. What is the median number of kinds (biodiversity) that was seen in the quadrats from each marsh model?
12. Students will compute the mean (average) of their counts of the number of kinds (biodiversity) of plants within each quadrat for each model marsh assessed.
13. The students will then tally the number (abundance) of individuals of each kind of plant within each quadrat for each of their assigned model marshes
14. Students will calculate density (number of stems per square meter) for different plants within their quadrats for each of their assigned model marshes
15. Students will calculate the average density of each plant type within the quadrats sampled for each of their assigned model marshes.
16. Students will calculate the fraction and percentage of each kind of plant within the community for each of their assigned model marshes
17. Students will calculate the total area of the marsh (the poster)
18. Students will calculate the ratio of their quadrat size to that of the total size of the marsh (i.e. what fraction of the marsh area is represented within one quadrat?)
19. Students will use this information to extrapolate from their average counts for each plant type quadrat samples to the overall marsh in order to calculate how many plants of each species and in total are present in the marsh at each stage in the invasion
20. Students will be asked to select a “spokesperson” who will report their groups’ calculated densities for several key species (requested by the teacher) at a given stage within the invasion to the class. Teacher will tally these results on the board, chart or similar so that the answers for the different groups can be seen side by side for the different species and stages of invasion requested. Assuming all went well, the estimates provided from the different groups should be similar, but often will not be identical. Encourage students to discuss why this might be and what this means for the accuracy of their estimates. In particular, students may observe that variability is particularly high for relatively rare species. Encourage students to speculate on why this might be.
Note: Data from the quadrat samples taken in this lesson plan will be used again in several succeeding lessons. Remind students to put the data somewhere safe and to be sure that they bring it to all subsequent classes. (Teacher may want to collect copies of all data generated in this class, just in case it gets lost and needs to be provided to the students again when the next need it).
Accommodations and Modification:
· Group students into groups such that each group has a mix of students with different learning styles and strengths.
· Group students such that each group has a mix of students with different learning styles and strengths.
· Provide students with visual impairment with alternative visual media (printouts of PowerPoint slides, graphs made with puffy pens or embossing) to allow them to participate in the games
· If needed, pair students so that one student can read directions aloud to another
· Provide handouts and worksheets with larger font sizes, raised or embossed writing, or Braille for visually impaired students
Closure / Homework
Have students discuss within their groups and then report back to the class on one of the following questions (teacher should assign questions to groups). Alternately, have students write a paragraph on one or more of the following for homework.
3. What do you think the marsh would look like if you could visit it and walk around in it at different times within the invasion? What would you see? How hard would it be to move through the vegetation in the marsh (don’t worry about sinking in the mud… you have special shoes on that prevent this. We’re just talking about how it would be to move through the plants here)?
4. What do you think the marsh would feel like to an animal that fed on / nested in one of the native plants present before the invasion as the Phragmites invasion takes place? What would this mean for those animals?
5. If reinforcement of graphing formats is desired, provide students with additional data sets and ask them
a. What is the appropriate graph format for data of that type and why?
b. Create the graph for each data set using the format that you’ve identified.
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© 2009. Louise Wootton. Edited by Claire Gallagher
Although the information in this document has been funded wholly or in part by the United States Environmental Protection Agency under assistance agreement NE97262206 to Georgian Court University, it has not gone through the Agency's publications review process and, therefore, may not necessarily reflect the views of the Agency and no official endorsement should be inferred.