Page 28 - THE MATHMATE November 2024

You try it! Here are two examples with “How to” instructions and an answer key for comparison.
Then, there are four more examples for you to try.

Example 1: Organisms found in the sandy intertidal area of Huntington Beach State Park, SC.

Lower Intertidal Middle Intertidal Upper Intertidal
83% Mollusca 83% Mollusca 2% Mollusca
11% Polychaeta 2% Polychaeta 0.5% Polychaeta
6% Crustacea 15% Crustacea 97.5% Crustacea

Step 1: Mark the x-axis. The x-axis is the distance (in this case, the lower, middle, and upper intertidal
zones of a sandy beach, in order, from lower to upper. There are 3 zones – so divide the x-axis into 3)

Step 2: Mark the y-axis. The y-axis is a list of the groups found along the distance (in this case, the
Mollusca (snails), the Polychaeta (marine worms), and the Crustacea (crabs, shrimp, etc)). There are
3 groups. For they- axis, first count the number of squares you have (here, there are 55) and divide
by the number of groups that you have (here, there are 3). This is the maximum number of squares
you could have per group (here, 55 / 3 = 18.3, which I round to 18 – I want an even, whole, number). I
don’t want to go over 18 squares per group, or I will run out of Y axis space.

Step 3: Now decide how many organisms (in this case, percentages) are represented by each graph
paper square. Take the largest number in your data table (83%) and divide by 2 (83 / 2 = 41.5%).
Mollusks (snails) make up 83% of the organisms in the lower intertidal, so you will need space to
represent 41.5% on either side of (above and below) the group name / midline.

Use this formula: (largest data point / 2) / # squares below midline. You have 18 squares per group, or
9 squares above and 9 below the midline. Take 41.5% and divide by 9 squares below midline; this
gives 4.6 % per square. I will round that up to 5% per square, or, 1 square = 5%.

(If you want a smaller graph, you can recalculate and use 1 square = 10%. With 1 square = 10%, you
will need 5 squares above the group name to represent 41.5 percent, and 5 squares below for the other
41.5 percent. You will need 30 squares on the Y axis for 3 groups, with a midline at 5, 15, and 25).

Step 4: Start drawing the kite. Use this formula: (Data point / 2) / # individuals per square. Here, see
two graphs, one showing 1 square = 5 individuals (Figure 2), and one showing 1 square = 10
individuals (Figure 3). To draw a kite, put points both above and below the midline to correspond with
the number of species. For example, in the Lower Intertidal 83% of the organisms present are
Mollusks. If you start with 1 square = 5 individuals, and with 83% as my largest data point, you will
want to have a point above the midline to show 41.5% (83% / 2 = 41.5%). Now, go to x-axis = Lower;
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y-axis = Mollusca. Since 1 square is 5%, 8 squares will represent 40%, and slightly over the 8 square
(41.5% / 5% per square = 8.3 squares) will represent 41.5%. Place this point just over the 8 square
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up (8.3 squares up), and then place a second point just below the 8 square under the midline (8.3
squares down). Then move to x-axis = Middle, and y-axis = Mollusca. Note that in the middle intertidal,
the organisms are still 83% Mollusks, so you do the same thing. For X = Upper and Y = Mollusca, the
percentage of Mollusca is 2%. Divide 2 by 2 and get 1% for above and 1% for below the midline – and
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1% / 5% per square = 0.2 or 1/5 of a square above and 1/5 (0.2) of a square below. Continue this
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Scctm The MathMate 28 Volume 44/Number 1 October 2024