The Acorn Lab

1
The Acorn Lab

• BIOL 3500L
• Ecology Laboratory

2
Learning Objectives

• Use and correctly read Vernier calipers
• Construct
• Frequency distribution
• Histogram
• Scatter plot
• Calculate
• Mean
• Variance
• Std. deviation
• Std. error of the mean
• Determine
• The precision of an instrument (such as calipers)

3
Calculators

• Always bring a calculator to lab
• Cheap is great!!!
• No need for fancy functions!!!
• No need for graphing capabilities

4
Precision

• Precision ability to measure small increments
• How to determine precision
• The markings on a beaker
• 25 ml beaker vs. 100 ml
• The decimal places on a balance
• Truck scale vs. triple beam balance
• Timepieces
• Clock vs. stopwatch

5
Vernier Calipers

• Allow for tiny measurements
• Cheaper and more robust than dial calipers
• Practice with websites
• Vernier Website 1
• Vernier Website 2
• Vernier Website 3

6
Frequency Distribution

• An organized, summarized list of measurements
• Tells number within each interval
• Ex Ages of people in a group

7
Frequency Distribution Example

• Bluegills (cm) 8.83, 9.25, 8.77, 10.38, 9.31,
  8.92, 10.22, 7.95, 9.74, 9.51, 9.66, 10.42,
  10.35, 8.82, 9.45, 7.84. 11.24, 11.06, 9.84, 10.75

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Histogram
9
Scatter Plot
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Mean

• Mean average
• Not the only measure of centrality!
• Also median and mode!
• Example
• Bluegills (cm) 8.83, 9.25, 8.77, 10.38, 9.31,
  8.92, 10.22, 7.95, 9.74, 9.51, 9.66, 10.42,
  10.35, 8.82, 9.45, 7.84. 11.24, 11.06, 9.84, 10.75

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Mode

• Mode most common number
• Bluegills (cm)
• 8.83, 9.25, 8.77, 10.38, 9.31, 8.92, 10.22, 7.95,
  9.74, 9.51, 9.66, 10.42, 10.35, 8.82, 9.45, 7.84.
  11.24, 11.06, 9.84, 10.75
• Question Do the bluegills have a true mode
• Do they have a mode if we round down?

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Median

• Median the middle one (for odd sample size)
• Or average of the two in the middle for even
  sample size

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Variance, Standard Deviation, SEM

• See Quantifying Ecology 2.1 in your text