Locating samples

(30 points)

In this exercise, you will practice locating random samples as if in the field, using three methods — finding quadrat locations using Cartesian coordinates, finding quadrat locations using the grid system, and selecting random individuals. Take the role of a crew supervisor, preparing field procedures for crew members.

Procedure

Download the diagrams.  One diagram is a 12-cm by 18-cm rectangle representing a 50-m × 75-m study area.  The other diagram depicts a woodland study area. Then either fire up the random-number generator on your calculator or computer, or print the random number table file from the chapter.

(Hint  about printing the diagrams: When you print the PDF file, change the "Print Scaling" option from "Reduce to Printer Margins" to "None."  Otherwise the diagram will not be a 12-cm by 18-cm rectangle.)

In the 50-m × 75-m study area, use Cartesian coordinates to pick five locations at random for five quadrats of size 5-m × 10-m. Draw in the quadrat to scale at each location.

In the 50-m × 75-m study area, use the grid system to pick five 5-m × 10-m quadrats at random, drawing quadrats from a grid of locations.

In the woodland study area, pick five individual trees at random from the population of all trees (visible) within the study boundary.

Report

  1. Explain how you generated random numbers.
  2. Explain your procedure for going from random number to quadrat location or tree. Explain your rules for dropping unsuitable random numbers (even if you didn't have to drop numbers).
  3. Show the random numbers you used to select quadrats and trees, and any random numbers you discarded as unsuitable.
  4. Include a copy of your study-area diagram showing the locations of your quadrats and trees.
  5. Make sure the diagram of the 50-m × 75-m study area is labeled well enough to orient your crews in the field.
  6. For BOT 540 students: Discuss how well or poorly interspersed the quadrats were using the two procedures.

This exercise is not as easy as it might seem. Refer to the chapter for guidelines for dealing with real-life complications, such as how the quadrat sits with respect to the random location, whether you sample with replacement, and what happens if a quadrat extends beyond the edge of the study area.

(Page limit: 1 single-spaced page, not including diagrams)

 

Version: June 22, 2007