Statistical Ecology
Stat 555, Fall 2009

 Randomized Blocks
Assignment #3

rock boring urchin

Problem:  Importance of habitat for rock-boring urchins in Hawai`i

To investigate the importance of rocks as shelter for rock boring urchins (Echinometra mathaei) an experiment was conducted in two areas in a nearshore lagoon near Hilo, Hawai`i.    

Previous field projects have shown that urchins are more abundant where rocky areas are present and they tend to be individually attracted to rocks. Because predation on urchins may vary in space the study was conducted at two separate areas (transects) which were used as a randomized blocks.

Experimental Procedure:

  1. A team of students were assigned randomly to each of three experimental treatments: control, manipulation, and manipulation control.
  2. The field procedure for conducting the experiment consisted of the following steps:

i) Two transects were positioned in the shallow area (1 m) of the lagoon ("the study area") and extended for 30 meters. They served as blocks in the experiment.

ii) Before entering the water, each small group generated 10 random numbers between 0-30.

iii) First survey: each team located the meter coordinate on the transect indicated by the random number and positioned the quadrat at this coordinate:

CONTROL:

  • Counted the total number of urchins contained in each of 10 quadrats.

EXPERIMENTAL

  • Counted the total number of urchins contained in each of 10 quadrats.
  • After recording the data small rocks were removed from the quadrat, attached urchins were scraped off into the quadrat, and rocks were removed from the quadrat to the left side of the transect.

EXPERIMENTAL CONTROL

  • Counted the total number of urchins contained in each of 10 quadrats.
  • After recording the data small rocks were removed from the quadrat, attached urchins were scraped off into the quadrat, and the rocks were replaced in the quadrat (not on top of the urchins!).

iv) 20-30 minutes was allowed for urchins to respond to their changed environment

v) Second survey: the surveys were repeated using the same coordinates as before with each group recording the total number of urchins in each quadrat. A change in abundance was calculated as the difference between the before and after counts.

vi) Steps i through v were then repeated by the same three teams at a different transect in the same area.

Assignment

The data are entered into Excel (Wana Experiment2.xls). Copy the data into MINITAB and conduct the following analyses.

  1. Create a statistical model for the problem and develop null and alternate hypotheses from the model.

  2. Test the data for meeting the assumptions of ANOVA and transform if needed.

  3. Analyze the data using an ANOVA

  4. Interpret the results both statistical and biologically. Think critically about the design of the study, the results, and how it might be improved through design and/or analysis.

This assignment is due on Wednesday, Sept 23 in class