Note: Your answers to the questions below should follow the expectations for homework found here. Questions outside of class can be asked on the Module Assignments-Questions Teams channel (see link on homepage).

Ruffe Feeding

Ogle et al. (2004) examined the diet of larval Ruffe (Gymnocephalus cernuus) in the St. Louis River Harbor, Lake Superior. In one part of their study, they recorded the occurrence (i.e., presence or absence) of six different prey items, plus an “other” category, for Ruffe captured at two locations (Allouez Bay and Whaleback Bay) over six dates. In addition, they recorded the length of the larval Ruffe (in mm). The results of this study are in RuffeLarvalDiet.csv (data, meta). For the questions below, restrict the data set to fish captured just in Allouez Bay (use this for help filtering the data) and focus on the occurrence of Daphnia relative to the length of larval Ruffe. [Note: Be careful to use the o.daph variable.]

  1. Is there a significant relationship between whether or not Daphnia were consumed and the length of the Ruffe? Provide evidence.
  2. Interpret the meaning of the slope. Use a confidence interval.
  3. Interpret the meaning of the exponentiated slope. Use a confidence interval.
  4. Interpret the probability that a 6-mm Ruffe had consumed a Daphnia. Use a confidence interval.
  5. Interpret the odds that a 6-mm Ruffe had consumed a Daphnia. [You don’t need a confidence interval]
  6. What is the length when it is a “coin-flip” whether Ruffe had consumed a Daphnia or not? Use a confidence interval.
  7. What is the length where nearly all (90%) of Ruffe had consumed a Daphnia? Use a confidence interval.
  8. Construct a plot that shows the best-fit logistic regression line with a confidence band.