An article in Oikos: A Journal of Ecology, “Regulation of Root Vole Population Dynamics by Food Supply and Predation: A Two-Factor Experiment,” (Vol. 109, 2005, pp. 387–395), investigated how food supply interacts with predation in the regulation of root vole (Microtus oeconomus Pallas) population dynamics. A replicated two-factor field experiment manipulating both food supply and predation condition for root voles was conducted. Four treatments were applied: -P, +F (no-predator, food-supplemented); -P, -F (predator-access, food-supplemented); +P, +F (no-predator, non-supplemented); P, F (predator-access, food-supplemented). The population density of root voles (voles ha1 ) for each treatment combination in each follows.
(a) What is an appropriate statistical model for this experiment?
(b) Analyze the data and draw conclusions.
(c) Analyze the residuals from this experiment. Are there any problems with model adequacy?