Power Analysis of Wolf-Moose Functional Responses

Gray wolf (Canis lupus) predation is density dependent if the proportion of prey killed by wolves increases wit h prey density. The functional response is 1 component of wolf predation that has important effect on whether density-dependent predation occurs, and consequently whether wolves have the potential to regulate prey to a low-density equilibrium. Because the functional response alone may determine if predation is regulatory, researchers have been attempting to accurately describe the functional response for wolves. We used simulated datasets based on the typical variances found in wolf-moose (Alces alces) predation data to evaluate the sample size required to distinguish between 2 common forms of wol f functional response: Type II and Type III. We found that we required sample sizes considerably larger than those likely attainable for wolf-moose predation studies. This conclusion was true even for a strongly sigmoid functional response (C > 2 in the Michaelis-Mento equation). Our analysis suggests it would be better to devote more effort toward measuring total predation losses versus trying to determine the shape of the functional response.