Moose and deer resource selection and co-occurrence in northeast Minnesota

Abstract

A parasite, Parelaphostrongylus tenuis, carried by white-tailed deer (Odocoileus virginianus) has often been cited as a significant factor contributing to moose (Alces alces) population declines. Moose suffer from neurologic disease and usually die when infected with P. tenuis. The strength of the three-way relationship between moose, deer, and P. tenuis, and the resulting negative impact on moose health, is thought to be driven by deer densities. Despite its importance for moose and deer management, only one peer-reviewed study to date has tested the relationship between deer and moose densities, and therefore the potential for parasite-mediated competition between moose and deer, using empirical data. A deer density threshold above which moose populations declined was identified using the empirical data collected for the study. However, the nature of the data and apparent outliers suggest that the modeling approach used to develop that threshold may not have been appropriate. Here we tested, using data from the original study, whether alternative models, including linear models and negative binomial models would be less sensitive to outliers and could better explain the relationship between deer and moose densities in this study system. We found no evidence in our analysis that moose density decreases as deer density increases. We conclude that while the proposed moose-deer-P. tenuis relationship could be partially density dependent, additional factors such as frequency dependence of disease transmission and shared use of resources by moose and deer should also be considered.