The Cumulative Effect of Consecutive Winters' Snow Depth on Moose and Deer Populations: A Defence

Abstract

L. D. Mech et al. presented evidence that moose Alces alces and deer Odocoileus virginianus population parameters are influenced by a cumulative effect of three winters' snow depth. They postulated that snow depth affects adult ungulates cumulatively from winter to winter and results in measurable offspring effects after the third winter. F. Messier challenged those findings and claimed that the population parameters studied were instead affected by ungulate density and wolf indexes. This paper refutes Messier's claims by demonstrating that his results were an artifact of two methodological errors. The first was that, in his main analyses, Messier used only the first previous winter's snow depth rather than the sum of the previous three winters' snow depth, which was the primary point of Mech et al. Secondly, Messier smoothed the ungulate population data, which removed 22-51% of the variability from the raw data. When we repeated Messier's analyses on the raw data and using the sum of the previous three winter's snow depth, his findings did not hold up.