Moose-wolf dynamics and the natural regulation of moose populations

Long term data indicate that naturally regulated moose populations in southwestern Quebec stabilize at a density of ≈ 0.40 animal-km⁻². To test population regulation by forage competition, moose body condition was investigated near this equilibrium density (0.37=H) and at 2 lower densities (≈0.23=M, 0.17=L). Measurements of head length, cranial breadth, heart weight, and kidney weight were collected from 443 moose killed during the autumn harvesting seasons of 1981 and 1982. There was no indication that body condition was poorer at the high moose density, and hence no evidence that competition for forage explains the regulatory process. To test population regulation by predators, moose-wolf dynamics were studied at the same 3 moose densities (partial data in area L). In areas H and M, packs averaged 5.7 and 3.7 individuals, year-long territory sizes averaged 390 and 255 km2, and interstices between territories represented ≈0% and 30% of the available area, respectively. The wolf population in area M, as compared to area H, suffered from a higher mortality rate due to malnutrition and lethal intraspecific combat, and from a lower success in producing pups. Analysis of summer scats and winter feeding observations indicated a greater use of alternative food resources at lower moose densities. Each pack killed on average 5.3, 1.8, and 1.1 moose 100 days in areas H, M, and L, respectively. January wolf densities were respectively 1.38, 0.82, and 0.36 animals 100 km⁻². Year-long predation rates proved to be density-dependent, increasing with moose density from 6.1 to 19.3% of the postnatal populations. I conclude that moose populations in southwestern Quebec are regulated by predators at a density where competition for forage offers no detrimental effect. Preliminary results of a wolf removal experiment in area H support this hypothesis. A review of the natural regulation of moose populations is presented. I support the concept that wolf predation can have an important regulatory effect at low moose densities (