Réponse numérique de l'hermine aux fluctuations d'abondance de Microtus pennsylvanicus

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Abstract
The numerical response of 2 ermine populations (Mustela erminea) to the density fluctuations of the meadow vole (M. pennsylvanicus), the domiant mammal in southern Quebec [Canada] agrosystems, was studied from 1978 to 1980. There is a strong correlation between the densities of the 2 spp., whether or not the fluctuations of Microtus are cyclical. Males and females show a different response: the numerical adjustment of males is strongly correlated to the fluctuations of the vole population; the females do not seem to make particular adjustments. The numerical response of the ermine takes place only a few months after the changes in the rodent population. In areas where prey are small and of similar size the survival of the females is less dependent than that of the males on the density of the dominant prey. As most female ermines seem to participate in reproduction whatever the density of the vole population, the continuity of any local population is insured from year to year by the presence of at least minimal numbers. Survival of the young during the year following their birth seems to depend on the immediate availability of prey, thus determining the characteristics of the numerical response.