Population structure, distribution, and demography of muskrats during the ice-free period under contrasting water fluctuations

Abstract

Abstract:We tested experimentally four predictions related to the hypothesis that water level limits population size and distribution of muskrats during the ice-free period. The following three predictions were supported: (1) population growth rate was affected negatively by extreme fluctuations in water level, (2) the relative distribution of dwellings among habitats was dependent on water-level conditions, and (3) adult survival and juvenile recruitment were lower under variable than constant water level, particularly in marginal habitats. We postulated that the nutritional condition of muskrats during the breeding period would be unaffected by water level regime due to continued access to food resources. However, individuals that experienced severe water fluctuations possessed an average of 5% less fat than individuals that experienced constant water level, thus falsifying our fourth prediction. These results suggest that (1) water level strongly limits population size of muskrats, and (2) spacing beha...