Demography during a population crash of the wood lemming, Myopus schisticolor

Abstract

Four-year microtine population density cycles are extreme in northern Fennoscandia. We studied populations of wood lemmings (Myopus schisticolor) and bank voles (Clethrionomys glareolus) in the peak phase and subsequent crash phase at two localities, Varaldskogen and Risberget, Norway. Bank voles at Varaldskogen and bank voles and wood lemmings at Risberget crashed during the nonreproductive period in winter when we were not trapping animals. Wood lemmings at Varaldskogen, however, crashed during the reproductive period in summer. Reproduction in the wood lemming population was as intense during the summer crash as in the peak phase. Further, survival of overwintered animals was the same in peak populations and in the population undergoing the crash. However, lack of recruitment was the cause of the summer crash of the wood lemming population. Poor nutrition is the most likely cause of the lack of recruitment.