Relationship between El Nino/South Oscillation (ENSO) and population outbreaks of some lemmings and voles in Europe

Ecologists have been puzzled by population cycles of lemmings and voles for the over 70 years. At present, our understanding and explanation to this p henomenon remain controversial. Recently, El Nino/South Oscillation has att racted attention of ecologists on its links with population outbreaks of te rrestrial animals. This paper aims to investigate the statistical relations hip between outbreaks of microtine rodents and ENSO events by scanning avai lable literature. During 1862-1894, outbreaks of Norway lemmings in Norway tended to occur in the Southern Oscillation Index (SOI) peak years or 1 yea r after the SOI peak years with an approximate significance level (p = 0.05 7). During 1885-1931, outbreaks of voles in France tended to occur 1 year b efore the SOI peak years (p = 0.01). During 1946-1993, outbreaks of lemming s and voles in North Finland tended to occur 1 year before the SOI peak yea rs with a significant level (p = 0.022); the peaks of population abundance corresponded well to the SOI trough years (equal to I year before the SOI p eak years). Outbreaks of common voles in Poland during 1946-1975 tended to occur in the SOI peak years or 1 year before the SOI peak years (p = 0.011) , and also tended to occur I year before the SOI peak years (p = 0.030). It was also found that the rodent outbreaks in Norway and France, rodent outb reaks in Finland and Poland synchronized well. It was suggested that the EN SO-related climate or food were key factors in causing outbreaks of microti ne rodents in Europe.