Predators and Small Rodent Cycles: An Analysis of a 79-Year Time Series of Small Rodent Population Fluctuations

Abstract

We analyse a 79-yr time series of small rodent peak years from South-East, Central, North Norway by a statistical method for detecting cyclic patterns in sequences of binary numbers. We demonstrate that the populations of small rodents, which usually have been considered to exhibit exclusively cyclic dynamics in these regions, lost their cyclicity during a period of approximately 20 yr at the beginning of this century. During their cyclic phases the small rodent populations fluctuated synchronously within each of the geographic regions and between South-East Norway and Central Norway. But North Norway was out of phase with the two southern geographic regions. A reduction of the total number of small rodent predators, as a result of a country wide predator extermination programme initiated around 1900, may have produced the changes in the small rodent population dynamics as well as a dramatic increase in the population of several small game species.