A gradient from stable to cyclic populations of Clethrionomys rufocanus in Hokkaido, Japan
Proceedings of the Royal Society of London B (1996) 263:1117-1126
Thirty-one years of abundance data from ninety populations of the grey-sided vole (Clethrionomys rufocanus) in northern Hokkaido (Japan) were analysed with respect to population dynamic characteristics. Both non-periodic and multi-annually periodic fluctuations occur among the studied populations. The length of the period varies from 2 to 5 years. The dynamics appear approximately linear on a logarithmic scale, and a log-linear stochastic difference model with one time-lag is found to recreate the periodograms of the time series. The deterministic (log-linear) component of these models determine the periodicity while stochasticity sustains the cycles. The dynamics of the Hokkaidian vole populations are found to vary clinally from the western coast eastwards and towards the interior of the study area. This gradient corresponds superficially to the latitudinal gradient seen in microtine populations in Fennoscandia. However, under close scrutiny, these gradients differ greatly: the Hokkaidian gradient is due to a cline in delayed density-dependence. Statistical delayed density-dependence is more negative towards the east and the interior.
Key words: Comparative population dynamics; Stochastic difference equations; Rodents; Autoregressive time series analysis; Direct and delayed density-dependence.