Chaos in microtine populations

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Abstract
On the basis of nonlinear time-series analysis of vole data, Turchin (1993) proposed that there is a latitudinal shift from stability to chaos in the dynamics of vole populations. Falck et al. (1995) question several aspects of the approach I used. In particular, they point out that no measure of uncertainty has been calculated for each point estimate of the dominant Lyapunov exponent (a positive Lyapunov exponent implies chaos, while a negative one implies stability). In this note I respond to the criticisms of Falck et al. (1995). As part of my response, I analyse fluctuations of pooled numbers of microtine rodents at all European locations for which I currently have data. Treating each geographic location as a replicate, I show that the mean Lyapunov exponent is significantly greater than zero in northern populations (latitude greater than 60 degrees N).