Estimating the pattern of synchrony in fluctuating populations

Authors


Steinar Engen, Department of Mathematical Sciences, Norwegian University of Science and Technology, N-7491 Trondheim, Norway. Fax: +47 72 55 33 14; E-mail: steinaen@math.ntnu.no

Summary

  • 1A central question in population ecology is how to estimate the effects of common environmental noise, e.g. due to large-scale climate patterns, on the synchrony in population fluctuations over large distances. We show how the environmental variance can be split into components generated by several environmental variables and how these can be estimated from time-series observations.
  • 2With a set of time-series observations from different locations not necessarily covering the same time span, it is shown how the spatial autocorrelation of the residual variance component, not explained by the covariates and corrected for demographic stochasticity, can be estimated using classical multinormal theory.
  • 3Some previous results on spatial scaling in continuous linearized models on log scale are extended to also provide the scaling for the residuals. This is shown to be close to the spatial scaling of the autocorrelation in the environmental noise and only weakly affected by migration.
  • 4The logistic model of local population dynamics with the NAO index as the only covariate is fitted to 22 populations of the Continental great cormorant Phalacrorax carbo sinensis. The spatial scale of the environmental noise is estimated to be about 155 km. The NAO index alone accounts for about 10% of the total environmental variance and nearly all of the regional environmental variance (long-distance environmental autocorrelation).

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