Get access

Bootstrap methods for estimating spatial synchrony of fluctuating populations

Authors

  • Magnar Lillegård,

  • Steinar Engen,

  • Bernt-Erik Sæther


M. Lillegård and S. Engen, Dept of Mathematical Sciences, Norwegian Univ. of Science and Technology, NO-7491 Trondheim, Norway (magnarl@math.ntnu.no). – B.-E. Sæther, Dept of Biology, Norwegian Univ. of Science and Technology, NO-7491 Trondheim, Norway.

Abstract

We describe and examine methods for estimating spatial correlations used in population ecology. We base our analyses on a hypothetical example of a species that has been censured at 30 different locations for 20 years. We assume that the population fluctuations can be described by a simple linear model on logarithmic scale. Stochastic simulations is utilized to check how seven different ways of resampling perform when the goal is to find nominal 95% confidence intervals for the spatial correlation in growth rates at given distances. It turns out that resampling of locations performs badly, with true coverage level as low as 30–40%, especially for small correlations at long distances. Resampling of timepoints performs much better, with coverage varying from 80 to 90%, depending on the strength of density regulation and whether the spatial correlation is estimated for the response variable or for the error terms in the model. Assuming that the underlying model is known, the best results are achieved for parametric bootstrapping, a result that strongly emphasize the importance of defining and estimating a proper population model when studying spatial processes.

Ancillary