Covariation between mean vole density and variability drives the numerical response of storks to vole prey
Hušek et al. (Popul Ecol 55:363–375, 2013) showed that the numerical response of storks to vole prey was stronger in regions where variability in vole density was higher. This finding is, at first sight, in contradiction with the predictions of life-history theory in stochastic environments. Since the stork productivity-vole density relationship is concave, theory predicts a negative association between the temporal variability in vole density and stork productivity. Here, we illustrate this negative effect of vole variability on stork productivity with a simple mathematical model relating expected stork productivity to vole dynamics. When comparing model simulations to the observed mean density and variability of thirteen Czech and Polish vole populations, we find that the observed positive effect of vole variability on stork numerical response is most likely due to an unusual positive correlation between mean and variability of vole density.
KeywordsCoefficient of variation (CV) Jensen’s inequality Life history Population cycles Taylor’s law
We thank Emil Tkadlec for providing us with vole data and comments on the manuscript. John-André Henden, David N. Koons, an anonymous reviewer and the editor provided useful feedback. JH was supported by the BEcoDyn project at Hedmark University College. FB’s postdoc was financed by the ECOCYCLES BiodivERsA project.
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