Plugging space into predator-prey models: an empirical approach.
Englund, Göran*,1, Bergström, Ulf 2, Leonardsson, Kjell1, 1 Department of Ecology and Environmental Sciences, Umeå, Sweden2 National Board of Fisheries, Öregrund, Sweden
ABSTRACT- Extrapolating ecological process functions from small-scale experimental systems to scales of natural populations usually entails a considerable increase in spatial heterogeneity, which may affect process rates and, ultimately, population dynamics. We demonstrate how information on the heterogeneity of natural populations can be taken into account when scaling up laboratory derived process functions, using the technique of moment approximation. We apply moment approximation to a benthic crustacean predator-prey system, where a laboratory derived functional response is made spatial by including correction terms for the variance in prey density and the covariance between prey and predator densities. We also show how moment approximation may be used to incorporate spatial information into a dynamic model of the system. While the non-spatial model predicts stable dynamics, its spatial equivalent also produces bounded fluctuations, which agrees with the observed dynamics. A detailed analysis shows that predator-prey covariance, but not prey variance, has a destabilizing effect on the dynamics. We conclude that second-order moment approximation may provide a useful technique for including spatial information in population models. A major advantage of the method is its conceptual value - by providing explicit estimates of variance and covariance effects, it is possible to visualize how heterogeneity affects ecological processes.
Key words: functional response, moment approximation, extrapolation, spatial heterogeneity
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