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Why spacing behavior does not stabilize density in cyclic populations of microtine rodents
Authors:Edward J Heske  Søren Bondrup-Nielsen
Institution:(1) Department of Biology, University of New Mexico, 87131 Albuquerque, NM, USA;(2) Department of Biology, Division of Zoology, University of Oslo, Blindern, P.O. Box 1050, 0316 Oslo 3, Norway;(3) Present address: Department of Biology, Acadia University, BOP 1X0 Wolfville, Nova Scotia, Canada
Abstract:Summary There are several published hypotheses that consider spacing behavior to be a significant factor causing the multiannual density fluctuations characteristic of some microtine rodent populations. Recent modeling efforts have concluded, however, that spacing behavior should have a stabilizing rather than a destabilizing effect on population dynamics. Why doesn't spacing behavior stabilize these cyclic populations? We argue that while spacing behavior does have a stabilizing influence on population dynamics by limiting the number of breeding individuals, reproduction continues and population size is not limited in an asymptotic manner. Rather, microtine social organization produces demographic changes within a population that allow density cycles to occur under certain conditions. Using a simulation model, we demonstrate that in a strongly seasonal environment populations with low density dependence in reproduction will cycle whereas populations with high density dependence in reproduction will have relatively stable densities. Given such complicating factors as the ldquoannual speciesrdquo nature of microtine rodents, occasionally intense predation, and the tendency for territoriality to break down during the non-breeding season, individuals with low density dependence in reproduction will always be able to invade and eventually dominate populations with high density dependence in reproduction, regardless of the resulting destabilization of population dynamics.
Keywords:Spacing behavior  Vole cycles  Microtus  Density dependence  Intraspecific competition
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