| Summary: | The strikingly diverse population dynamics of herbivorous small mammals, ranging from high-amplitude, multi-annual cycles to relatively stable dynamics, have puzzled ecologists for a century. Theory predicts that this diversity is shaped by density-dependent food web interactions and stochastic weather events. Recent disrupted cycles through amplitude dampening have been attributed to climate change. However, empirical testing has been hampered by the complexity of the food webs in which these herbivores normally are found. Here we analyze population dynamics of a grazing vole species in a uniquely simple high-Arctic food web without top-down regulation. In accordance with theory, the population dynamics was mostly ruled by overcompensatory density-dependence in winter that without environmental stochasticity would have yielded seasonality driven high-amplitude 2-year cycles. In this simple food web, rain-on-snow events disrupted cyclicity, but not through amplitude dampening. Our case study highlights how food web structure may modify the impact of climate change on population dynamics.
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