Snow physical properties may be a significant determinant of lemming population dynamics in the high Arctic

International audience; Cyclic population fluctuations are common in boreal and Arctic species but the causes of these cycles are still debated today. Among these species, lemmings are Arctic rodents that live and reproduce under the snow and whose large cyclical population fluctuations in the high Arctic impact the whole tundra food web. We explore, using lemming population data and snow modeling, whether the hardness of the basal layer of the snow-pack, determined by rain-on-snow events (ROS) and wind storms in autumn, can affect brown lemming population dynamics in the Canadian high Arctic. Using a 7-year dataset collected on Bylot Island, Nunavut, Canada over the period 2003-2014, we demonstrate that liquid water input to snow is strongly inversely related with winter population growth (R 2 ≥ 0.62) and to a lesser extent to lemming summer densities and winter nest densities (R 2 = 0.29-0.39). ROS in autumn can therefore influence the amplitude of brown lemming population fluctuations. Increase in ROS events with climate warming should strongly impact the populations of lemmings and consequently those of the many predators that depend upon them. Snow conditions may be a key factor influencing the cyclic dynamics of Arctic animal populations. Résumé : Des fluctuations cycliques de population sont fréquentes chez des espèces boréales et arctiques mais les causes de ces cycles sont encore débattues. Parmi ces espèces, les lemmings sont des rongeurs arctiques qui vivent et se reproduisent sous la neige et dont les grandes variations de population cycliques dans le haut-arctique impac-tent tout le réseau trophique toundrique. Au moyen de données sur les populations de lemming et de modélisation de la neige, nous examinons la possibilité que la dureté de la couche de neige basale, déterminée par des évènements de pluie sur neige (PSN) et