Asynchronous population dynamics of Siberian lemmings across the Palaearctic tundra

The synchrony of Siberian lemming (Lemmus sibiricus L.) population dynamics was investigated during a ship-borne expedition along the Palaearctic tund ra coast in the summer of 1994. On 12 sites along the coast from the Kola P eninsula to Wrangel Island, relative densities of lemmings were recorded us ing a standardised snap-trapping programme. The phase position of the lemmi ng cycle in each of the studied populations was determined based on current density estimates, signs of previous density and the age profile of each p opulation (ageing based on eye lens mass). In addition, dendrochronological methods were used to determine when the last peak in the density of microt ine populations occurred at each site. The examined lemming populations wer e in different phases of the lemming cycle. Some populations were in the pe ak phase, as indicated by high current densities, an age profile in which o lder individuals were well represented, and signs of high previous density (abundant old lemming faeces). Other populations were in the decline phase, as reflected in a moderate current density, a predominance of older indivi duals and signs of high previous density. Populations in the low phase had an extremely low current density and showed signs of high previous density, while populations in the increase phase had a moderate current density, a predominance of younger individuals and showed signs of low previous densit y. The results of phase determinations based on dendrochronological methods support the findings based on lemming demography. Recent Russian studies c arried out on some of the sites also agreed with our phase determination re sults. Thus, on a regional scale (across the whole Palaearctic tundra), the population dynamics of Siberian lemmings can be considered asynchronous. H owever, sites situated adjacent to each other were often phase synchronous, suggesting a more fine-grained pattern of dynamics with synchrony over dis tances as long as 1000 km or so, e.g. the Yamal and Taymyr Peninsulas.