Taking the beat of the Arctic: are lemming population cycles changing due to winter climate?

Reports of fading vole and lemming population cycles and persisting low populations in some parts of the Arctic have raised concerns about the spread of these fundamental changes to tundra food web dynamics. By compiling 24 unique time series of lemming population fluctuations across the circumpolar region, we show that virtually all populations displayed alternating periods of cyclic/non-cyclic fluctuations over the past four decades. Cyclic patterns were detected 55% of the time (n = 649 years pooled across sites) with a median periodicity of 3.7 years, and non-cyclic periods were not more frequent in recent years. Overall, there was an indication for a negative effect of warm spells occurring during the snow onset period of the preceding year on lemming abundance. However, winter duration or early winter climatic conditions did not differ on average between cyclic and non-cyclic periods. Analysis of the time series shows that there is presently no Arctic-wide collapse of lemming cycles, even though cycles have been sporadic at most sites during the last decades. Although non-stationary dynamics appears a common feature of lemming populations also in the past, continued warming in early winter may decrease the frequency of periodic irruptions with negative consequences for tundra ecosystems.

Correction to: Documenting lemming population change in the Arctic: Can we detect trends?

In the original published article, some of the symbols in figure 1A were modified incorrectly during the typesetting and publication process. The correct version of the figure is provided in this correction.

Documenting lemming population change in the Arctic: Can we detect trends?

Lemmings are a key component of tundra food webs and changes in their dynamics can affect the whole ecosystem. We present a comprehensive overview of lemming monitoring and research activities, and assess recent trends in lemming abundance across the circumpolar Arctic. Since 2000, lemmings have been monitored at 49 sites of which 38 are still active. The sites were not evenly distributed with notably Russia and high Arctic Canada underrepresented. Abundance was monitored at all sites, but methods and levels of precision varied greatly. Other important attributes such as health, genetic diversity and potential drivers of population change, were often not monitored. There was no evidence that lemming populations were decreasing in general, although a negative trend was detected for low arctic populations sympatric with voles. To keep the pace of arctic change, we recommend maintaining long-term programmes while harmonizing methods, improving spatial coverage and integrating an ecosystem perspective.

The nature of lemming cycles on Wrangel: an island without small mustelids.

Lemming cycles are a key process in the functioning of tundra ecosystems. Although it is agreed that trophic interactions are important in causing the cycles, the actual mechanism is disputed. Some researchers attribute a major role to predation by small mustelids such as stoats and least weasels. Here we present a 40-year time series of lemming dynamics from Wrangel Island and show statistically that lemmings do exhibit population cycles in the absence of small mustelids. The observed density fluctuations differed, however, from those observed elsewhere, with long cycles and possibly higher densities of lemmings during the low phase. These differences in the shape of the population cycles may be related to the unique species assemblage of Wrangel Island, where arctic foxes are the only year-round resident lemming predator, and to the high diversity of landscapes, microclimatic conditions, and plants on the island. Both spectral analysis and wavelet analysis show a change in period length from five years in the 1970s to nearly eight years in the 1990s and 2000s. This change in dynamics coincides with reports of dampening or fading out of lemming cycles that have been observed in several regions of the Arctic in recent decades. As in the other cases, the changed lemming dynamics on Wrangel Island may be related to ground icing in winter, which could delay peak years.