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.

Flexibility in a changing arctic food web: Can rough-legged buzzards cope with changing small rodent communities?

Indirect effects of climate change are often mediated by trophic interactions and consequences for individual species depend on how they are tied into the local food web. Here we show how the response of demographic rates of an arctic bird of prey to fluctuations in small rodent abundance changed when small rodent community composition and dynamics changed, possibly under the effect of climate warming. We observed the breeding biology of rough-legged buzzards (Buteo lagopus) at the Erkuta Tundra Monitoring Site in southern Yamal, low arctic Russia, for 19 years (1999-2017). At the same time, data on small rodent abundance were collected and information on buzzard diet was obtained from pellet dissection. The small rodent community experienced a shift from high-amplitude cycles to dampened fluctuations paralleled with a change in species composition toward less lemmings and more voles. Buzzards clearly preferred lemmings as prey. Breeding density of buzzards was positively related to small rodent abundance, but the shift in small rodent community lead to lower numbers relative to small rodent abundance. At the same time, after the change in small rodent community, the average number of fledglings was higher relative to small rodent abundance than earlier. These results suggest that the buzzard population adapted to a certain degree to the changes in the major resource, although at the same time density declined. The documented flexibility in the short-term response of demographic rates to changes in structure and dynamics of key food web components make it difficult to predict how complex food webs will be transformed in a warmer Arctic. The degree of plasticity of functional responses is indeed likely to vary between species and between regions, depending also on the local food web context.

Vole abundance and reindeer carcasses determine breeding activity of Arctic foxes in low Arctic Yamal, Russia.

BACKGROUND: High latitude ecosystems are at present changing rapidly under the influence of climate warming, and specialized Arctic species at the southern margin of the Arctic may be particularly affected. The Arctic fox (Vulpes lagopus), a small mammalian predator endemic to northern tundra areas, is able to exploit different resources in the context of varying tundra ecosystems. Although generally widespread, it is critically endangered in subarctic Fennoscandia, where a fading out of the characteristic lemming cycles and competition with abundant red foxes have been identified as main threats. We studied an Arctic fox population at the Erkuta Tundra Monitoring site in low Arctic Yamal (Russia) during 10 years in order to determine which resources support the breeding activity in this population. In the study area, lemmings have been rare during the last 15 years and red foxes are nearly absent, creating an interesting contrast to the situation in Fennoscandia. RESULTS: Arctic fox was breeding in nine of the 10 years of the study. The number of active dens was on average 2.6 (range 0-6) per 100 km2 and increased with small rodent abundance. It was also higher after winters with many reindeer carcasses, which occurred when mortality was unusually high due to icy pastures following rain-on-snow events. Average litter size was 5.2 (SD = 2.1). Scat dissection suggested that small rodents (mostly Microtus spp.) were the most important prey category. Prey remains observed at dens show that birds, notably waterfowl, were also an important resource in summer. CONCLUSIONS: The Arctic fox in southern Yamal, which is part of a species-rich low Arctic food web, seems at present able to cope with a state shift of the small rodent community from high amplitude cyclicity with lemming dominated peaks, to a vole community with low amplitude fluctuations. The estimated breeding parameters characterized the population as intermediate between the lemming fox and the coastal fox ecotype. Only continued ecosystem-based monitoring will reveal their fate in a changing tundra ecosystem.

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.

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.