Population Cycles Of Lemmings Research Articles

Radon as a possible link between peak spring tides and lemming cycles

There is still no consensus regarding the ultimate cause of the famous 3–4-year population cycles of lemmings. According to the plant stress hypothesis, herbivore population peaks are caused by stress factors that force plants to reallocate stored defensive proteins to transportable and easily digestible N-compounds. One possible plant stress factor is ionization caused by exhalation of the radioactive noble gas radon, which is enhanced after spring tides, i.e., tides at new or full Moon. I hypothesized that increased ionization caused by radon accumulation in the subnivean space after peak spring tides, which occur close to perihelion (31 December–05 January, when the Earth–Sun distance is shortest), and at 3.8-year intervals, results in increased protein digestibility of mosses, which are important food for lemmings. Population outbreaks of Norway lemming Lemmus lemmus occurred two years after peak spring tides during 1871–1910, when also perigee (the time when the Earth–Moon distance is shortest) coincided with spring tides and perihelion. Thereafter this relationship weakened, and lemming peaks became less pronounced and more related to plant seed indices. As we have now entered a new 30-year period with coincidence of spring tide, perihelion and perigee, I predict more regular and pronounced lemming outbreaks in the next decades, unless radon accumulation is prevented by frequent lack of a stable snow cover due to global warming.

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.

Direct and indirect effects of regional and local climatic factors on trophic interactions in the Arctic tundra

Climate change can impact ecosystems by reshaping the dynamics of resource exploitation for predators and their prey. Alterations of these pathways could be especially intense in ecosystems characterized by a simple trophic structure and rapid warming trends, such as in the Arctic. However, quantifying the multiple direct and indirect pathways through which climate change is likely to alter trophic interactions and their relative strength remains a challenge. Here, we aim to identify direct and indirect causal mechanisms driven by climate affecting predator-prey interactions of species sharing a tundra food web. We based our study on relationships between one Arctic predator (Arctic fox) and its two main prey - lemmings (preferred prey) and snow geese (alternate prey) - which are exposed to variable local and regional climatic factors across years. We used a combination of models mapping multiple causal links among key variables derived from a long-term dataset (21years). We obtained several possible scenarios linking regional climate factors (Arctic oscillations) and local temperature and precipitation to the breeding of species. Our results suggest that both regional and local climate factors have direct and indirect impacts on the breeding of foxes and geese. Local climate showed a positive causal link with goose nesting success, while both regional and local climate displayed contrasted effects on the proportion of fox breeding. We found no impact of climate on lemming abundance. We observed positive relationships between lemming, fox and goose reproduction highlighting numerical and functional responses of fox to the variability of lemming abundance. Our study measures causal links and strength of interactions in a food web, quantifying both numerical response of a predator and apparent interactions between its two main prey. These results improve our understanding of the complex effects of climate on predator-prey interactions and our capacity to anticipate food web response to ongoing climate change.

Top-down limitation of lemmings revealed by experimental reduction of predators.

It is generally recognized that delayed density-dependence is responsible for cyclic population dynamics. However, it is still uncertain whether a single factor can explain why some rodent populations fluctuate according to a 3-4yr periodicity. There is increasing evidence that predation may play a role in lemming population cycles, although this effect may vary seasonally. To address this issue, we conducted an experiment where we built a large exclosure (9ha) to protect brown lemmings (Lemmus trimucronatus) from avian and terrestrial predators. We tested the hypothesis that predation is a limiting factor for lemmings by measuring the demographic consequences of a predator reduction during the growth and peak phases of the cycle. We assessed summer (capture-mark-recapture methods) and winter (winter nest sampling) lemming demography on two grids located on Bylot Island, Nunavut, Canada from 2008 to 2015. The predator exclosure became fully effective in July 2013, allowing us to compare demography between the control and experimental grids before and during the treatment. Lemming abundance, survival and proportion of juveniles were similar between the two grids before the treatment. During the predator-reduction period, summer densities were on average 1.9× higher inside the experimental grid than the control and this effect was greatest for adult females and juveniles (densities 2.4× and 3.4× higher, respectively). Summer survival was 1.6×higher on the experimental grid than the control whereas body mass and proportion of juveniles were also slightly higher. Winter nest densities remained high inside the predator reduction grid following high summer abundance, but declined on the control grid. These results confirm that predation limits lemming population growth during the summer due to its negative impact on survival. However, it is possible that in winter, predation may interact with other factors affecting reproduction and ultimately population cycles.

Loss of periodicity in breeding success of waders links to changes in lemming cycles in Arctic ecosystems

Lemming population cycles in the Arctic have an important impact on the Arctic food web, indirectly also affecting breeding success in Arctic‐nesting birds through shared predators. Over the last two decades lemming cycles have changed in amplitude and even disappeared in parts of the Arctic. To examine the large scale effect of these recent changes we re‐analysed published data from the East Atlantic Flyway (EAF), where a relationship between lemming cycles and wader breeding success was earlier found, and new data on breeding success of waders in the East Asian–Australasian Flyway (EAAF).We found that 1) any long‐term periodicities in wader breeding success existed only until the year 2000 in the EAAF and until the 1980s in the EAF; 2) studying these patterns at a smaller spatial scale, where the Siberian–Alaskan breeding grounds were divided into five geographical units largely based on landscape features, breeding success of waders from the EAAF was not correlated to an index of predation pressure, but positively correlated to Arctic summer temperatures in some species. We argue that fading out of lemming cycles in some parts of the Arctic is responsible for faltering periodicity in wader breeding success along both flyways. These changed conditions have not yet resulted in any marked changing trends in breeding success across years, and declining numbers of waders along the EAAF are therefore more likely a result of changing conditions at stop‐over and wintering sites.

Does lemming winter grazing impact vegetation in the Canadian Arctic?

In low-productivity environments such as the tundra, it has been proposed that regular, multi-annual population cycles of lemmings could be driven by winter food depletion in years of peak abundance. If lemming population dynamics is controlled by food resources, we predict that (1) winter grazing should negatively impact the abundance of food plants, (2) this impact should be proportional to lemming density and (3) high lemming winter grazing pressure should result in reduced plant growth during the following summer. We tested these predictions on Bylot Island, Nunavut, Canada, where two species of lemmings are present: the brown (Lemmus trimucronatus) and collared lemming (Dicrostonyx groenlandicus). We installed 16 exclosures in their preferred wintering habitat (snowbeds) and annually sampled plant biomass inside and outside exclosures at snow melt and at peak growth during the summers of 2009–2012, covering a full population cycle. Winter grazing had no impact on total vascular plant or moss biomass at snow melt in all years. Among plant families, only Caryophyllaceae, which was uncommon, showed a decline. In moss taxa, a negative effect was found on Polytrichum in only 1 year out of three. Overall, plant regrowth during the subsequent summer showed annual variation and tended to be reduced in the 2 years of high lemming abundance. However, this could be a consequence of summer grazing. Overall, the impact of lemming winter grazing on plants was weak and short-lived, even in years of high lemming abundance. Therefore, our results are not consistent with the hypothesis that food depletion during winter was the cause of the lemming decline following peak abundance at our study site. Other factors may limit lemming populations and prevent them from reaching densities high enough to exhaust their food resources.

Rodent population dynamics affect seedling recruitment in alpine habitats

AbstractQuestionsHow do rodents with cyclic population dynamics affect seedling recruitment in alpine habitats? Does disturbance from rodents have larger implications on seedling recruitment in some plant communities than in others?LocationSnowbeds and sheltered heaths in the low‐alpine zone in areas of Børgefjell and Dovrefjell, Norway.MethodsWe recorded seedling emergence, rodent activity and cover of mosses, lichens, litter and bare ground in 270 plots in snowbeds and sheltered heaths in a rodent population peak year and in the following low‐density year.ResultsSeedling recruitment was positively correlated with disturbances from lemmings and voles in both years. More seedlings emerged in the low‐density year than in the year of the population peak. Snowbeds had higher seedling recruitment than the sheltered heaths, but both habitats were equally affected by disturbances from rodents.ConclusionsRodent activity created gaps and increased seedling emergence in these alpine plant communities, particularly in the year after the rodent peak, both in snowbeds and sheltered heath habitats. Our study therefore suggests that regeneration patterns in alpine vegetation are tightly linked to the population cycles of lemmings and voles, which peak in density at 3‐ to 5‐yr intervals.

The effect of snow cover on lemming population cycles in the Canadian High Arctic

Rising temperatures and changes in the precipitation regime will have a strong impact on the quality of the snow cover in the Arctic. A snow cover of good quality protecting lemmings from cold temperatures and predators is thought to be an important factor for maintaining the cyclic dynamic of their populations in the tundra. We examined if the characteristics of annual fluctuations (amplitude and shape of phases) in brown lemming (Lemmus trimucronatus) density could be determined by snow depth, snow density, sub-nivean temperature and persistence of snow. Using an 18-year time series of brown lemming abundance on Bylot Island in the Canadian Arctic, we tested if snow variables could explain the residual variation between the observed lemming density and the one predicted by models where cyclicity had been accounted for. Our analysis provides support for the hypothesis that snow cover can affect the amplitude and possibly also the periodicity of lemming population cycles in the High Arctic. Summer abundance of brown lemmings was higher following winters with a deep snow cover and a low-density snow pack near the ground but was unaffected by the date of establishment or melting and duration of the snow cover. Two snow variables showed a temporal trend; mean winter snow depth tended to increase and date of establishment of the hiemal threshold occurred earlier over time. These temporal trends, which should be favourable to lemmings, may explain why healthy population cycles have apparently been maintained at our study site contrary to other Arctic sites.

The marine side of a terrestrial carnivore: intra-population variation in use of allochthonous resources by arctic foxes.

Inter-individual variation in diet within generalist animal populations is thought to be a widespread phenomenon but its potential causes are poorly known. Inter-individual variation can be amplified by the availability and use of allochthonous resources, i.e., resources coming from spatially distinct ecosystems. Using a wild population of arctic fox as a study model, we tested hypotheses that could explain variation in both population and individual isotopic niches, used here as proxy for the trophic niche. The arctic fox is an opportunistic forager, dwelling in terrestrial and marine environments characterized by strong spatial (arctic-nesting birds) and temporal (cyclic lemmings) fluctuations in resource abundance. First, we tested the hypothesis that generalist foraging habits, in association with temporal variation in prey accessibility, should induce temporal changes in isotopic niche width and diet. Second, we investigated whether within-population variation in the isotopic niche could be explained by individual characteristics (sex and breeding status) and environmental factors (spatiotemporal variation in prey availability). We addressed these questions using isotopic analysis and Bayesian mixing models in conjunction with linear mixed-effects models. We found that: i) arctic fox populations can simultaneously undergo short-term (i.e., within a few months) reduction in both isotopic niche width and inter-individual variability in isotopic ratios, ii) individual isotopic ratios were higher and more representative of a marine-based diet for non-breeding than breeding foxes early in spring, and iii) lemming population cycles did not appear to directly influence the diet of individual foxes after taking their breeding status into account. However, lemming abundance was correlated to proportion of breeding foxes, and could thus indirectly affect the diet at the population scale.

Population cycles of lemmings near Barrow, Alaska: a historical review

Current hypotheses regarding the causes of population cycling of brown lemmingsLemmus trimucronatus (Richardson, 1828), developed during long-term studies from 1950–1974. We maintain that three factors largely determine the timing and amplitude of population cycles in brown lemmings. First, a basic interaction between lemmings and vegetation sets the stage because dense populations of lemmings severely damage the vegetation, at which point lemming populations decline and remain low until the vegetation recovers. Second, opportunistic predators, mainly jaegers and owls, assemble as the snow melts during peak years and drive already declining populations to extremely low densities. Weasels are effective predators under the snow, but they appear irregularly. If weasel populations increase early in the cycle, lemming populations that normally increase dramatically during the winter in a peak year can be decimated before the snow melts. Finally, both wet summers that result in extensive flooding of the preferred habits of lemmings and freezing rains or winter thaws that cause ice formation reduce food availability, disrupt the cycle and extend the period between peak densities. Numerous observations, experimental results and simulation models support these views. Similar results regarding the importance of the available food supply, particularly in winter, and of the predation regime also have been reported for arvicoline populations at lower latitudes.

IN MEMORIAM: FRANK ALOIS PITELKA, 1916–2003

Frank Alois Pitelka, a member of the AOU since 1937, an Elective Member since 1944, and a Fellow since 1948, died of prostate cancer on 10 October 2003. He was born in Chicago, Illinois, on 27 March 1916. He earned his B.S. at the University of Illinois (1939) and his Ph.D. from the University of California, Berkeley (1946), where he remained for his entire academic career. He retired in 1985 but continued to come regularly to the campus until 1999, when failing health forced him to join his daughter in southern California. Frank's ornithological career began in the 1930s while growing up in suburban Chicago. Although he dismissed his upbringing as distinctly non-academic, early on he joined the Chicago Ornithological Society, where he was taken under the wing of several local birders, including Nellie Johnson Baroody, in whose honor he would later endow an AOU student presentation award. During his college years, Frank published eight ornithological notes and a detailed account of the breeding biology of the Black-throated Green Warbler. After graduation, Frank spent the summer of 1939 at the University of Washington's Oceanographic Laboratories in Friday Harbor, and then moved south to the University of California at Berkeley for graduate work under Alden Miller in the Museum of Vertebrate Zoology (MVZ). A venerable MVZ tradition during that era involved staff and students making extensive field collecting trips throughout western North America and Mexico. Frank eagerly joined several of those expeditions, and for his Ph.D. investigated variation and speciation in Aphelocoma jays. Although he presumably chose that genus because of its taxonomic interest, Frank's field observations of the jays kindled an interest in the evolution of social behavior that was to form the first of two major focuses of his research career. Frank's second major research focus was population regulation. That interest developed soon after he was hired as an Instructor in Zoology and Assistant Curator of Birds in the MVZ. Gradually, his attention shifted from taxonomy to ecology, spurred along by an invitation to work at the recently established Naval Arctic Research Laboratory (NARL) in Barrow, Alaska. Thus began an annual migration between Berkeley and Barrow that Frank undertook for 30 years as he and his students studied the population cycles of lemmings and their avian predators. Later, they investigated the behavior and ecology of other Arctic-breeding birds, particularly calidridine sandpipers. A proud and unabashed naturalist, Frank belonged to that earlier generation of field biologists for whom collecting specimens, obtaining distributional data, studying life histories, and observing behavior were of paramount importance. He was especially in his element in the stark natural beauty of northern Alaska, where he enthusiastically trundled across the tundra to collect vagrants and observe the social and reproductive behavior of the avifauna. As described memorably by David W. Norton (in Fifty Years Below Zero: Tributes and Meditations for the Naval Arctic Research Laboratory's First Half-century at Barrow, Alaska, University Alaska Press, 2001), Frank became one of the station's most colorful summer residents. Frank's bibliography comprises more than 150 publications. His professional awards include the William Brewster Memorial Medal (1980) from the AOU, the Mercer (1953) and Eminent Ecologist (1992) awards from the Ecological

Relationship between El Niño /South Oscillation (ENSO) and population outbreaks of some lemmings and voles in Europe

Ecologists have been puzzled by population cycles of lemmings and voles for the over 70 years. At present, our understanding and explanation to this phenomenon remain controversial. Recently, El Nino/South Oscillation has attracted attention of ecologists on its links with population outbreaks of terrestrial animals. This paper aims to investigate the statistical relationship between outbreaks of microtine rodents and ENSO events by scanning available literature. During 1862–1894, outbreaks of Norway lemmings in Norway tended to occur in the Southern Oscillation Index (SOI) peak years or 1 year after the SOI peak years with an approximate significance level (p = 0.057). During 1885–1931, outbreaks of voles in France tended to occur 1 year before the SOI peak years (p = 0.01). During 1946–1993, outbreaks of lemmings and voles in North Finland tended to occur 1 year before the SOI peak years with a significant level (p = 0.022); the peaks of population abundance corresponded well to the SOI trough years (equal to 1 year before the SOI peak years). Outbreaks of common voles in Poland during 1946–1975 tended to occur in the SOI peak years or 1 year before the SOI peak years (p = 0.011), and also tended to occur 1 year before the SOI peak years (p = 0.030). It was also found that the rodent outbreaks in Norway and France, rodent outbreaks in Finland and Poland synchronized well. It was suggested that the ENSO-related climate or food were key factors in causing outbreaks of microtine rodents in Europe.

Grazing-Induced Proteinase Inhibitors: A Possible Cause for Lemming Population Cycles

Neutral extracts of experimentally wounded Carex bigelowii and Eriophorum angustifolium inhibit the proteolytic activity of trypsin. Increasing trypsin inhibitor activity was associated with a concomitant decrease in the concentration of soluble plant proteins (TI/SPP-ratio). At different phases of a three year lemming cycle, the TI/SPP-ratio was highest at peaking and declining densities and lowest when lemming density increased. Moreover, lemmings from a declining population showed pancreatic hypertrophy, which is a well documented pathology caused by a prolonged dietary intake of trypsin inhibitors

Changing Reproductive Rates and Population Cycles in Lemmings and Voles

Changing Reproductive Rates and Population Cycles in Lemmings and Voles

Efficiency of Winter Scavengers in the Arctic

Frozen carcasses of brown lemmings, Lemmus trimucronatus , were systematically placed under the snow in various tundra habitats in the fall of 1961 (188), 1962 (201) and 1963 (205) near Barrow, Alaska. Only 8 carcasses were recovered in the following springs. Removal of the carcasses is attributed to: arctic fox ( Alopex lagopus) and red fox ( Vulpes fulva ); brown lemming; the least weasel ( Mustela rixosa ). Observations of behaviour, systematic trapping and examination of scats were used to suggest the relative importance of these consumers of lemming carrion in the order given above. The inability of investigators of lemming population cycles to find the carcasses of lemmings that die during the winter months is explained by the unusual efficiency of these species in locating and using frozen carrion during the winter months.