Height of an adult lemming-Norway lemming - Wikipedia

Use the link below to share a full-text version of this article with your friends and colleagues. Learn more. The causes of cyclical fluctuations in animal populations remain a controversial topic in ecology. Food limitation and predation are two leading hypotheses to explain small mammal population dynamics in northern environments. We documented the seasonal timing of the decline phases and demographic parameters survival and reproduction associated with population changes in lemmings, allowing us to evaluate some predictions from these two hypotheses.

Height of an adult lemming

The wet habitat consists primarily of a mosaic of tundra polygons, ponds and thaw lakes and is common in the valley bottom. Summary The causes of cyclical fluctuations in animal populations remain a controversial topic in ecology. Our study presents for the first time a detailed analysis of the seasonal summer and winter demography of a lemming species over multiple cycles. Balkan snow vole D. This animal. Lemmings are herbivores with a main diet of moss and grass. In rocky areas, a cod Height of an adult lemming be a darker brown colour. Returning user.

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Lemmings do not hibernate and instead endure the tough Arctic winters, with the lemming having special protection from the cold from its thick fur.

  • Lemmings do not hibernate and instead endure the tough Arctic winters, with the lemming having special protection from the cold from its thick fur.
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  • A lemming is a small rodent , usually found in or near the Arctic in tundra biomes.
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Use the link below to share a full-text version of this article with your friends and colleagues. Learn more. The causes of cyclical fluctuations in animal populations remain a controversial topic in ecology. Food limitation and predation are two leading hypotheses to explain small mammal population dynamics in northern environments. We documented the seasonal timing of the decline phases and demographic parameters survival and reproduction associated with population changes in lemmings, allowing us to evaluate some predictions from these two hypotheses.

We also examined the effects of some weather variables on survival. We found that population declines after a peak occurred between the summer and winter period and not during the winter. During the summer, population growth was driven by change in survival, but not in fecundity or proportion of juveniles, whereas in winter population growth was driven by changes in late summer and winter reproduction. We did not find evidence for direct density dependence on summer demographic parameters, though our analysis was constrained by the paucity of data during the low phase.

Body mass, however, was highest in peak years. Weather effects were detected only in early summer when lemming survival was positively related to snow depth at the onset of melt but negatively related to rainfall.

Our results show that high mortality causes population declines of lemmings during summer and fall, which suggests that predation is sufficient to cause population crashes, whereas high winter fecundity is the primary factor leading to population irruptions.

The positive association between snow depth and early summer survival may be due to the protective cover offered by snow against predators. It is still unclear why reproduction remains low during the low phase.

Yet, such information is crucial to fully understand factors driving the dynamics of these populations Krebs According to the first hypothesis, population cycles should be controlled by variations in food abundance or quality due to a delayed response of plants to grazing.

Alternatively, overgrazing of plants during population peaks may cause the decline of small mammal populations, and low food abundance may limit subsequent population growth as plants need time to recover. One important difference exists between the predation and food abundance hypotheses as applied to the control of small tundra herbivores, namely the period of the year when conditions should be most limiting.

Determining the seasonal timing of each phase of lemming population cycles i. However, few studies have analysed variations in lemming survival in relation to climatic factors.

Thus, a combination of long time series of summer and winter demographic data can be used to pinpoint more accurately when population increases and declines occur, and determine which demographic factors are associated with seasonal population changes.

We had three objectives. First, we studied the seasonal timing of lemming population changes over three population cycles to determine whether declines occurred between the winter and early summer as predicted by the food abundance hypothesis or between summer and winter as predicted by the predation hypothesis.

Our second objective was to identify changes in demographic parameters that are recurrent and associated with population fluctuations. We examined whether summer population growth was mostly related to change in survival, fecundity or proportion of juveniles and whether winter growth was related to fecundity and proportion of juveniles. Our third objective was to study the effects of selected weather variables on summer survival of lemmings.

In contrast, we hypothesized that heavy summer rainfall should reduce summer survival, especially during spring thaw.

The wet habitat consists primarily of a mosaic of tundra polygons, ponds and thaw lakes and is common in the valley bottom. The surrounding slopes and hills as well as higher grounds in the valley are characterized by mesic tundra, the dominant habitat.

The vegetation of the wet habitat is composed of sedges Eriophorum spp. Only two rodent species are present on Bylot Island: brown and collared lemmings. Other herbivores include the snow goose Anser caerulescens ; during the summer only and arctic hare Lepus arcticus and rock ptarmigan Lagopus muta at very low densities. We thus used data from this grid to estimate summer demographic parameters, but not winter parameters. We activated one grid at a time and trapping was done consecutively on the three grids at each primary occasion.

Females were noted as lactating or gravid when their mammary glands were visible or when foetuses were palpable. From to , males were noted as reproductive if their scrotum was visible.

All subsequent recaptures were noted. We estimated five demographic parameters during the summer: population density D , survival S , fecundity B , proportion of juveniles J and body mass M. Three separate estimates of each parameter were calculated for lemmings trapped on each grid in June, July and August, except for survival which was calculated for the two intervals. From to , lemmings trapped during both periods of July were pooled as one July group for B , J and M estimations.

Sample sizes are provided in Appendix S1 Supporting Information. We estimated the fecundity of females as the proportion of adult females that were lactating or gravid, and the proportion of juveniles among all captured individuals.

Starting in , we sampled winter nests after snow melt. While walking along each transect, we removed all winter nests found and recorded the perpendicular distance from the transect. Nests are easy to detect at our site due to the low vegetation height. We eliminated from the analysis the small number of nests containing faeces of both species.

We used the line transect method Buckland and the software distance 6. We collected snow and rainfall data at the study site every year. Spring snow depth was monitored annually from ca 25 May to 3 June until disappearance around 20 June. The transects encompassed the two main habitats, wet and mesic. We used the average snow depth observed between 5 and 7 June to obtain an annual measure in spring because these dates were available through all years of the study.

We averaged daily rainfall for two periods: early 6 June—20 July and late summer 21 July—20 August. Trapping grids were used as a random factor because the same grids were sampled repeatedly.

We used two time units to study changes in population density: intraseasonal between months, m for summer analyses and interannual w for winter analyses. We used separate models because several of these independent variables were highly correlated see 3.

We further assessed the relationship between annual change in winter nest density and population density measured in August model M5. In simple linear regressions between two variables measured with an error, such as survival and population density, the uncertainty associated with the slope should consider variance components of both variables. Coefficients estimated with ranged major axis regressions assume that the response and explanatory variables are correlated, which was verified.

We tested for direct density dependence on summer survival, proportion of juveniles, adult body mass both sexes combined and fecundity i. Post hoc multiple comparisons were conducted using Tukey's tests to determine whether there were differences between months. We used LMMs to assess potential effects of weather variables on demographic parameters, also using trapping grid as a random variable. We examined the relationships between June—July survival dependent variable and spring snow depth or June—July rainfall, and between July—August survival and July—August rainfall.

Brown lemmings showed large fluctuations in abundance Fig. During summer , population density was high but declined to reach very low values in early summer until summer Nest density increased in winter — compared to the previous one.

Population density was high in early summer but winter nest density indicated that it had declined to low levels by the following winter and remained low in summer Nest density increased in winter — as well as population density in summer compared to the previous year. Nest and population densities remained high during winter — and early summer Population density declined in summer , and nest density was very low during the following winter. Lemming abundance was very low during summers and and the winter in between.

Sample size allowed an estimation of summer survival only in years of high abundance , , and The most parsimonious models for estimating probabilities of survival differed between years see Appendix S2 for model selection. In and , models with constant survival between months and trapping grids were preferred, but survival probabilities differed between trapping grids in and trapping grids and months in Estimation of summer fecundity was also possible only in years of high abundance.

The proportion of juveniles could be estimated in most years except in and a few periods in , and The average body mass of adult lemmings could not be estimated in , and some periods in , and Thus, when density of winter nests and reproductive rates were high, the population increased, but it decreased when these parameters were low Fig.

Similarly, population growth rate over winter was positively related to the proportion of reproductive females in August M3, Fig. In contrast, annual change in winter nest density was negatively related with population density in late August M5. During the summer, monthly growth rate of lemming populations was positively related to their survival rate M6, Fig. Our results show that lemming population declines occurred between the late summer and winter periods on Bylot Island.

Indeed, a large population decline between late summer and the following spring was associated with a very low abundance of winter nests and was further confirmed by the negative relationship between annual change in winter nests and late summer density. Our results show that reproductive activity in those nests can be very high in some years. However, these features are absent from most of the Canadian High Arctic due to the sparse vegetation cover.

Therefore, as the ground freezes in the fall and snow sets in, these nests become important shelters. The strong positive relationship between winter population growth rate and reproductive activity substantiates previous suggestions that lemming population growth is conditional to high winter reproduction Millar ; Krebs The seasonal pattern in brown lemming population changes that we document here differs from the one reported in northern Alaska.

Recent evidence shows that, unlike what has been reported for Lemmus elsewhere, brown lemmings on Bylot Island consume willows Salix spp. Thus, a lack of food during winter, as predicted by the food abundance hypothesis, is unlikely to explain the periodic declines of brown lemmings in the Canadian Arctic. We found a highly interesting contrast between summer and winter in the demographic factors associated with lemming population changes.

During the summer, population growth was apparently driven by change in survival, but not in fecundity or proportion of juveniles, whereas in winter it was driven by changes in late summer and winter reproduction. Even though we used capture—recapture methods to estimate survival, we recognize that mortality is here confounded with permanent emigration, which includes dispersal, and could vary with phases of the cycle.

However, given that survival could only be estimated in years of moderately high abundance, variations in dispersal rate with cycle phase should not be a serious issue here. Although we could not measure survival probability during winter, the contrasting effects of fecundity on summer and winter population growth rates indicate that factors limiting lemmings vary seasonally.

Young born in winter will have matured and should be able to reproduce during the summer, which could explain why the proportion of juveniles in the population peaked in late summer. Nonetheless, high reproductive activity did not prevent the summer population to decline. Thus, lemming survival should improve as soon as the snow cover settles, which may explain why fecundity then becomes a driver of lemming population change, unlike in the summer.

Interestingly, winter population growth rate was also positively associated with fecundity in August. We did not find any evidence for direct density dependence on summer demographic parameters, which indicates that density had little direct effect on summer growth.

Lophiomyinae 1 animal. Kintampo rope squirrel. Northern hopping mouse. Eurasian water shrew. Figure 1: The collared lemming, Dicrostonyx torquatus, is one of three lemming species found in Canada's Arctic. Gambian epauletted fruit bat.

Height of an adult lemming

Height of an adult lemming. Lemming Location

The lemmings spend the winter searching for bulbs and shoots that are often buried beneath the snow. Lemmings are surprisingly solitary animals , only coming together to mate then separating again. Wild lemmings are thought to never get older than a couple of years due the harsh conditions in their natural habitat and the small and very edible size of the lemming.

The lemming is easy prey for most meat-eating mammals and birds. The theory that older lemmings consciously jump off cliffs in large numbers in order to let the younger lemming generations have full access to food and shelter etc is a myth. This may have originated from the mass migration of the Scandinavian lemming when food becomes scarce, that run in their hundreds through the surrounding terrain in search of food, with a few unlucky individuals finding their way off cliffs.

There are nearly 30 different species of lemming found around the Arctic Circle, from Alaska to Siberia. Although many different species of lemming have been recognised, all lemming species are pretty much the same apart from where they live and so the lemming species tend to differ most from one another based on what the lemmings can find to eat. Lemmings have small, stout bodies and short limbs, ears and tail in order to allow the lemming to conserve heat more easily in the bitter Arctic winters.

Lemmings also have sharp little teeth which helps the lemmings to gnaw through tangles of roots. Female lemmings give birth to the baby lemmings after a gestation period of around three weeks. Baby lemmings are born in burrows under the snow which helps to keep the baby lemmings warm and away from the Arctic winter. The mother lemming gives birth to around 7 baby lemmings and feeds the baby lemmings on her milk until they are big enough and strong enough to start looking for food by themselves.

The food that lemmings eat is not very nutritious, so lemmings must eat lots of it. Lemmings spend around 6 hours a day searching for food and have breaks in between hunting, during which the lemmings rest. Lemmings reside in burrows beneath the snow to keep them warm and safe from predators that lurk on the surface of the snow. View all animals that start with L. Are you Safe? If something has upset you, the Are you Safe? Lemming Location. Share This Article. Related Animals Arctic Hare Eats berries found in the snow!

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This animal. Lemmings are mouselike rodents that live in treeless areas of northern Canada. They have short ears, largely hidden in the fur, short legs, and short tails. Their fur is a full brown and grey summer and winter. In summer, a collared lemming has a black nose, grey cheeks, tawny ear spots, a chestnut collar, and a more or less prominent black dorsal stripe.

With the autumn moult, however, the summer coat is replaced by a solid white winter one and the front feet develop two greatly enlarged claws, presumably to help dig through the hard-packed tundra snow. Unique characteristics Lemming populations have long been known to fluctuate drastically. Peak numbers tend to recur about every four years. Furthermore, numbers are high over a huge area: for example, was a "lemming year" for almost all of the Canadian Arctic.

All sorts of reasons for the cycles have been suggested, from changes in the number of sunspots to snow conditions. Weather is a likely, but still unproven, trigger. Winter creates problems for lemmings, the amount and timing and distribution of snow mitigate those problems, and peak numbers occur only following winter breeding.

Unfortunately, no one has yet studied the role of snow cover in sufficient detail to prove that it causes the cycle. A remarkable feature of the lemming cycle is the extreme scarcity of individuals at the "low point" of the cycle. Although several species of small rodents that live in temperate climates also reach peaks of abundance about every four years and some of them reach much higher densities at the peak than lemmings do, none can equal the extreme scarcity of lemmings at the low point.

Such extreme scarcity raises the possibility of extinction. But passing through a population "bottleneck" probably strongly favours the individuals best adapted to survival in harsh arctic conditions.

The cycle of every four years or so may be a device to keep selection abreast of the changes continually going on in the Arctic. An early theory was that regular cycles of scarcity and abundance resulted from the interaction between a predator and its prey.

When the prey became numerous, the predators brought down their numbers, which then resulted in death by starvation for the predator. However, the shoe now seems to be on the other foot.

We know that nesting success of Snowy Owls and survival of arctic fox pups are both related to lemming abundance. Both owls and foxes produce very few, if any, surviving young except in "lemming years. Another theory was the obvious one of epidemic disease periodically sweeping through the lemming population. The larger the population and the more contact between individuals in overcrowded conditions, the easier the spread of an infection. Unfortunately, no one has found a disease that is rampant in all declining lemming populations.

During some declines disease is virtually absent. Another obvious candidate is the interaction between lemmings and their food supply.

As lemming numbers increase so does damage to the vegetation. Ultimately, the food supply is no longer able to sustain the population. Following a die-off of lemmings, the vegetation is able to recover, which sets the stage for a new cycle. The quantity and quality of available food are known to vary with the stage of the lemming cycle, but proof of cause and effect is still lacking. In recent years, researchers have focused on changes in the animals themselves. The first measurable evidence came from noting changes in average weights of individuals in different phases of the cycle.

In a number of species of small mammals, the largest individuals are found in the spring of the peak year. Researchers are now looking for more subtle changes. For example, increasing density produces more social interaction between individuals, which induces stress, which results in altered hormone levels, which may interfere with reproduction or alter behaviour.

Stress itself may lead to increased mortality. Lemmings tend to be aggressive toward one another. If the behavioural alteration were in the direction of an increase in aggression, fewer lemmings would be born and more would be killed by their own kind.

In Scandinavia, lemmings become restless when their populations are high. In the mountainous terrain of Norway, for example, when lemmings begin to move they tend to go downhill and get funneled into valleys. The result is that large numbers eventually reach the sea or a large lake. They may proceed onto sea or lake ice or jump into the water, which has given rise to the popular conception that they are committing mass suicide to relieve a problem of overpopulation. There is, however, no authentic account from the North American Arctic to back up such a belief.

Most of our Canadian lemmings live on rather flat terrain and too far from the ocean to make such migrations possible.

The Inuit have no legends about migrating lemmings and it is difficult to believe that they would have overlooked such an event, especially if it occurred repeatedly. It is certainly true that in the spring of a high population year individual lemmings will often be seen on lake and sea ice, but they do not move in an orientated manner, all going north or all going south like migrating birds, and large groups are never seen.

Once on the ice, individuals run rapidly and tend to move in straight lines. Lemmings have been seen on sea ice as far as 55 km from the nearest land. We do not understand why lemmings would move onto sea and lake ice in the spring of peak years, but spring is a time of social upheaval caused by the environmental changes associated with snow melt, and the physiological changes associated with onset of the breeding season.

The smallest of the mammals of the High Arctic, lemmings are key species in arctic ecosystems. For unknown reasons, lemming populations fluctuate drastically, peaking about every four years and then crashing almost to extinction.

Because the small bodies of lemmings are important food for ermines, arctic foxes, Snowy Owls, Gyrfalcons, and jaegers, this mysterious cycle controls the rhythm of animal life on the tundra. Most of the range occupied by lemmings is underlain by permafrost, or soil that is always frozen, often within a few centimetres of the surface. This means that the lemmings are unable to dig deep burrows for shelter even in summer. Where the soil contains much water, however, seasonal freezing and thawing creates ridges and depressions that lemmings use for burrows and as travel routes, respectively.

Brown and collared lemmings in the same general area tend to choose different habitats in summer. Collared lemmings use higher and drier sites, and brown lemmings the lower and wetter ones. This segregation coincides with the distributions of preferred forage; for example, depending on what is available, collared lemmings might seek out willows and cranberries, and brown lemmings prefer sedges, arctic cotton, and certain mosses.

In winter, the habitat segregation tends to break down as collared lemmings move to lower ground where the snow is deeper and provides more shelter.

The long arctic winter is a critical time for lemmings because, unlike many species of temperate rodents, they do not hibernate. It is amazing that these small, warm-blooded animals remain active throughout the arctic winter without freezing to death. Their short appendages ears, legs, tails are an adaptation to reduce heat loss, and their winter fur is thicker than that of summer.

As winter approaches, lemmings make large, globular nests of finely shredded grasses and sedges on the surface of the ground, which provide additional insulation when they are not out hunting for food. Snow provides critical insulation. Lemmings forage in the space that forms between soil and snow, known as subnivean space, almost never appearing on the surface. There are three lemming species in the Canadian Arctic. Two species occur on the mainland tundra west of Hudson Bay and in the southern part of the arctic archipelago: the brown lemming Lemmus sibiricus , whose range extends southwards in mountainous areas see map , and the collared or varying lemming Dicrostonyx torquatus , which has colonized the Queen Elizabeth Islands right to the northern tip of Ellesmere Island.

The collared or varying lemmings that inhabit the Ungava Peninsula are usually considered to be a separate species Dicrostonyx hudsonius. Similar lemming species are found in other circumpolar countries, such as Norway, Greenland, and Russia. In taxonomy, or the science of classifying organisms, brown and varying lemmings are classified as microtines, along with the muskrats, bog lemmings, and voles of southern Canada.

Lemmings of both sexes are able to reproduce within weeks of their birth. The proportion that reproduces in the summer of their birth varies widely from year to year, and seems to be related to population density. After a year, a female is capable of producing three litters of young even in the short arctic summer, but most fail to do so. The length of the summer breeding season is related to population density.

When numbers are low, breeding continues into September; when numbers are high, breeding may end in July. Lemmings sometimes breed in the winter, but there is always a pause in spring and fall separating summer and winter breeding.

How such a small mammal, already under a severe thermal stress, can muster enough energy to breed in an arctic winter, and what factors determine when winter breeding will occur, are still mysteries. Although lemmings have lived for up to three years in captivity, probably no lemming survives more than one winter in the wild. Wild predators likely kill most of them except perhaps during major die-offs, when other factors, such as starvation, may come into play.

In the snow-free season, arctic foxes, ermines, Snowy Owls, jaegers, and Gyrfalcons all take their toll. Wolves may take the occasional individual, and even caribou and fish have been known to prey on lemmings. Although life is more secure under the winter snow, several investigators who were on the tundra when the snow was melting have discovered remains of lemming nests that showed signs of ermine predation. The ermine is completely at home under the snow. Even higher rates of predation by ermines have been recorded on Banks Island in the Northwest Territories and in Alaska.

Snowy Owls, the only raptors, or birds of prey, present in winter, are poorly equipped for digging through snow, so an owl could only strike a lemming on the snow surface. The small arctic fox can dig through the wind-packed tundra snow, but the energy cost is high for such a small meal. In general, lemmings are not threatened by human activity except locally around villages, mines, oil wells, and other industrial sites.

Adverse weather conditions probably kill a fair number. In fall, early onset of low temperatures in the absence of snow is potentially lethal. And in spring, during snow melt, when the insulating quality of snow declines, lemmings can find themselves at the mercy of the elements if the weather turns nasty. Winter nests may be full of water, and summer burrows plugged with ice due to refreezing of the melting snow.

Although lemmings are known to suffer from a number of infectious diseases and to harbour a variety of parasites, relatively few lemmings die of diseases or parasites. Inuit do not eat lemmings, nor do they make any use of their small skins. However, those Inuit who support themselves in whole or in part by trapping benefit indirectly from the "run" of arctic foxes that follows each lemming peak. One of the Inuit names for the collared lemming is kilangmiutak, which means "one-who-comes-from-the-sky.

It probably arose because of the sudden appearance of lemmings when the snow melts following a winter of intensive reproduction. Lemmings, particularly the collared lemming with its presumed origin from the sky, were sometimes used by shamans as a source of supernatural powers.

Height of an adult lemming