Dicrostonyx Groenlandicus Research Articles

Evaluation of a method to determine the breeding activity of lemmings in their winter nests

Winter breeding under the snow is a critical ecological adaptation of lemmings and a key demographic process in their periodic multiannual fluctuations in abundance. However, logistic constraints limit our ability to quantify lemming winter reproduction. We evaluated a method to infer lemming reproduction based on the size distribution of feces found in their winter nests. We determined criteria allowing identification of reproduction from feces found in nests, using golden Syrian hamsters (Mesocricetus auratus) as a surrogate model. We found a large difference in individual mass of feces between juveniles at weaning and adults. Using bimodal distribution of feces size, mean size difference, and proportion of small feces, we showed that visual inspection of ≥30 feces was sufficient to infer hamster reproduction with an accuracy of >95%. We also applied the method to winter nests of collared lemmings (Dicrostonyx groenlandicus) and brown lemmings (Lemmus trimucronatus) found in the Canadian Arctic. Because characteristics of feces found in lemming winter nests matched those found in hamster nests, we suggest that the method can be used to detect winter reproductive activity of lemmings.

Fluctuations in lemming populations in north Yukon, Canada, 2007–2010

We estimated population density of brown lemmings ( Lemmus sibiricus (Kerr, 1792)), Greenland collared lemmings ( Dicrostonyx groenlandicus (Traill, 1823)), and tundra voles ( Microtus oeconomus (Pallas, 1776)) on Herschel Island from 2007 to 2010 by mark–recapture on three live-trapping areas. Limited data were also available from Komakuk Beach on the north Yukon coast. In contrast to most previous studies, brown and collared lemmings were partly out of phase. Brown lemmings on Herschel reached peak density in 2007–2008 and were low in 2009–2010, while collared lemmings were at peak density in 2007–2008 and again in 2010. Large adult male body size was characteristic of peak populations. Brown lemmings increased dramatically in the peak summer of 2008 and collared lemmings increased rapidly when winter breeding under the snow was successful in 2009–2010. By contrast, at Komakuk Beach, we could see no clear signs of fluctuations in these three species. Winter snow conditions may be too severe for population persistence on the coastal plain along the north coast of the Yukon. Further work is needed to unravel why peak lemming densities are so variable among sites and why lemming fluctuations are so pronounced on the arctic coastal plain of Alaska and virtually absent on the coastal plain of the north Yukon.

Forecasting ecological and evolutionary strategies to global change: an example from habitat selection by lemmings

Ecologists and evolutionary biologists must develop theories that can predict the consequences of global warming and other impacts on Earth's biota. Theories of adaptive habitat selection are particularly promising because they link distribution and density with fitness. The evolutionarily stable strategy that emerges from adaptive habitat choice is given by the system's habitat isodar, the graph of densities in pairs of habitats such that the expectation of fitness is the same in each. We illustrate how isodars can be converted into adaptive landscapes of habitat selection that display the density- and frequency-dependent fitness of competing strategies of habitat use. The adaptive landscape varies with the abundance of habitats and can thus be used to predict future adaptive distributions of individuals under competing scenarios of habitat change. Application of the theory to three species of Arctic rodents living on Herschel Island in the Beaufort Sea predicts changes in selection gradients as xeric upland increases in frequency with global warming. Selection gradients will become more shallow for brown lemming (Lemmus trimucronatus) and tundra vole (Microtus oeconomus) strategies that preferentially exploit mesic habitat. Climate change will cause selection gradients for the alternative strategy of using mostly xeric habitat to become much steeper. Meanwhile, the adaptive landscape for collared lemmings (Dicrostonyx groenlandicus), which specialize on xeric Dryas-covered upland, will become increasingly convex. Changes in the adaptive landscapes thus predict expanding niches for Lemmus and Microtus, and a narrower niche for Dicrostonyx. The ability to draw adaptive landscapes from current patterns of distribution represents one of the few methods available to forecast the consequences of climate change on the future distribution and evolution of affected species.

Breeding Arctic Terns Kill Lemmings

Arctic terns (Sterna paradisaea) are well known for exhibiting vigorous defense of nests at their breeding colonies. However, in 2008 we observed a previously unreported behavior by terns. We watched chick-rearing adult terns attacking collared lemmings (Dicrostonyx groenlandicus), which included repeatedly lifting them into the air and dropping them to the tundra until they died. Terns attack certain birds and mammals that intrude on their breeding territory but do not attack other species that are known to depredate eggs, suggesting that the ability of terns to discriminate threats is imperfect.

Demography of two lemming species on Bylot Island, Nunavut, Canada

Lemmings play a key role in the tundra food web and their widely reported cyclic oscillations in abundance may have a strong effect on other components of the ecosystem. We documented seasonal and annual variations in population density, reproductive activity, survival, and body mass of two sympatric species, the brown (Lemmus trimucronatus) and collared lemmings (Dicrostonyx groenlandicus), over a 2-year period on Bylot Island, Nunavut, Canada. We live trapped and marked lemmings on two grids throughout the summer and we estimated demographic parameters using three different capture–recapture methods. All three methods are based on robust estimators and they yielded similar population density estimates. The density of brown lemmings declined markedly between the 2 years whereas that of collared lemmings was relatively constant. For brown lemmings, 2004 was a peak year in their cycle and 2005 a decline phase. Density of brown lemmings also decreased during the summer, but not that of collared lemmings. The recruitment of juvenile brown lemmings in the population increased during the summer and was higher in the peak year than in the year after, but no change was detected in collared lemmings. Survival rates of both species tended to be lower during the peak year than in the following year and body mass of brown lemmings was higher in the peak year than in the following year. We conclude that both changes in adult survival and juvenile recruitment occur during the population decline of brown lemmings.

Cyclic dynamics of sympatric lemming populations on Bylot Island, Nunavut, Canada

We characterized the fluctuations (amplitude, periodicity) of two sympatric species, the brown lemming ( Lemmus sibiricus (Kerr, 1792)) and the northern collared lemming ( Dicrostonyx groenlandicus (Traill, 1823)), in a High Arctic area. Our objective was to determine if these populations were cyclic, and if fluctuations in numbers were synchronized between the two species temporally and spatially. An annual index of lemming abundance was obtained using snap-traps at two sites 30 km apart on Bylot Island (Nunavut, Canada) over 13 years (1993–2005) and 9 years (1997–2005), respectively. The time series were analyzed by spectral analyses and autoregressive modelling. At the site with the longest record, brown lemming showed regular population fluctuations of large amplitude (>40-fold), but collared lemming fluctuations were of much smaller amplitude (4-fold). At the other site, the collared lemming population was higher than at the main site, but brown lemmings were still most abundant in the peak year. Models with a second-order function obtained from a spectral analysis were highly correlated with the observed abundance index in both species at the site with the longest time series, and provide evidence of cyclic dynamic. The periods of the cycles were estimated at 3.69 ± 0.04 (SE) years for brown lemmings and 3.92 ± 0.24 (SE) years for collared lemmings, but the amplitude of the cycle was weak in the latter species. Fluctuations in abundance at the same site were relatively well synchronized between the two species, but the evidence for synchrony between sites was equivocal.

Prolonging the arctic pulse: long‐term exploitation of cached eggs by arctic foxes when lemmings are scarce

1. Many ecosystems are characterized by pulses of dramatically higher than normal levels of foods (pulsed resources) to which animals often respond by caching foods for future use. However, the extent to which animals use cached foods and how this varies in relation to fluctuations in other foods is poorly understood in most animals. 2. Arctic foxes Alopex lagopus (L.) cache thousands of eggs annually at large goose colonies where eggs are often superabundant during the nesting period by geese. We estimated the contribution of cached eggs to arctic fox diets in spring and autumn, when geese were not present in the study area, by comparing stable isotope ratios (delta(13)C and delta(15)N) of fox tissues with those of their foods using a multisource mixing model in Program IsoSource. 3. The contribution of cached eggs to arctic fox diets was inversely related to collared lemming Dicrostonyx groenlandicus (Traill) abundance; the contribution of cached eggs to overall fox diets increased from < 28% in years when collared lemmings were abundant to 30-74% in years when collared lemmings were scarce. 4. Further, arctic foxes used cached eggs well into the following spring (almost 1 year after eggs were acquired) - a pattern that differs from that of carnivores generally storing foods for only a few days before consumption. 5. This study showed that long-term use of eggs that were cached when geese were superabundant at the colony in summer varied with fluctuations in collared lemming abundance (a key component in arctic fox diets throughout most of their range) and suggests that cached eggs functioned as a buffer when collared lemmings were scarce.

Animal models of obesity

Background Obesity stems from a prolonged imbalance between the levels of energy intake and expenditure, with the resultant surplus being stored as body lipids. Our understanding of the regulation of food intake and the physiological basis of differences in energy expenditure is owed, in large part, to studies made on animals. Moreover, animal models have been a cornerstone of studies of environmental effects, such as epigenetics, responses to high-fat and low-calorie diets and the identification and development of pharmaceuticals for obesity treatment. This review provides some examples of the animal work that has been performed, and focuses on the variation in approaches that have been taken and their potential, rather than aiming to be a comprehensive summary.

Photoperiod alters affective responses in collared lemmings

This study examined photoperiodic regulation of affective behaviours in collared lemmings ( Dicrostonyx groenlandicus). Male and female lemmings were housed in either long (LD 22:2), intermediate (LD 16:8), or short days (LD 8:16) for 9 weeks. Exposure to short days induced moult to a winter pelage and gonadal regression in male, but not female, lemmings. Lemmings housed in long days reduced anxiety-like responses in the elevated plus maze. Depressive-like behaviours were decreased in the intermediate photoperiod relative to other photoperiod groups.

Photoperiod Differentially Affects Immune Function and Reproduction in Collared Lemmings (Dicrostonyx groenlandicus)

Many nontropical rodent species experience predictable annual variation in resource availability and environmental conditions. Individuals of many animal species engage in energetically expensive processes such as breeding during the spring and summer but bias investment toward processes that promote survival such as immune function during the winter. Generally, the suite of responses associated with the changing seasons can be induced by manipulating day length (photoperiod). Collared lemmings (Dicrostonyx groenlandicus) are arvicoline rodents that inhabit parts of northern Canada and Greenland. Despite the extreme conditions of winter in their native habitat, these lemmings routinely breed during the winter. In the laboratory, collared lemmings have divergent responses to photoperiod relative to other seasonally breeding rodents; short day lengths can stimulate, rather than inhibit, the reproductive system. Male and female collared lemmings were maintained for 11 weeks in 1 of 3 photoperiods (LD 22:2, LD 16:8, or LD 8:16) that induce markedly different phenotypes. Following photoperiod treatment, cell-mediated immune function as assessed by delayed-type hypersensitivity reactions was elevated in lemmings housed in LD 16:8 and LD 8:16 relative to LD 22:2. However, antibody production to a novel antigen was unaffected by photoperiod. Exposure to LD 8:16 induced weight gain, molt to a winter pelage, and in contrast to previous studies, regression of the male, but not the female, reproductive tract. In conclusion, these data indicate that components of immune function among collared lemmings are responsive to changes in day length.

Functional and numerical responses of four lemming predators in high arctic Greenland

The high‐arctic tundra ecosystem has the world's simplest vertebrate predator–prey community, with only four predators preying upon one rodent species, the collared lemming (Dicrostonyx groenlandicus). We document the functional and numerical responses of all the four predators in NE Greenland. Using these data, we assess the impact of predation on the dynamics of the collared lemming with a 4 yr cycle and &gt;100‐fold difference between maximum and minimum densities. All predator species feed mostly (&gt;90%) on lemmings when lemming density is &gt;1 ha−1, but the shapes of the predators’ responses vary greatly. The snowy owl (Nyctea scandiaca) is present and breeds only when lemming densities at snowmelt are &gt;2 ha−1, giving rise to a step‐like numerical response. The long‐tailed skua (Stercorarius longicaudus) has a type III functional response and shifts from alternate food (mainly berries and insects) to lemmings with increasing lemming density. The skua surpasses all the other predators in summer by its total response. The type III functional response of the Arctic fox (Alopex lagopus) starts to increase at much lower lemming densities than the responses of the avian predators, but it has only a weak numerical response. Finally, the stoat (Mustela erminea) is the most specialized predator and the only one with a clearly delayed numerical response. According to their specific functional and numerical responses, each predator plays a key role at some point of the lemming cycle, but only the stoat has the potential to drive the lemming cycle. Stoat predation is greatly reduced in the winter preceding the lemming peak, and it reaches a maximum in the winter preceding the lowest lemming summer density. Stoat predation appears to maintain low lemming densities for at least two successive years. Our study provides empirical support for the specialist predator hypothesis about small mammal population cycles.

OCCURRENCE AND DISTRIBUTION OF SMALL MAMMALS ON THE GOODNEWS RIVER, SOUTHWESTERN ALASKA

A paucity of data exists on the occurrence, distribution, and abundance of small mammal communities in southwestern Alaska. To add to the understanding of these communities we conducted a comprehensive small mammal survey in southwestern Alaska. We trapped small mammals along the Goodnews River in Togiak National Wildlife Refuge from 26 June to 5 September 1996. Objectives of our study were to determine what small mammal species occur in the Goodnews River area, to determine species distribution in 4 representative habitats during 3 time periods, and to determine ideal time periods to trap small mammals in order to maximize the diversity of species encountered and the number of specimens captured. In 3600 trap-nights we captured 468 specimens including masked shrew (Sorex cinereus), pygmy shrew (S. hoyi), Alaska tiny shrew (S. yukonicus), tundra shrew (S. tundrensis), tundra vole (Microtus oeconomus), red-backed vole (Clethrionomys rutilus), Greenland collared lemming (Dicrostonyx groenlandicus), and brown lemming (Lemmus trimucronatus). The pygmy shrew, Alaska tiny shrew, Greenland collared lemming, and brown lemming are the 1st representatives of these species from the region to be placed in a museum collection. The willow habitat supported the greatest number of specimens captured (n = 170), while the wet tundra habitat yielded the greatest number of species captured (n = 4). The fall trap period (26 August to 5 September) yielded the greatest number of specimens captured (n = 229), while the spring (26 June to 6 July) and summer trap periods (26 July to 5 August) yielded greatest species diversity. Findings of rare and uncommon species illustrate the need to conduct additional surveys in the region.

LATE PLEISTOCENE LEMMINGS (LEMMUS TRIMUCRONATUS AND DICROSTONYX GROENLANDICUS; MURIDAE: RODENTIA) FROM ALBERTA, CANADA

Abstract A gravel quarry near Edmonton, Alberta, Canada, yielded remains of micromammalian taxa not previously reported in the mid-Wisconsinan (late Pleistocene) interstadial “local fauna.” A left M1 and an upper incisor fragment of Lemmus trimucronatus and a left M2 of Dicrostonyx groenlandicus were recovered. These finds represent the 2nd Pleistocene record for Lemmus in Alberta, the 3rd for Dicrostonyx, and the 1st for both taxa from a northern Great Plains site. They help to fill distributional gaps between Beringia and the midcontinent. In association with those of large grazing megaherbivores, these new arvicoline finds support the inference of a cool, fairly dry steppe in central Alberta during the last interstadial.

HERBIVORE FUNCTIONAL RESPONSE IN HETEROGENEOUS ENVIRONMENTS: A CONTEST AMONG MODELS

Variation in the spatial arrangement of plant tissue modifies the functional response of herbivores. In heterogeneous environments, this variation can occur at multiple spatial scales. We used likelihood-based approaches to examine the strength of evidence in data for models of herbivore functional response to spatial variation in plants. These models represented different hypotheses about plant characteristics controlling intake rate, including biomass, bite mass, plant density, and the composite effects of plant density and bite mass. Models were fit to observations of the food intake rate of elk (Cervus canadensis), white-tailed deer (Odocoileus virginianus), prairie dogs (Cynomys ludovicianus), domestic rabbits (Oryctolagus cuniculus), and lemmings (Dicrostonyx groenlandicus) feeding in plant patches where plant density and plant mass ranged over at least two orders of magnitude. The model representing composite effects of bite mass and plant density had more support in the data than any competing mod...

Catechin content and consumption ratio of the collared lemming.

Chemical- plant defences as mechanisms affecting herbivore populations have been debated during the past decade. Several authors have questioned the hypothesis, but the present study shows that collared lemmings ( Dicrostonyx groenlandicus) in northeast Greenland prefer food plants with a lower catechin content. Dicrostonyx species are known to have specialised on shrubs, especially Dryas spp. and Salix spp., rather than graminoids like other related microtines. Bioassays were conducted using food material from Dryas spp., Salix arctica, Vaccinium uliginosum, Kobresia myosuroides and Poa glauca. Enclosures with the first three species mentioned were further treated by clipping to simulate herbivory in order to induce the production of the plant defence compound catechin. Treatment increased the catechin content in Dryas spp., S. arctica (females only) and V. uliginosum significantly compared with the catechin concentration in untreated plants. These elevated catechin concentrations had a significantly negative effect on the consumption rate of Dryas spp. and female S. arctica by collared lemmings.

The summer decline of the collared lemming, Dicrostonyx groenlandicus, in high arctic Greenland

I studied the population structure and dynamics of the collared lemming, Dicrostonyx groenlandicus Traill, on Traill Island (NE Greenland) in 1998 to 2000. This is the first comprehensive study of a Greenlandic collared lemming population. During this period, population density continuously declined (&gt;100 fold‐decrease) from more than 10 ind/ha (peak year 1998) to less than 0.1 ind/ha (low year 2000), with the exception of one period of increase in the winter 1998–99. Several population parameters were correlated with these changes in density. Average body mass was greater in the peak year than in the intermediate year (1999) and greater in August than in July in both years. Growth rates were only positive in 1998 and only for young lemmings. Females had unexpectedly larger home ranges than males and were more mobile than males during the decline phase (1999). Poor recruitment and high predation rates (up to 3.4% per day for females in 1998) were the proximate causes of the summer declines in the study area. A simple calculation shows that even with a maximal rate of increase, this lemming population would not have been able to compensate for the high predation rate, and hence it necessarily faced a predation‐induced summer decline during the part of population oscillation studied.

Multiple glacial refugia in the North American Arctic: inference from phylogeography of the collared lemming (Dicrostonyx groenlandicus).

Cryptic northern refugia beyond the ice limit of the Pleistocene glaciations may have had significant influence on the current pattern of biodiversity in Arctic regions. In order to evaluate whether northern glacial refugia existed in the Canadian Arctic, we examined mitochondrial DNA phylogeography in the northernmost species of rodents, the collared lemming (Dicrostonyx groenlandicus) sampled across its range of distribution in the North American Arctic and Greenland. The division of the collared lemming into the Canadian Arctic and eastern Beringia phylogroups does not support postglacial colonization of the North American Arctic from a single eastern Beringia refugium. Rather, the phylogeographical structure and sparse fossil records indicate that, during the last glaciation, some biologically significant refugia and important sources of postglacial colonization were located to the northwest of the main ice sheet in the Canadian Arctic.

Metabolic rate and thermal conductance of lemmings from high-arctic Canada and Siberia.

The arctic climate places high demands on the energy metabolism of its inhabitants. We measured resting (RMR) and basal metabolic rates (BMR), body temperatures, and dry and wet thermal conductances in summer morphs of the lemmings Dicrostonyx groenlandicus and Lemmus trimucronatus in arctic Canada, and the BMR of D. torquatus, D. groenlandicus, L. sibiricus, L. bungei and L. trimucronatus in Siberia. In contrast to previous studies the data were collected on animals that had spent only a limited time in captivity. All parameters were analysed in relation to the variations in body mass (20-90 g). Body temperature and BMR were lower in D. groenlandicus than L. trimucronatus, which coincides with greater longevity in the former species. Wet and dry thermal conductances of both species were similar and comparable with those of other Myomorpha (mouse-type rodents), indicating no evidence for a previously claimed lower thermal conductance in lemmings. BMR in lemmings appeared to be higher than in other Arvicolidae (voles, lemmings and muskrats), which could relate to their typically high-latitude distribution. However, the more southerly living Lemmus species had higher BMR than the more northerly living Dicrostonyx species, which may be explained by the former having a relatively low-quality diet.

The influence of body mass on daily movement patterns and home ranges of the collared lemming (Dicrostonyx groenlandicus)

While the determinants of animals' space use have been addressed in a large number of studies, its intrasexual variability has received only limited attention. By means of radiotelemetry we found body mass to influence home-range size and distance moved by adult collared lemmings (Dicrostonyx groenlandicus) in northeast Greenland. Male body mass was positively correlated with home-range size. Distance moved by both males and females was also correlated with body mass, but with opposite trends: male movement distances increased with body mass, while female movement distances decreased. This may reflect the fact that larger females occupy the most favourable habitats, i.e., the habitats that minimize the need for movement, and thus exposure to predators, without limiting the food supply. The variability in male home range size and distance moved resulted in variability in the number of females accessible to each male. Larger males had access to more females, and hence, body mass was indirectly important for individual mating opportunities. However, increasing access to females was associated with higher costs in terms of mass loss, probably as a consequence of increased energy requirements and exposure to predators.

Safety of lyophilized SAG2 oral rabies vaccine in collared lemmings.

Fifteen collared lemmings (Dicrostonyx groenlandicus) were exposed to a lyophilized oral rabies vaccine designed to immunize wild carnivore populations. No animals contracted rabies from the vaccine as determined by the absence of clinical signs after 37 days and lack of rabies virus in brain tissue determined by the fluorescent antibody (FA) test. These results suggest that collared lemmings would not contract rabies if they ingested this lyophilized vaccine in the wild during bait vaccination programs for arctic foxes (Alopex lagopus).