Habitat selection,reproduction and predation of wintering lemmings in the Arctic

Snow cover has dramatic effects on the structure and functioning of Arctic ecosystems in winter. In the tundra, the subnivean space is the primary habitat of wintering small mammals and may be critical for their survival and reproduction. We have investigated the effects of snow cover and habitat features on the distributions of collared lemming (Dicrostonyx groenlandicus) and brown lemming (Lemmus trimucronatus) winter nests, as well as on their probabilities of reproduction and predation by stoats (Mustela erminea) and arctic foxes (Vulpes lagopus). We sampled 193 lemming winter nests and measured habitat features at all of these nests and at random sites at two spatial scales. We also monitored overwinter ground temperature at a subsample of nest and random sites. Our results demonstrate that nests were primarily located in areas with high micro-topography heterogeneity, steep slopes, deep snow cover providing thermal protection (reduced daily temperature fluctuations) and a high abundance of mosses. The probability of reproduction increased in collared lemming nests at low elevation and in brown lemming nests with high availability of some graminoid species. The probability of predation by stoats was density dependent and was higher in nests used by collared lemmings. Snow cover did not affect the probability of predation of lemming nests by stoats, but deep snow cover limited predation attempts by arctic foxes. We conclude that snow cover plays a key role in the spatial structure of wintering lemming populations and potentially in their population dynamics in the Arctic.     

Metabolism,thermogenesis and daily rhythm of body temperature in the wood lemming,Myopus schisticolor

Wood lemmings (Myopus schisticolor) were captured during their autumnal migration in September and October. The animals were maintained at 12°C and under 12L:12D photoperiod. Basal metabolic rate and thermogenic capacity of the wood lemming were studied. Basal metabolic rate was 3.54 ml O₂·g^-1·h^-1, which is 215–238% of the expected value. The high basal metabolic rate seems to be typical of rodents living in high latitudes. The body temperature of the wood lemming was high (38.0–38.8°C), and did not fluctuate much during the 24-h recording. The high basal metabolic rate and the high body temperature are discussed with regard to behavioural adaptation to a low-quality winter diet. Thermogenic capacity, thermal insulation and non-shivering thermogenesis of the wood lemming displayed higher values than expected: 53.0 mW·g^-1, 0.53 mW·g^-1·C^-1 and 53.2 mW·g^-1, respectively. Brown adipose tissue showed typical thermogenic properties, although its respiratory property was fairly low, but mitochondrial protein content was high compared to other small mammals. The 24-h recording of body temperature and motor activity did not reveal whether the wood lemming is a nocturnal animal. Possibly, the expression of a circadian rhythm was masked by peculiar feeding behaviour. It is concluded that the wood lemming is well adapted to living in cold-temperature climates.Abbreviations BAT brown adipose tissue; bm, body mass - BMR basal metabolic rate - C conductance - Cox cytochrome-c-oxidase - HP heat production - HP_max maximum heat production - M metabolism - NA noradrenaline - NST non-shivering thermogenesis - NST_max maximum non-shivering thermogenesis - RMR resting metabolic rate - RQ respiratory quotient - T _a anibient temperature - T _b body temperature - T _lc lower critical temperature - UCP uncoupling protein - vO₂ oxygen consumption - vO_{2 max} maximum oxygen consumption     

Reduction of metabolic rate and thermoregulation during daily torpor

Physiological mechanisms causing reduction of metabolic rate during torpor in heterothermic endotherms are controversial. The original view that metabolic rate is reduced below the basal metabolic rate because the lowered body temperature reduces tissue metabolism has been challenged by a recent hypothesis which claims that metabolic rate during torpor is actively downregulated and is a function of the differential between body temperature and ambient temperature, rather than body temperature per se. In the present study, both the steady-state metabolic rate and body temperature of torpid stripe-faced dunnarts, Sminthopsis macroura (Dasyuridae: Marsupialia), showed two clearly different phases in response to change of air temperature. At air temperatures between 14 and 30°C, metabolic rate and body temperature decreased with air temperature, and metabolic rate showed an exponential relationship with body temperature (r ²=0.74). The Q ₁₀ for metabolic rate was between 2 and 3 over the body temperature range of 16 to 32°C. The difference between body temperature and air temperature over this temperature range did not change significantly, and the metabolic rate was not related to the difference between body temperature and air temperature (P=0.35). However, the apparent conductance decreased with air temperature. At air temperatures below 14°C, metabolic rate increased linearly with the decrease of air temperature (r ²=0.58) and body temperature was maintained above 16°C, largely independent of air temperature. Over this air temperature range, metabolic rate was positively correlated with the difference between body temperature and air temperature (r ²=0.61). Nevertheless, the Q ₁₀ for metabolic rate between normothermic and torpid thermoregulating animals at the same air temperature was also in the range of 2–3. These results suggest that over the air temperature range in which body temperature of S. macroura was not metabolically defended, metabolic rate during daily torpor was largely a function of body temperature. At air temperatures below 14°C, at which the torpid animals showed an increase of metabolic rate to regulate body temperature, the negative relationship between metabolic rate and air temperature was a function of the differential between body temperature and air temperature as during normothermia. However, even in thermoregulating animals, the reduction of metabolic rate from normothermia to torpor at a given air temperature can also be explained by temperature effects.Abbreviations BM body mass - BMR basal metabolic rate - C apparent conductance - MR metabolic rate - RMR resting metabolic rate - RQ respiratory quotient - T _a air temperature - T _b body temperature - T _lc lower critical temperature - T _tc critical air temperature during torpor - TMR metabolic rate during torpor - TNZ thermoneutral zone - T difference between body temperature and air temperature - VO₂ rate of oxygen consumption     

Metabolic rates,food consumption and thermoregulation in seasonal acclimatization of the Cape porcupine Hystrix africaeaustralis

Summary Metabolic rates by means of oxygen consumption (VO₂) at various ambient temperatures (T _a) and food consumption as well as water intake and thermoregulation were compared between individuals of the Cape porcupine Hystrix africaeaustralis acclimated to T _a=32°C with a photoperiod of 16L:8D summer-acclimated and T _a=10°C; 8L:16D winter-acclimated. The lower critical temperature as well as overall minimal thermal conductance were lower for the winter-acclimated porcupines when compared to summer-acclimated ones, while VO₂ at the thermoneutral-zone was significantly (P<0.001) higher in the winter-acclimated porcupines. Dry matter intake, apparent digestible dry matter intake, gross digestible energy intake, as well as water intake, were significantly higher in the winter-acclimated porcupines. Yet, while dry matter intake increased 4 times in the winter-acclimated porcupines, apparent digestible dry matter increased only at a rate of 2.9 times. This difference is better reflected in terms of digestibility efficiency which in the winter-acclimated porcupines is only at a rate of 67.5% while in the summer-acclimated porcupines it is at a rate of 90%. From the results of this study, it is possible to assume that heat production in the winter-acclimated porcupines is partly increased by food intake. Increased heat production on the one hand, and a decrease in overall minimal thermal conductance on the other, seem to be important mechanisms in winter acclimatization of the Cape porcupine.     

Strategies of thermoregulation and foraging in two vespid wasps,Dolichovespula maculata andVespula vulgaris

Summary D. maculata, the white-faced hornet, stabilized (regulated) thoracic temperature (T _Th) over wide ranges of ambient temperature (T _a), whileV. vulgaris, the common yellowjacket, regulatedT _Th poorly. The hornets also maintained a higherT _Th than the wasps, sometimes heating 38°C aboveT _a. Attacking individuals of both species had higherT _Th than those either leaving or returning to the nest from foraging. The hornets, who are primarily hunters of live prey, showed peak activity near dawn, and they were as active atT _a=2°C as at 20°C. Being able to regulate theirT _Th and fly at the lowT _a should enhance their ability to capture small insects that are usually torpid at theseT _a. The yellowjacket wasps, on the other hand, who are scavengers as well as hunters, did not leave the nest at 2°C; their activity decreased greatly with decreasingT _a. Differences in the foraging technique of the two vespids may be related to their different abilities to thermoregulate.     

Predator‐mediated interactions between preferred,alternative and incidental prey in the arctic tundra

Apparent competition between prey is hypothesized to occur more frequently in environments with low densities of preferred prey, where predators are forced to forage for multiple prey items. In the arctic tundra, numerical and functional responses of predators to preferred prey (lemmings) affect the predation pressure on alternative prey (goose eggs) and predators aggregate in areas of high alternative prey density. Therefore, we hypothesized that predation risk on incidental prey (shorebird eggs) would increase in patches of high goose nest density when lemmings were scarce. To test this hypothesis, we measured predation risk on artificial shorebird nests in quadrats varying in goose nest density on Bylot Island (Nunavut, Canada) across three summers with variable lemming abundance. Predation risk on artificial shorebird nests was positively related to goose nest density, and this relationship was strongest at low lemming abundance when predation risk increased by 600% as goose nest density increased from 0 to 12 nests ha^?1. Camera monitoring showed that activity of arctic foxes, the most important predator, increased with goose nest density. Our data support our incidental prey hypothesis; when preferred prey decrease in abundance, predator mediated apparent competition via aggregative response occurs between the alternative and incidental prey items.     

Effect of torpor on the water economy of an arid-zone marsupial,the stripe-faced dunnart (<Emphasis Type="Italic">Sminthopsis macroura</Emphasis>)

Metabolic rate and evaporative water loss (EWL) were measured for a small, arid-zone marsupial, the stripe-faced dunnart (Sminthopsis macroura), when normothermic and torpid. Metabolic rate increased linearly with decreasing ambient temperature (T_a) for normothermic dunnarts, and calculated metabolic water production (MWP) ranged from 0.85±0.05 (T_a=30°C) to 3.13±0.22 mg H₂O g^–1 h^–1 (T_a=11°C). Torpor at T_a=11 and 16°C reduced MWP to 24–36% of normothermic values. EWL increased with decreasing T_a, and ranged from 1.81±0.37 (T_a=30°C) to 5.26±0.86 mg H₂O g^–1 h^–1 (T_a=11°C). Torpor significantly reduced absolute EWL to 23.5–42.3% of normothermic values, resulting in absolute water savings of 50–55 mg H₂O h^–1. The relative water economy (EWL/MWP) of the dunnarts was unfavourable, remaining >1 at all T_a investigated, and did not improve with torpor. Thus torpor in stripe-faced dunnarts results in absolute, but not relative, water savings.     

Factors affecting the daily rhythm of body temperature of captive mouse lemurs (<Emphasis Type="Italic">Microcebus murinus</Emphasis>)

Microcebus murinus, a small nocturnal Malagasy primate, exhibits adaptive energy-saving strategies such as daily hypothermia and gregarious patterns during diurnal rest. To determine whether ambient temperature (T_a), food restriction and nest sharing can modify the daily body temperature (T_b) rhythm, T_b was recorded by telemetry during winter in six males exposed to different ambient temperatures (T_a=25, 20, 15°C) and/or to a total food restriction for 3 days depending on social condition (isolated versus pair-grouped). At 25°C, the daily rhythm of T_b was characterized by high T_b values during the night and lower values during the day. Exposure to cold significantly decreased minimal T_b values and lengthened the daily hypothermia. Under food restriction, minimal T_b values were also markedly lowered. The combination of food restriction and cold induced further increases in duration and depth of torpor bouts, minimal T_b reaching a level just above T_a. Although it influenced daily hypothermia less than environmental factors, nest sharing modified effects of cold and food restriction previously observed by lengthening duration of torpor but without increasing its depth. In response to external conditions, mouse lemurs may thus adjust their energy expenditures through daily modifications of both the duration and the depth of torpor.     

The roles of energetics,water economy,foraging behavior,and geothermal refugia in the distribution of the bat,Macrotus californicus

Summary Energy metabolism, thermoregulation, and water flux ofMacrotus californicus, the most northerly representative of the Phyllostomidae, were studied in the laboratory using standard methods, and energy metabolism and water fluxes were studied in the field using the doubly labelled water method together with a time budget. Daily energy expenditures of free-living bats averaged 22.8 kJ during the winter study period. Approximately 60% of this was allocated to resting metabolism costs while in the primary roosts (22 h/day).Macrotus californicus is unable to use torpor. The thermoneutral zone (TNZ) in this species is narrow (33 to 40 °C) and metabolic rate increased rapidly as ambient temperature decreased below the TNZ. Basal metabolic rate was 1.25 ml O₂/g·h, or 24 J/g·h. Total thermal conductance below the TNZ. was 1.8 mW/g·°C, similar to values measured for other bats. Evaporative water loss showed a hyperbolic increase with increasing ambient temperature, and was approximately 1% of total body mass/h in the TNZ. The success of these bats as year-round residents in deserts in the southwestern United States is probably not due to special physiological adaptations, but to roosting and foraging behavior. They use geothermally-heated winter roost sites (stable year-round temperatures of approximately 29 °C) which minimize energy expenditures, and they have an energetically frugal pattern of foraging that relies on visual prey location. These seem to be the two major factors which have allowedM. californicus to invade the temperate zone.Abbreviations BMR basal metabolic rate - FMR field metabolic rate - T _a ambient temperature - T _b body temperature - T _lc,T _uc lower and upper critical temperature, respectively - TBW total body water - TNZ thermoneutral zone     

Working with what you’ve got: Changes in thermal preference and behavior in mice with or without nesting material

In laboratories mice are typically housed at ambient temperatures (T_a) of 20-24 °C, which are below their average preferred T_a of ≈30 °C. Adjusting laboratory T_a is not a solution because preferences differ depending on activity, time of the day, and gender. We tested the hypothesis that providing mice with nesting material will allow behavioral thermoregulation and reduce aversion to colder T_a. We housed C57BL/6J mice with and without nesting material in a set of 3 connected cages, each maintained at a different T_a (20, 25, or 30 °C). Mice were confined in and given free access to the T_a options to determine if thermotaxis or nest building was the primary mode of behavioral thermoregulation. As predicted, nesting material reduced aversion to 20 °C but the overall preference, in both treatments, was still 30 °C. Inactive and nesting behaviors were more likely to be seen in contact with nesting material while active behaviors were more likely to be observed when not in contact. Nest quality increased with decreasing T_a when mice could not use thermotaxis but nest quality was uncorrelated with T_a when thermotaxis was possible. Males decreased nest quality with increasing temperatures but females showed no correlation. We conclude that nesting material does not alter thermal preferences for 30 °C when thermotaxis is possible, indicating thermotaxis as the primary mode of behavioral thermoregulation. However, when thermotaxis is not possible, mice adjust nest shape depending on the T_a. Nesting material appears to partially compensate for cooler T_a and is especially important when mice are inactive. Therefore, nesting material may be a solution to the mismatch between laboratory T_a and mouse thermal preferences.     

Ground cavity nest temperatures and their relevance to Blue Swallow Hirundo atrocaerulea conservation

Blue Swallows Hirundo atrocaerulea are Critically Endangered within South Africa. They nest in natural underground holes in mist-belt grasslands. Temperature dataloggers were used to record ground cavity nest (T_n) and ambient temperature (T_a) for one artificial and 11 natural Blue Swallow nests. Mean ground cavity T_n was significantly different to mean T_a. T_n ranged from 17.0 ± 0.1 °C to 28.5 ± 0.3 °C and varied less than T_a (14.0 ± 0.2 to 47.7 ± 0.4 °C). Mean ground cavity T_n averaged 3.3 ± 0.9 °C warmer than mean T_a for 58% of nests, and mean T_a averaged 2.6 ± 0.5 °C warmer than mean ground cavity T_n for 42% of nests. There was no significant difference in mean ground cavity T_n for the aardvark-excavated holes (22.7 ± 1.6 °C) and sinkholes (21.5 ± 1.2 °C). Blue Swallows also nest in man-made holes, potentially a way to increase nesting sites. Mean aardvark-excavated T_n (19.2 ± 0.1 °C) was significantly warmer than mean artificial cavity T_n (18.5 ± 0.2 °C). Further investigation of breeding success of Blue Swallows in relation to T_n, incubation strategies and predation risk needs to be addressed in future studies for a better understanding of their reproductive ecology.     

The thermal and energetic significance of clustering in the speckled mousebird,Colius striatus

Summary The effect of clustering behaviour on metabolism, body temperature, thermal conductance and evaporative water loss was investigated in speckled mousebirds at temperatures between 5 and 36°C. Within the thermal neutral zone (approximately 30–35 °C) basal metabolic rate of clusters of two birds (32.5 J·g^-1·h^-1) and four birds (28.5 J·g^-1·h^-1) was significantly lower by about 11% and 22%, respectively, than that of individuals (36.4 J·g^-1·h^-1). Similarly, below the lower critical temperature, the metabolism of clusters of two and four birds was about 14% and 31% lower, respectively, than for individual birds as a result of significantly lower total thermal conductance in clustered birds. Body temperature ranged from about 36 to 41°C and was positively correlated with ambient temperature in both individuals and clusters, but was less variable in clusters. Total evaporative water loss was similar in individuals and clusters and averaged 5–6% of body weight per day below 30°C in individuals and below 25°C in clusters. Above these temperatures total evaporative water loss increased and mousebirds could dissipate between 80 and 90% of their metabolic heat production at ambient temperatures between 36 and 39°C. Mousebirds not only clustered to sleep between sunset and sunrise but were also observed to cluster during the day, even at high ambient temperature. Whereas clustering at night and during cold, wet weather serves a thermoregulatory function, in that it allows the brrds to maintain body temperature at a reduced metabolic cost, clustering during the day is probably related to maintenance of social bonds within the flock.Abbreviations BMR basal metabolic rate - bw body weight - C _totab total thermal conductance - EWI evaporative water loss - M metabolism - RH relative humidity - T _a ambient temperature - T _b body temperature - T _ch chamber temperature - T _cl cluster temperature - TEWL total evaporative water loss - LCT lower critical temperature - TNZ thermal neutral zone     

The emergence of endothermy in the black-footed and Laysan albatrosses

Eggs with pip-holes of the black-footed (Diomedea nigripes) and Laysan (Diomedea immutabilis) albatrosses were exposed to various air temperatures in the range 20–35°C in order to detect signs of incipient endothermy in late embryos. No evidence of endothermy was found. In contrast, the O₂ consumption of most hatchlings increased in response to cooling, the O₂ consumption at an air temperature of 25° C exceeding that between 34 and 35°C by 40%. In a minority of hatchlings this response was not seen. It was suggested that endothermy may develop at some time during the 24 h after hatching.Abbreviations bm body mass - C _total total thermal conductance of tissues and plumage - f respiratory frequency - FE_{O 2} fractional concentration of oxygen in air leaving chamber - FI_{O 2} fractional concentration of oxygen in air entering chamber - T _a an temperature - T _b deep-body temperature - V air-flow rate - VO₂ oxygen consumption     

Energy metabolism,body-temperature and breathing parameters in nontorpid blue-naped mousebirdsUrocolius macrourus

Summary Breathing frequencyF _r of resting blue-naped mousebirdsUrocolius macrourus lies between 50–70 per min and correlates directly with ambient temperatureT _a and energy metabolismM. The nocturnal mean energy intake per breath varies between 5.6–17.7 mJ/g. At highT _a the birds show gular fluttering with a relatively constantF _r of about 460 min^–1.M shows a constant absolute day-night difference of 25 J/g·h; the relative differences areT _a-dependent between 36–168% (lower values at lowerT _a). Thermal conductance is 2.10–2.15 J/g·h·°C (predicted 2.67), indicating a good insulation. Basal metabolic rate BMR is reduced by 63% compared to predicted values. At aT _a-range of +8–36 °C the birds are normothermic. Below this range nocturnalT _b andM decrease slightly with fallingT _a. The birds show partial heterothermia (shallow hypothermia). Clustering is an effective energy saving strategy which allows loweringM with keeping highT _b even at lowT _a.Oxygen-intake is controlled byF _r as well as by tidal volumeV t inT _a-dependent changing portions.V T can vary between 0.29–0.91 ml (mean value 49.7 ml).Abbreviations T _a ambient temperature - T _b body temperature - M energy metabolism - F _r breathing frequency - V T tidal volume - BMR basal metabolic rate - TNP thermoneutral point     

Body temperature and thermoregulation in two species of yellowjackets,Vespula germanica and V. maculifrons

In spite of the abundance and broad distribution of social wasps, little information exists concerning thermoregulation by individuals. We measured body temperatures of the yellowjackets Vespula germanica and V. maculifrons and examined their thermoregulatory mechanisms. V. germanica demonstrated thermoregulation via a decreasing gradient between thorax temperature and ambient temperature as ambient temperature increased. V. maculifrons exhibited a constant gradient at lower ambient temperatures but thorax temperature was constant at high ambient temperatures. Head temperature exhibited similar patterns in both species. In spite of low thermal conductances, a simple heat budget model predicts substantial heat loads in warm conditions in the absence of thermoregulation. Both species regurgitated when heated on the head. A smaller volume of regurgitant was produced at lower head temperatures and a larger volume at higher head temperatures. Small regurgitations resulted in stabilization of head temperature, while large ones resulted in 4°C decreases in head temperature. Regurgitation was rare when wasps were heated upon the thorax. Abdomen temperature was 3–4°C above ambient temperature, and approached ambient temperature under the hottest conditions. No evidence was found for shunting of hot hemolymph from thorax to abdomen as a cooling mechanism. The frequency of regurgitation in workers returning to the nest increased with ambient temperature. Regurgitation may be an important thermoregulatory strategy during heat stress, but is probably not the only mechanism used in yellowjackets.Abbreviations M _b body mass - M _th thorax mass - T _a ambient temperature - T _ab abdomen temperature - T _b body temperature - T _h head temperature - T _th thorax temperature - C _t thermal conductance     

Lemming winter habitat choice: a snow-fencing experiment

The insulative value of early and deep winter snow is thought to enhance winter reproduction and survival by arctic lemmings (Lemmus and Dicrostonyx spp). This leads to the general hypothesis that landscapes with persistently low lemming population densities, or low amplitude population fluctuations, have a low proportion of the land base with deep snow. We experimentally tested a component of this hypothesis, that snow depth influences habitat choice, at three Canadian Arctic sites: Bylot Island, Nunavut; Herschel Island, Yukon; Komakuk Beach, Yukon. We used snow fencing to enhance snow depth on 9-ha tundra habitats, and measured the intensity of winter use of these and control areas by counting rodent winter nests in spring. At all three sites, the density of winter nests increased in treated areas compared to control areas after the treatment, and remained higher on treated areas during the treatment. The treatment was relaxed at one site, and winter nest density returned to pre-treatment levels. The rodents’ proportional use of treated areas compared to adjacent control areas increased and remained higher during the treatment. At two of three sites, lemmings and voles showed significant attraction to the areas of deepest snow accumulation closest to the fences. The strength of the treatment effect appeared to depend on how quickly the ground level temperature regime became stable in autumn, coincident with snow depths near the hiemal threshold. Our results provide strong support for the hypothesis that snow depth is a primary determinant of winter habitat choice by tundra lemmings and voles.     

Thermoregulation in resting and active polar bears

Summary Polar bears (Ursus maritimus) regulate their body temperatures both physiologically and behaviourally proportional to their level of activity while within the thermoneutral zone. Core temperatures (T _c=36.9±0.5°C at rest) varied with the 4^th power of walking speed for the two subadult (220 kg) bears tested, whereas subcutaneous temperatures (T _sk=35.3±2.2°C at rest) were closely correlated withT _c but also varied with wind speed (v _a) and ambient temperature (T _a). Radiative fur temperatures (T _r) were closely correlated withT _a and negligibly withT _sk. Predictive equations for these temperature relationships were derived by regression analysis. Maximum rates of heat storage (S _max) were above that predicted from the literature implying that the polar bear is an energetically costly walker. Radiative heat losses of a resting polar bear amount to between 36–67% of the metabolism and assuming a respiratory heat loss of 7–10%, convective heat losses (by difference) would thus range from 33–64%. When walking, the cooling of the fur surface by forced convection and the pendulum effect of the moving legs of the bear lead to estimated convective heat losses on the order of 75% of the heat production while radiative losses are reduced to 13–22%. Increasing wind speeds enhance further this reciprocal effect.     

The effect of ambient temperature on the relationship between ventilation and metabolism in a small parrot (Agapornis roseicollis)

Summary Values for basal metabolism, standard tidal volume (V _T), standard minute volume ( ), and mean extraction efficiency (EO₂) in the thermal neutral zone (TNZ) inAgapornis roseicollis (1.84 ml·min^–1; 0.95 ml·br^–1, STPD; and 33.3 ml·min^–1, STPD; and 22.5%; respectively) were all very similar to values for these parameters previously measured inBolborhynchus lineola, a similarly sized, closely related species from a distinctly different habitat.Having both a lower critical temperature (T_lc) below and an upper critical temperature (T_uc) above those ofB. lineola, the TNZ ofA. roseicollis extended from 25° to at least 35°C. The thermal conductance below the TNZ ofA. roseicollis was 14% less than that ofB. lineola. Therefore, at 5°C the standard metabolic rate (SMR) of the former is 17% less than that of the latter, and at 35°C it is 20% less. At 5°CA. roseicollis has a lower EO₂ and at 35°C a higher EO₂ than that ofB. lineola. The patterns of resting energy metabolism and of ventilation ofA. roseicollis and ofB. lineola are consistent with the former species being better suited to living in a more variable thermal environment than the latter.MeanV _T has a weak positive correlation with the rate of oxygen consumption ( ) at a constant ambient temperature (T _a) but a much stronger correlation when resting increases in response to a decrease inT _a.V _t is the only ventilatory parameter which is linearly correlated toT _a from 35° to –25°C. The data suggest thatT _a may have a regulatory effect onV _T somewhat independent of or .     

The effect of temperature on the pattern of torpor in a marsupial hibernator

Physiological variables of torpor are strongly temperature dependent in placental hibernators. This study investigated how changes in air temperature affect the duration of torpor bouts, metabolic rate, body temperature and weight loss of the marsupial hibernator Burramys parvus (50 g) in comparison to a control group held at a constant air temperature of 2°C. The duration of torpor bouts was longest (14.0±1.0 days) and metabolic rate was lowest (0.033±0.001 ml O₂·g^-1·h^-1) at2°C. At higher air temperatures torpor bouts were significantly shorter and the metabolic rate was higher. When air temperature was reduced to 0°C, torpor bouts also shortened to 6.4±2.9 days, metabolic rate increased to about eight-fold the values at 2°C, and body temperature was maintained at the regulated minimum of 2.1±0.2°C. Because air temperature had such a strong effect on hibernation, and in particular energy expenditure, a change in climate would most likely increase winter mortality of this endangered species.Abbreviationst STP standard temperature and pressure - T _a air temperature - T _b body temperature - VO₂ rate of oxygen consumption     

Photoperiodic effects on post-weaning growth and food consumption in the collared lemming Dicrostonyx groenlandicus

The effects of long 'summer' (22L:2D) and short 'winter' (2L:22D) photoperiod on post-weaning growth and food consumption of the collared lemming were examined. Growth was described by Gompertz equations. After 10 weeks, lemmings maintained under short photoperiods developed white winter pelage and heavy bifid claws; body mass and estimated asymptotic mass were significantly greater than for lemmings reared under long photoperiod. Sexual dimorphism in body size was observed within treatments, males growing larger than females. There were no significant differences in the overall growth rate constant k as a result of either sex or photoperiod treatment. However, instantaneous growth rates (dW/dt) were significantly higher in 'winter' lemmings. Mass at weaning was a significant determinant of adult mass at 90 days.
Cumulative food consumption at 90 days was not significantly different between photoperiod groups, even though 'winter' lemmings gained more than double the mass of their 'summer' counterparts over the post-weaning period. Increased gut length observed for winter morphs may act as the physiological mechanism promoting greater gross energy efficiency.
The present study suggests that the overwintering strategy of the collared lemming with respect to body mass changes and energy requirements differs considerably from that of other microtines.