Nils Are Øritsland

Temperature regulation of the polar bear (Thalarctos maritimus)

1. 1. The polar bear has developed thermoregulatory mechanism consistent with its semiaquatic way of life. 2. 2. In vivo examinations of three adult polar bears were performed by radiotelemetry on bears in cages and by measurements on bear tied to a frame in air and in water. 3. 3. Significant insulation is achieved by means of fur, blubber and other peripheral tissues both in air and water. 4. 4. Vascular heat exchanges are present in the limbs, and two thin muscle sheets adjacent to the skin probably afford a special avenue of heat dissipation. 5. 5. Insulation and heat dissipation seems, however, insufficient during extreme weather conditions, forcing the polar bear to utilize postural increase of insulation or to slow down activity during cold or warm weather respectively.

Activity pattern of arctic reindeer in a predator-free environment: no need to keep a daily rhythm

Arctic Cervids face considerable challenges in sustaining life in a harsh and highly seasonal environment, and when to forage is a key component of the survival strategy. We predict that a cervid maximizes net intake of energy to change the duration of feeding-ruminating cycles depending on season, and pays no attention to light or other activity-entraining cues. Still, in periods of bad weather it may pay energetically to reduce exposure and heat loss. We investigated environmental impact on the seasonal and daily activity pattern of a food-limited, predator-free arctic deer, the Svalbard reindeer. We found that the reindeer indeed had season-dependent feeding-rumination intervals, with no distinct peaks in activity at sunrise and sunset, as would be expected if animals maximize energy intake rates in predator-free environments. However, they temporarily reduced activity when exposed to low temperature and increased precipitation during winter, possibly to conserve energy. We provide insight into the behavioural strategy of Svalbard reindeer which enables them to cope with such an extreme environment.

Continuous and discrete extreme climatic events affecting the dynamics of a high-arctic reindeer population

Climate at northern latitudes are currently changing both with regard to the mean and the temporal variability at any given site, increasing the frequency of extreme events such as cold and warm spells. Here we use a conceptually new modelling approach with two different dynamic terms of the climatic effects on a Svalbard reindeer population (the Brøggerhalvøya population) which underwent an extreme icing event (“locked pastures”) with 80% reduction in population size during one winter (1993/94). One term captures the continuous and linear effect depending upon the Arctic Oscillation and another the discrete (rare) “event” process. The introduction of an “event” parameter describing the discrete extreme winter resulted in a more parsimonious model. Such an approach may be useful in strongly age-structured ungulate populations, with young and very old individuals being particularly prone to mortality factors during adverse conditions (resulting in a population structure that differs before and after extreme climatic events). A simulation study demonstrates that our approach is able to properly detect the ecological effects of such extreme climate events.

Insulation of furs in water.

Abstract 1. 1. The mode of heat transfer through furs in water was examined for the polar bear and the harp seal. 2. 2. The woolly hairs of the underfur act to keep an inner water layer stagnant. 3. 3. The harp seal retain a 2 mm thick and the polar bear at 10 mm thick layer of stagnant water in the underfur. 4. 4. The insulative value of the fur in water is a significant part of the total unregulated insulation of the polar bear and of minor significance for the harp seal.

Weight loss and catabolic adaptations to starvation in grey seal pups

Five grey seal pups lost from 18 to 32% of their initial body weight during a 21 day starvation period. Blubber fat mass density was 0.93 +/- 0.03 g/cm3. A considerable loss of blubber fat was recorded, but analysis of the weight loss and body size data indicated that blubber fat was retained for thermoregulatory reasons, particularly in the lean, smaller seals. It is possible that phocid seals during periods of negative energy balance have a higher rate of protein catabolism than normal for terrestrial mammals.

Metabolic depression and heat balance in starving Wistar rats

Resting metabolic rate and heat balance was studied in rats starved for 8 days at ambient temperature 22 degrees C and 30 degrees C. A depression of the resting metabolic rate was observed, at both temperatures. Metabolic rate depression, expressed as a function of the ratio between the real body wt and the normal body wt, was less at 22 degrees C than at 30 degrees C. Deep body temperature decrements of 2 degrees C and 0.6 degrees C by the end of starvation indicated that central temperature controlling mechanisms were affected. Concurrent decrements of evaporative heat loss did not account for the changes in heat conductance, thus indicating that a reduction of peripheral blood circulation also took part.

Starvation survival and body composition in mammals with particular reference to Homo sapiens

A computer model of body mass and composition in relation to gross energy balance is constructed. The model is built using conventional empirical physiological formulae rather than statistical or analytical mathematical techniques. The model is applied to the Minnesota and other experiments and produces as good or better simulations of observed values of changes in body weight than reported for other formulae or models. Alternative physiological mechanisms concerning metabolic adaptions to starvation, changes in time activity budgets and the energy equivalents of weight loss offer equally good simulations of experimental results. The present analysis highlights the survival value of a basal metabolic depression during starvation and indicates an optimal body composition of 10% mobilizable fat for starvation survival for a 70 kg man. Proper quantification of the effects of the physiological mechanisms involved depends on new experimental data, however. Long term continuous monitoring of time activity budgets are a necessary part of such experiments.

Polar bear thermoregulation: Effect of oil on the insulative properties of fur

Abstract 1. 1.|Oil caused a substantial decrease in the insulative value of polar bear ( Ursus maritimus ) pelts measured in vitro . 2. 2.|Following oil contamination the calm air heat transfer coefficient increased by a factor of 2 to 5: the wind coefficient averaged 290% greater and the solar utilization increased by 55%. 3. 3.|Conductance through oil-covered furs remained high at winter temperatures ( T a = 0.6° C ) but decreased with time at summer temperatures ( T a = 24.7° C ). 4. 4.|The most viscous of the three oils tested had a more consistently negative effect on insulation.

Metabolic compensation in oil-exposed polar bears

Abstract 1. 1.|Metabolism and temperature were monitored for three sub-adult polar bears ( Ursus maritimus ) before and after exposure to a pool covered with 1 cm slick of Midale crude oil. 2. 2.|Deep body and skin temperatures were measured by surgically-implanted radio transmitters. 3. 3.|Metabolic rate was determined by use of an open circuit respiration chamber and measurement of oxygen uptake 4. 4.|Oil exposure resulted in the fouling of the fur. 5. 5.|In all study animals thermoregulatory problems occurred following oil exposure: the increase in metabolic rate varied from 27 to 86% after oil exposure, whereas whole body thermal conductance increased 21–55%.

Wavelength-dependent solar heating of harp seals (Pagophilus groenlandicus)

Abstract Solar heating of harp seals is probably due mainly to radiation reflected from hair to hair towards the skin.Abstract Solar heating of harp seals is probably due mainly to radiation reflected from hair to hair towards the skin.