Analysis of estimates of population size of ringed s,eals (Phoca hispida) and polar bears (Ursus maritimus) from several areas indicated that estimates of one predicted the range of expected population size of the other in areas where ringed seals constitute the primary prey. In some areas, the closeness of this relationship indicates where estimates of either seals or bears may be inaccurate. The number of seals required to support a population of polar bears of predetermined size was estimated independently using both behavioral and energetic data. Behavioral estimates of the number of seals killed may overestimate energetic requirements and vice versa. Predation and energy matrices indicated that high levels of predation on seals are sustainable only if most animals killed are young-of-the-year. The field metabolic rate of the polar bear appears to be about twice the basal metabolic rate. Densities of seals vary in response to overall productivity of the ecosystem in different areas, and fluctuations in their numbers and reproductive rates between years can be used to monitor changes in productivity of the ecosystem. These changes also cause variation in productivity of bears, which indicates the sensitivity, at the population level, of the relationship between ringed seals and polar bears.

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During recent decades there has been a change in the circulation of atmospheric pressure throughout the Northern Hemisphere. These variations are expressed in the recently described Arctic Oscillation (AO), which has shown an upward trend (associated with winter warming in the eastern Arctic) during the last three decades. We analysed a 12-year time series on growth of Cassiope tetragona (Lapland Cassiope) and a 21-year time series on abundance of a Svalbard reindeer population. High values of the AO index were associated with reduced plant growth and reindeer population growth rate. The North Atlantic Oscillation index was not able to explain a significant proportion of the variance in either plant growth or reindeer population fluctuations. Thus, the AO index may be a better predictor for ecosystem effects of climate change in certain high-arctic areas compared to the NAO index.

The relative contribution of density‐dependent and density‐independent factors on variation in the population growth rate of an introduced population Svalbard reindeer was studied by time series analysis. No significant effects of either direct or delayed density‐dependence were found. Annual variation in population growth rate was strongly negatively related to amount of precipitation during winter (i.e. high growth rates occurred when winters were dry). There was no significant relationship between the NAO‐index and the population growth rate. However, there was an interaction between population density and the climatic variables, i.e. the effect of climate was stronger at high densities. These results support the view that population fluctuations of arctic ungulates are strongly influenced by stochastic variation in climate.

The distribution of blubber in ringed seals (Phoca hispida) and relationships between surface area, body mass, and linear dimensions are described. The blubber was distributed in such a way that the ratio of blubber thickness to body radius is nearly constant over the body, maximizing the available blubber for insulation. The hind part of the body has a higher thickness to radius ratio and is thus "overinsulated." During periods of mass loss, fat is lost fastest from this overinsulated region, thus reducing the negative thermal effects of the fat loss. We present formulae for calculating body surface area and an effective, or "equivalent blubber thickness," for calculations of heat loss and suggest that these formulae are independent of size and shape. By combining these equations, we arrive at a general formula for calculating a lower limit for heat loss from marine mammals. According to this formula, thermal stability can be maintained when blubber is lost if mass is simultaneously lost from the body core.