Variations in Seasonal Nutrition, Thermoregulation and Water Balance in Two New Zealand Populations of the Common Brushtail Possum, Trichosurus Vulpecula (Phalangeridae).

Two populations of common brushtail possum, at Wanganui in the North Island of New Zealand and Westland in the South Island, were compared in aspects of nutrition, thermoregulation and water balance at 2 thermal conditions in controlled-environment rooms. The thermal conditions and adaptation had no influence on nutrition and water balance but caused variation in bodyweight and in rates of food intake and water turnover, both relative to metabolic body size. Although the 2 populations differed greatly in body mass they had different rates of food intake relative to metabolic size, but similar individual rates. Rates of metabolized energy intake followed a similar pattern. Conversely, rates of water turnover relative to metabolic size were similar between populations but differed for individuals. The trend for differences between populations in indices of urine concentration were associated with different patterns of food and water intakes. These differences cannot be explained in terms of body mass increments. The physiological variation between populations was greatly influenced by differences in body size, which accord with Bergmann's rule. The larger size of the Westland animals is advantageous during abstinence from feeding during frequent foul weather, and the smaller size of the Wanganui animals confers advantages in water balance during annual periods of prolonged rainfall deficiency.