Geographic clines in body weight of Norwegian red deer: a novel explanation of Bergmann's rule?

Variation in body weight of red deer in Norway was investigated along two climatic gradients: one with increasing latitude, and the other with proximity to the coast. Deer of all sex/age classes were significantly heavier in the northern parts of their range compared with the south and were also significantly heavier at inland localities compared with the coast. Body weights were negatively correlated with temperature and precipitation throughout the years. These clines in body weight apparently support Bergmann's rule, and may reflect selection for large size in cold environments. However, we interpret the results in the light of recent work on plant physiology which indicates higher quality forage at high latitudes, and in cooler and drier climates: conditions which are likely lo enhance growth in the north and inland. Evidence that individual deer which migrate inland, following the snow melt, are heavier is also presented and discussed in terms of an adaptive behaviour that maximises the intake of digestible energy and high quality nutrients.