HART 

 Non- aquatic Fur Bearers 



The large fur-bearing mammals have been investigated by 

 American and Russian investigators. The best known work on this 

 subject was published by Scholander et al. (1950a, b, and c), who 

 were the only workers to demonstrate the existence of true evolu- 

 tionary climatic adaptation. This demonstration was made by com- 

 paring arctic and tropical mammals with respect to metabolic rates 

 at different temperatures and with respect to pelage insulation. It 

 was found that the tropical mammals that were investigated were 

 very sensitive metabolically to lowering of ambienttemperatures, as 

 shown by an abrupt increase in oxygen consumption with lowering of 

 temperature. In contrast, the arctic mammals did not begin to in- 

 crease their metabolism until they experienced much lower tem- 

 peratures and some could virtually remain in a basal state at tem- 

 peratures down to -40 G and below. The results for the tropical 

 raccoon ( Procyon cancrivorus or lotor), the small arctic lemming, 

 and the Eskimo dog pup ( Canis familiaris ) (Figure 1) illustrate these 

 distinctions. Using Scholander 's terminology, it was observed that 

 the critical temperature and the critical gradient for increase in ox- 

 ygen consumption was lower in arctic mammals. Since the slopes of 

 the curves were extrapolated to body temperature, the lower critical 

 temperatures were associated with a smaller increase in metabolism 

 for a given drop in temperature. 



The distinction between arctic and tropical mammals was not 

 associated with differences in the resting metabolism or in body 

 temperature (Scholander, et al., 1950 b), but with differences in body 

 insulation. Arctic mammals were found to have greater pelage insu- 

 lation (Scholander, et al., 1950c) than tropical mammals (Figure 2). 



Some of the northern mammals investigated by Russian work- 

 ers, for example Ol'nyanskaya and Slonim (1947) whose work is 

 shown in Figure 3, were also relatively insensitive to cold but there 

 was a very large individual variability within each species. The in- 

 terpretation given to the data by the authors did not distinguish be- 

 tween zones of physical and chemical regulation; hence no apparent 

 critical temperatures were noted. The rabbit (Lepus timidus ) , which 

 showed an increase in oxygen consumption at temperatures below 

 20 G, differed from the Alaskan hare (Lepus americanus) studied 



204 



