398 G. O. Batzli et al. 



10-3). At a density of 0.001 to 0.01 animal ha"' annual production was 

 0.24 to 0.78 MJ ha"' yr'. Energy retained, or productive energy, 

 amounted to 1% of gross energy intake, 1.8^^0 of assimilated energy, and 

 2.1% of respired energy. 



Although calves make up only 15% of the population, they con- 

 tribute 30% of the production. Seventy percent of the production is con- 

 tributed by the 0- to 3-year-old caribou, which make up only 29% of the 

 population. Thus, disturbances which affect the younger animals, e.g. 

 adverse weather conditions, poor range quality or constant predation 

 and harassment, have a marked effect on the population's productivity. 



Population energetics in caribou can be compared with previous cal- 

 culations for elephants (Loxodonta africanus — Petrides and Swank 

 1966) and white-tailed deer (Odocoileus virginianus — Davis and Golley 

 1963). Average caribou biomass (14 MJ ha"') was much lower than that 

 of elephants (297 MJ ha"') or white-tailed deer (54 MJ ha"'). Biomass 

 and population turnover are reflected in absolute production of 0.78, 14 

 and 27 MJ ha"' yr"', respectively, for the three species. However, effi- 

 ciency of production with respect to energy intake, assimilation and 

 respiration was similar for all species. 



In addition to energy, caribou must receive sufficient nutrients from 

 their forage to maintain a normal physiological state. Some insight into 

 the relative importance of various nutrients for caribou can be gained by 

 considering the degree to which nutrients in the diet must be retained. 

 Similar calculations were made for lemmings. 



TABLE 10-9 Relative Concentration of Energy (kJ gdw') 

 and Nutrients (mg gdw~') in Vascular Plants 

 and Caribou 



• Data as in Table 10-4. 



t Based on tissue values estimated for lOO-kg domestic cattle (Agricultural Research 

 Council 1965). 

 ** Estimates based on equation analogous to that used for lemmings (p. 356). 

 Note: Retention of ingested nutrients in caribou represented by ratio of production to 

 ingestion (P/1). 



I 



