392 



G. O. Batzli et al. 



200 



r 



? 160 



X) 





■o 

 o 

 o 



o 



Q 



120 



80 



40 



T 1 1 1 1 1 1 r 



-^ a A 



J 1 L 



20 40 60 80 100 



Liv/e Biomass, gdw m'^ 



FIGURE 10-20. Theoretical relationships between daily food intake and 

 the availability of live biomass of vascular plants for lactating females 

 (o), adult males (m), and non-lactating females (a). The relationships 

 were calculated as the product of the relationships shown in Figure 

 10-19. The arrows indicate the daily food intake required to maintain 

 body weight and, therefore, the amount of live biomass of available 

 plants required before the caribou would gain weight. (After White et al. 

 1975.) 



sheep and reindeer have shown that the time spent grazing decHnes as 

 available biomass increases (Allden and Whittaker 1970, Young and 

 Corbett 1972, Trudell and White 1980). The curves for adult males and 

 lactating females in Figure 10- 19b were extrapolated from the data for 

 non-lactating females. Presumably, curves for caribou would be similar. 



The theoretical relationship between daily food intake and available 

 plant biomass for reindeer can now be calculated (Figure 10-20, Trudell 

 and White 1980). Food intake for lactating reindeer exceeds that for non- 

 lactating reindeer because lactating females spend more time grazing. 

 The theoretical relationships in Figure 10-20 are similar to actual obser- 

 vations of food intake in relation to plant biomass reported for domestic 

 sheep grazing in Mediterranean grassland systems (Arnold 1964, Arnold 

 and Dudzinski 1967). 



Assuming that caribou and reindeer have similar grazing response 

 functions, food intake of caribou in the Prudhoe Bay region during sum- 

 mer is directly related to seasonal changes in standing crop of green vas- 

 cular plants, which peaks in midsummer (Chapter 3). In particular, food 

 intake declines rapidly when the availability of green biomass becomes 

 less than 40 to 50 g m'^ Maximum food intake, when green biomass is 

 greater than 50 g m'^ would be expected only for the month of July and 

 early August in Carex-Eriophorum meadows. By selecting vegetation 



