394 



G. O. Batzli et al. 



^ 60 



« 



i 50 

 o 



.88 



- a 



a. 



>< 



c 

 o 



<u 



> 



c 

 o 



3 



o 



o 

 o 



3 



(0 



Q 



0) 



1 — r 



1 — I — r 



|3l^-| 



Group Size 

 (•)0-lO 

 (o)>IOO 



60 



50 

 40 

 30 

 20 

 10 



-b. 



2,9 

 I- O 



-I — I — I — I — I — r 



Group Size 



011-20 

 (0)21-99 



T — I — I — r 



/ 



/ 



/ 



/ 



/ 



/ 



/ 



/ 



/ 



— 2,9 



16 ,12 / 



/ 



3,4 



O 



3,4 



/ 



I6« ^ 



— / OI2 



1 / I I I I 



1 I I 



2 4 6 8 10 12 



Relative Availability of Digestible Forage 



FIGURE 10-22. The rela- 

 tionship of the distribution 

 of caribou among habitats to 

 the estimated relative availa- 

 bility of digestible forage for 

 those habitats when under no 

 insect attack (a) or mild to se- 

 vere attack (b). The numbers 

 refer to habitat types given in 

 Figure 10-16. (After White et 

 al. 1975.) 



To investigate the possible influence of food quality on factors reg- 

 ulating food intake a model of caribou rumen function (rumenmet) was 

 constructed (White et al. 1981). The model interfaced factors regulating 

 food intake with factors responsible for digestion and outflow from the 

 rumen. The rumination time required to reduce the particle size of unfer- 

 mented material, so that it could leave the rumen, limited the amount of 

 time available for grazing, particularly when forage digestibility was low. 

 Thus, although the availability of green plant biomass regulates the actu- 

 al eating rate, the digestibility of the food controls the amount of time 

 the animal must ruminate and the amount of time left for grazing. Re- 

 sults from the model indicated that daily food intake may ultimately be 

 regulated by the digestibility of the diet of caribou, a result well docu- 

 mented for domestic ruminants (Baumgardt 1970, Baile and Mayer 

 1970). 



Seasonal changes in available plant biomass and digestibility of for- 



M 



