The Herbivore-Based Trophic System 355 



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Temperature, "C 



FIGURE 10-9. The minimum feeding times required to 

 meet the energetic demands of different-sized lemmings 

 at several temperatures, assuming high availability of for- 

 age (no search time). Ratios of feeding times for large 

 and small lemmings are shown by the dashed line. 



lemming is the time spent foraging. Each foraging bout requires the lem- 

 ming to leave the warmth and protection of the nest or burrow and risk 

 exposure to predators and/or lower temperatures. Melchior (pers. 

 comm.) found that, with grasses and sedges provided ad libitum, mean 

 food intake (± 1 SE) was 0.14 ± 0.02 gdw min"'. At this rate, a 40-g 

 lemming could fill its stomach in slightly less than six minutes. Since no 

 search was involved this rate is limited only by handling time, and pro- 

 vides an estimate of maximum ingestion rate. Minimum daily foraging 

 time may now be calculated as a function of body weight and ambient 

 temperature (Figure 10-9): 



Min. feeding time = Stomach capacity 

 (min day"') (gdw) 



X Required energy 

 (J day-') 



Max. ingestion rate" 

 (g min"') 



Stomach capacity"' 

 (J) 



Thus, small lemmings require more separate fillings, but less time to 

 fill the gut and less feeding time even at low temperatures. Of course, 



