The Herbivore-Based Trophic System 347 



Although collared lemmings are not abundant on the coastal tundra 

 at Barrow, they are more common than brown lemmings at many other 

 tundra sites (Bee and Hall 1956, Krebs 1964, Fuller et al. 1975, Batzli and 

 Jung 1980), and they present an interesting contrast. Collared lemmings 

 generally prefer higher, drier habitats than brown lemmings, particularly 

 areas where dicotyledonous plants are common. They excavate more 

 elaborate burrow systems than brown lemmings and do not use runways, 

 which are not required in habitats without dense graminoid growth. 



Nutrition and Energetics 



Diet 



The food habits of lemmings, as of most herbivores, vary with sea- 

 son and habitat. In general, however, collared lemmings and brown lem- 

 mings specialize on different food types. Collared lemmings take primar- 

 ily dicotyledons supplemented by graminoids, whereas brown lemmings 

 take primarily graminoids supplemented by mosses. Salix appears to be 

 the most important dietary item of collared lemmings in summer (40 to 

 50%) and may be even more important in winter. Dicrostonyx feces from 

 winter nests contain large amounts of willow leaves. Dietary specializa- 

 tion reflects more than differences in habitat preference because dietary 

 compositions remain distinct even at sites where both species occur 

 (BatzH 1975a). 



We have examined the food habits of brown lemmings in some de- 

 tail. Significant seasonal changes in diet occur, from about 80<Vo gramin- 

 oids in mid-summer to 55% in mid-winter. Changes with habitat appear 

 to be greater in summer than winter. During July graminoids may con- 

 tribute only 70% of the diet in polygonal terrain but over 90% in low, 

 wet meadows. During winter the variation of graminoid content between 

 habitats is only ±5%. Dicotyledonous plants make up a fairly consistent 

 5 to 10% of the diet, and Hchens contribute less than 1%; thus, most of 

 the shifting to and from graminoids is matched by opposite trends for 

 mosses. 



Selection among graminoid species has been examined in the labora- 

 tory by Melchior (pers. comm.). Lemmings selected the sedges Eriophor- 

 um russeolum and E. scheuchzeri in greater amounts than other species 

 when offered a choice of graminoid species in the form of sod blocks. 

 Naturally occurring dicotyledonous species were ignored or consumed in 

 very small amounts. Living green leaves and leaf sheaths were consumed; 

 dead plant parts were rejected. Inflorescences were consumed by some 

 lemmings and rejected by others. Thompson (1951) reported similar 

 results; Lemmus preferred sedges and grasses and Dicrostonyx preferred 



