The Herbivore-Based Trophic System 403 



summer caribou take equal amoums of the aboveground parts of dicoty- 

 ledons and graminoids, about 15 to 20% of which may be dead material. 

 During winter caribou in the Prudhoe Bay region probably take mostly 

 dead plant material. Dicrostonyx specialize on dicotyledons, mostly Salix 

 spp., throughout the year, but graminoids form a supplement of about 

 10 to 20"7o of their diet (Batzli 1975a). Ground squirrels eat primarily 

 vegetative and reproductive parts of dicotyledons (Batzli and Sobaski 

 1980). The combined effects of these diets are that graminoids are most 

 heavily grazed on the coastal tundra at Barrow, while dicotyledons usual- 

 ly receive equal, if not more, grazing pressure than graminoids in the 

 Prudhoe Bay region. 



Impact on Habitat 



Five major characteristics of the grazing systems in the coastal tun- 

 dras at Barrow and Prudhoe Bay can be compared (Table 10-12). Be- 

 cause small mammals at Barrow have been more intensively studied dur- 

 ing the International Biological Program and because the literature on 



TABLE 10-12 



Comparison of Mammalian Grazing Systems in the 

 Coastal Tundras at Barrow and Prudhoe Bay 



Characteristic 



Barrow 



Prudhoe Bay 



1. Diversity of grazers 



2. Dominant grazer 



a. Biomass 



b. Consumption 



3. Grazing pressure 



a. Annual 



b. Seasonal 



4. Forage taken 



5. Major impacts of grazers 



a. Microtopography 



b. Vegetation 



c. Soil 



Two species 

 One family 

 One order 



Lemmings (Lemmus) 

 Lemmings (Lemmus) 



Light to heavy (cyclic) 

 Winter > summer 

 Graminoids and mosses 



Burrows, runways and 

 hummock formation. 



Favor graminoids and in- 

 crease productivity. 



Speed nutrient cycling, in- 

 crease depth of thaw and 

 change dispersion pat- 

 terns of nutrients. 



Four species 

 Three families 

 Two orders 



Caribou (Rangifer) 

 Lemmings (Dicrostonyx and 

 Lemmus) and caribou 



Light to moderate (stable) 

 Winter = summer 

 Graminoids and dicotyledons 



Trampling, trails and 



burrows. 

 Undocumented. 



Undocumented. 



