The Herbivore-Based Trophic System 387 



sand, and the animals migrate south to the wintering grounds during Oc- 

 tober through December. Groups of the Central Arctic herd overwinter 

 on the Coastal Plain and northern Foothills. Occasionally an early snow- 

 fall in the Brooks Range prevents the migration of most of the caribou, 

 and large herds overwinter on the Arctic Slope (Lent 1966, Hemming 

 1971). Some of the surviving calves and yearlings of these herds may 

 become adjusted to overwintering on the Arctic Slope and add to the 

 nonmigratory component of the northern caribou populations. 



Population Dynamics and Demograpliy 



The number of caribou grazing on the Coastal Plain varies accord- 

 ing to migratory patterns, the number of resident caribou and the stage 

 of their annual reproductive cycle. The number varies seasonally and an- 

 nually in the Prudhoe Bay region. The estimates in Figure 10-17 are 

 based on the total available area, not all of which is utilized by the cari- 

 bou. Estimates based on the seasonal home range can be 5 to 15 times as 

 high and give a good indication of habitat utilization during a season or 

 year (Gaare and Skogland 1975). But the areas visited shift from year to 



FIGURE 10-17. The density of caribou in the 

 Prudhoe Bay region during two years. The solid 

 dots are based on observations of White et at. 

 (1975); the open dots were calculated assuming 

 reproductive performance equivalent to the Por- 

 cupine herd as reported by Calef and Lortie 

 (1973). 



