338 



G. O. Batzli et al. 



have reached substantial numbers only once in the last 20 years, 27 ha"' 

 in 1971 (Figure 10-2). No other vertebrate herbivores regularly inhabit 

 the Barrow peninsula, but a few caribou (Rangifer tarandus) and ptar- 

 migan {Lagopus lagopus) visit occasionally. A discussion of herbivory 

 can therefore center on a single species: the brown lemming. 



Population Dynamics and Demography 



Changes in the lemming population have been monitored for 20 

 summers, from 1955 to 1974. During that time densities have fluctuated 

 between peaks of up to 225 trappable lemmings ha"' and lows of 0.02 

 ha"', with three to six years elapsing between peaks (Figure 10-2). 

 Although reliable estimates of population size were not made before 

 1955, high densities were also observed in 1946, 1949 and 1953 (Pitelka 

 1957b). These fluctuations have traditionally been called cycles, largely 

 because of their great amplitude (3 or more orders of magnitude), even 

 though all aspects of successive cycles are not alike. 



240 



200 



160 



,; 120 



o 



80 



40 



l\ 



• Lemmus 

 oDicrostonyx 



; 



?'Lj 





? 



it 



I', 



■-I — ^ i#^ 



V 



OO 00 



^^. 



551 



1601 



1651 



1701 



174 



Year 



FIGURE 10-2. Estimated lemming densities averaged for all 

 habitats in the coastal tundra at Barrow for a 20-year period. 

 The question marks indicate numbers based upon observations 

 other than trapping. 



