If lemming populations around Prudhoe Bay 
always remain relatively low, perhaps the most 
important factor may be the presence and the 
movement during the summer of caribou in the 
habitat of the lemming. Although they do not 
give any quantitative data from their observa- 
tions of collared lemming communities on the 
North Slope of Alaska, Bee and Hall (1956) 
claim that in certain areas the caribou controls 
the lemming population. At Barrow, where high 
populations of lemmings occur regularly, cari- 
bou are not an important element in the tundra 
ecosystem. At Prudhoe Bay, caribou annually 
migrate into the area in June, graze the area 
until September, and migrate out again to win- 
tering grounds (White et al., this volume). In 
1972, between 30 June and 30 July, at least 
several thousand caribou moved across the area 
near Prudhoe Bay which included the live trap- 
ping grid sites in the present study (White et al., 
this volume). On 10 July 1972, 1,600 caribou 
were seen slowly traversing the area which in- 
cluded our lemming trapping grids, during a 
141 
period of several hours, grazing intermittently as 
they moved. MacLean (pers. comm.) reported 
that the passage of large numbers of caribou, as 
was seen at Prudhoe Bay in mid-July 1970, 
resulted in heavy grazing pressure on the vegeta- 
tion as well as severe physical disturbance from 
trampling. It is reasonable to assume that the 
impact of these large herbivores on the local 
lemming populations through competition for 
food and space and through physical disturbance 
or destruction of habitat may be great. However, 
this remains conjecture until clarification by 
further studies. 
In addition to the probable effect of caribou 
on depressing lemming population numbers, cer- 
tain predators may play a significant role in 
affecting lemming numbers (Pitelka 1957, Maher 
1970). No quantitative data are available for 
avian predators (Norton et al., this volume) or 
for mustelid predators at Prudhoe Bay. The 
arctic fox (Alopex lagopus) may prey upon a 
significant portion of the available lemmings 
(Underwood, this volume). During the winter of 
Table 3 
Density estimates for collared lemmings on three grid areas near 
Prudhoe Bay. Numbers in parentheses are the actual number captured on grid area. 
June July August 
1971 1971 1971 
Grid P* (low relief 0 0 0 
polygons and tussocks) 
Grid Q* (low relief 2.2(2) 0 0 
tussocks) 
Grid S* (shallow pingo 0 0 0 
and surrounding area of 
very low relief tussocks) 
+Numbers ha | 
mid-June early July late July mid-August 
1972 1972 1972 no72 
7.4(8) 10.2(7) 3.3(2) 0 
4.3(5) 6.6(5) 5.3(4) 0 
1.6(1) 0 3.3(2) 1.6(1) 
“Grid area = 0.25 ha; effective trapping area estimated as follows to compensate for lemming movements (re: Brooks 
and Banks 1971). See methods section for further explanation. 
adult and subadult females probably without homesite 
adult and subadult pregnant females probably with homesite; and juvenile females 
subadult and juvenile males 
adult males 
2.89 ha 
(60 m strip) 
0.61 ha 
(14 m strip) 
0.61 ha 
(14 m strip) 
i 10.0 ha 
(134 m strip) 
+Values are estimated minimum number of animals present per effective trapping area. 
