346 G. O. Batzli et al. 



TABLE 10-2 Home Ranges (Mean ±1 SE in 

 Hectares) of Lemmings on 

 Low-centered Polygons 



1972 1973 



Males 1.33±0.28 (12) 0.88 ±0.28 (13) 

 Females 0.68 ±0.37 (6) 0.41 ±0.31 (11) 



Note: Sample sizes are given in parentheses. 

 Source: Banks et al. (1975). 



to have smaller home ranges than males (Table 10-2), but the variability 

 is such that differences were not statistically significant. Differences also 

 occurred from year to year, but again variability was high. Analysis of 

 the frequency of movements of 5 m or more indicated that males moved 

 more than females and that more movement occurred in 1972 than in 

 1973 (ANOVA,/7< 0.01). 



The greater movement of males probably results from the mating 

 system of lemmings, viz. promiscuous polygamy. Males can increase 

 their fitness by touring the habitat in search of females, whereas females 

 restrict their movements, usually moving between foraging sites and nest- 

 ing burrows. A combination of increased energy requirements and vul- 

 nerability to predation when moving probably limits male movements. 

 The greater movement of lemmings in 1972 than in 1973 was correlated 

 with higher population density (Table 10-1), hence greater social interac- 

 tion, and with a lower rate of predation in 1972. 



Summer activity in polygonized terrain takes place primarily in the 

 troughs. Lemming burrows are concentrated on the sides of troughs 

 above the water line or on the sides of high-centered polygons. Summer 

 nests are usually located in these burrows or under elevated patches of 

 moss {Sphagnum spp.). Runways follow troughs, particularly the frost 

 cracks associated with them. Foraging activity is concentrated near the 

 burrows and along the sides of runways. About 95 to 10097o of graminoid 

 shoots in the immediate vicinity of burrows are repeatedly clipped while 

 the burrow remains occupied. Away from the burrows, clipping is 

 patchy, and intensity decreases as distance from the runways increases. 

 Cheslak (pers. comm.) found only from to 30% of shoots clipped at a 

 distance of 0.5 m from runways when lemming densities were moderate, 

 about 10 ha"' . Maps of the locations of radio-tagged lemmings show pat- 

 terns that match the patterns of polygon troughs (Banks, pers. comm.). 

 In nonpolygonized terrain the association with microtopographic 

 features is not so clear, and lemming activity appears to be located in 

 more randomly distributed patches, but, again, clipping is concentrated 

 near runways. 



