

'30' 



Stac an An 

 SAINT KILDA Stacl 



57° 50' 



Joe LeMonnier 



30 Natural History 3/94 



and voles. Lemmings, which are larger, 

 sometimes show cycles of three to four 

 years. Muskrats may peak every seven 

 years and snowshoe hares at nine years. 

 Peterson's group suggested that the cycle 

 length depends on the rate at which the 

 population can expand, which, in turn, de- 

 pends on generation length. Because large 

 mammals mature more slowly and breed 

 less frequently than small ones, they have 

 longer generation times and lower rates of 

 increase and therefore may show longer 

 cycles. Using the known relationship be- 

 tween body size and cycle periodicity in 

 smaller animals, Peterson scaled up the 

 figures and predicted that cycles might 

 occur every thirty years in moose and 

 every seventy years in elephants. We do 

 not yet have data spanning many decades. 



