Productivity and Populations 321 



character of sunspot action. The fact that some grouse populations 

 are high when the general trend in an area is low does not fit the 

 pattern. And, except for its effect on animals through weather con- 

 ditions, the mechanics of sunspot effect on animal numbers leaves 

 a lot of explaining to be done. Nevertheless, there is enough meat 

 to the theory so that it cannot be entirely disregarded. Affecting 

 weather as they do, they must exert some effect on animal Iffe. The 

 possibility that the retarding effect of ultraviolet rays on plant 

 growth may affect the food supply of certain herbivores, thus in 

 effect causing a type of starvation, has yet to be proved or disproved. 

 It may have merit. 



11. Numerous Other Suggested Causes of Cycles Warrant Less 

 Consideration. 



The possibility that inbreeding may result in degeneration of the 

 stock is adequately taken care of by the fall shuffle of populations 

 which prevent inbreeding. Man's hunting is easily ruled out since 

 the cycle is effective in wilderness areas where no hunting takes 

 place. In fact, there is some indication that the periodic decimations 

 are more pronounced in extensive wilderness range than in broken- 

 up range in man-inhabited country. 



Lack of food can hardly be considered seriously,^ except as al- 

 ready noted: (1) quality of food may conceivably be affected by 

 sunspot action; ( 2 ) adverse weather may affect insect food supply 

 of yoimg chicks. Criddle (1930) indicates a correlation between 

 cycles in grasshoppers and cycles in sharp-tail grouse, and suggests 

 there may be a correlation also with ruffed grouse cycles. However, 

 this seems remote when we consider the minor importance of grass- 

 hoppers in the ruffed grouse diet. Shelter likewise cannot be corre- 

 lated with abnormal die-off since these decimations seem to take 

 place in all types of cover and range. There is no evidence from the 



^ Elton (1942) makes a good case for food scarcity being connected with tlie pre- 

 cipitation of cyclic decline of lemmings and voles in the north. "Lemmings must make 

 very great inroads upon the vegetation, which sets definite limits to the amount of 

 their increase and to their local distribution on the timdra. ... As the cycle in 

 population mounts steadily for several years, it reaches a breaking point and crashes. 

 The danger signals are not long delayed in a community dependent upon the ex- 

 iguous supplies of a northern land. Vegetation is denuded of the reserves built up in 

 ^e previous time of lemming scarcity." Kenneth Doutt of the Carnegie Musetmi 

 says lemmings were abundant in Labrador when he arri\'ed there in Winter 1945. 

 By June most had died. Their remains were everywhere, and many were found dying. 

 There was plenty of food available. He believes lack of food could not have caused 

 the losses. 



