Abstract
Introduction. The livestock industry is familiar with the wide and economically significant variations in reproductive output of domestic animals that result from good and poor environmental conditions. The cyclical abundance and scarcity of species in nature in response to favorable and unfavorable environment have long aroused scientific interest and speculation concerning the specific causes and mechanisms that are involved. Julian Huxley (1927) has cited some of the outstanding examples of these periodic outbursts of generative energy. The lemming of Scandinavia was cited as the best known example of cyclical abundance. This animal of the mountains of Southern Scandinavia becomes so abundant every few years that the young animals set off on migrations in all directions in enormous numbers. If they come to the sea, they enter the water and swim out until they drown, the coast becoming strewn with their corpses. Copyright © . .

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