Some Essential Features of Short-Term Population Fluctuation

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Abstract
Population fluctuations in northern mammals and birds is established as being a regular 3- to 4-year cycle. In addition, about every third peak is higher than the others (ca. 10-year fluctuation). If the fluctuation diverges from this pattern either by having no peak in some local populations in a general peak year or by falling at a differing point of time, the next peak as a rule will immediately return to the synchronic fluctuation. Southwards the force of the fluctuation weakens and the fluctuation itself at the same time grows more irregular. A striking feature is the notable synchronism of fluctuations in species with very varying size, life span, reproduction and ecology, as well as in very different regions. The fluctuation occurs in its most typical form (dominant) in herbivores whose principal nutriment remains constant in quantity from one year to another. Tetra-onids generally reach the peak first and small rodent 0-1 year after this (Tables 3-5). The biology of reproduction of the tetraonid populations gives reason to assume that the decline already has been determined before the egg-laying stage of the low year. The fluctuation curves for predators and for seed-eating herbivores must be regarded as special cases on their own. The same applies to fluctuations in the populations of prey, caused by predators, and fluctuations in the more southern regions. Attention is paid to the deficiencies of the fluctuation series available and their unspecific nature as well as to the necessity of data being collected using uniform methods and covering various species and various areas.

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