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Grand Teton National Park Report

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Multiannual fluctuations in population density ("cycles") have been known since antiquity (Elton 1942). Numerous hypotheses have been proposed to explain this phenomenon (for reviews see Krebs and Myers 1974, Finerty 1980, Taitt and Kreh; 1985). However, none of these hypotheses, alone or in combination, can either explain the causality of cycles or predict their dynamics. The ultimate objectives of this long-term study are to answer two questions: (1) What causes multiannual fluctuations in the population density of microtine rodents?; and (2) How can cycles be predicted? The proximate objectives are to determine to what extent environmental variables - acting through reproductive responses of Microtus montanus- contribute to the population density cycles of these rodents.