microtine cycles

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microtine cycles The periodic, density-dependent fluctuations in population size, involving mass migrations, of certain animal species, the best known of which is the Scandinavian lemming (Myodes lemmus), of the rodent subfamily Microtinae, after which the phenomenon is named. An abundance of nutritious food (phosphate being the limiting nutrient for lemmings) causes a rapid increase in numbers; their feeding reduces plant productivity until overcrowding triggers the migration. Cyclical locust migrations can cause catastrophic damage to agricultural crops over large areas.