The Norway lemming, a small Arctic rodent, is a recognizable symbol of its challenging yet vibrant environment. It inhabits tundra and mountain regions, playing a unique role in the ecological dynamics of its harsh habitat. Its significance extends beyond its small size, impacting the intricate web of life.
Distinctive Characteristics and Habitat
The Norway lemming (Lemmus lemmus) is a compact rodent, weighing 20 to 130 grams and measuring 8 to 17.5 centimeters. Its robust body is covered in thick, black, brown, and golden-yellow fur that remains consistent year-round. Short limbs and large, flattened claws on their front paws assist them in tunneling through snow.
These lemmings thrive in the tundra and alpine regions of Fennoscandia, which includes Norway, Sweden, Finland, and northwestern Russia. They inhabit moist habitats such as bogs, marshes, fells, and heathland with dwarf shrubs. During winter, they create insulated spaces and tunnel systems beneath the snow, providing warmth, shelter, food access, and protection from predators.
Their diet consists primarily of Arctic flora, including sedges, grasses, mosses, lichens, and sometimes berries, roots, and shoots. Norway lemmings are active day and night, alternating foraging with rest. They are known for their solitary and aggressive nature, particularly when territories become overcrowded. They may exhibit vocalizations or charge towards perceived threats, including predators or humans.
Understanding Population Cycles
Norway lemmings are known for their remarkable population cycles, where numbers dramatically increase before sharp declines, typically every three to five years. These mass movements are not acts of intentional self-harm or “mass suicide.”
The misconception of mass suicide was amplified by a staged scene in the 1958 Walt Disney documentary White Wilderness, depicting lemmings herded off a cliff. When populations reach high densities, lemmings disperse widely for new territories, food, and shelter. These dispersal events can lead to accidental deaths, such as falling off cliffs or drowning, but are unintended consequences of their migratory behavior.
Several factors contribute to these cyclical fluctuations. Food availability is a factor, as dense populations can overgraze vegetation, leading to resource scarcity. Predator populations also influence lemming numbers; as lemming populations grow, predator numbers often increase, leading to a decline in lemming populations. Disease can also contribute to population crashes during high density periods. Warmer winters with less consistent snow cover can reduce insulated spaces lemmings use for foraging and protection, impacting their winter survival and subsequent population booms.
Role in the Ecosystem
The Norway lemming is a primary food source for various Arctic predators, including Arctic foxes, stoats, snowy owls, rough-legged buzzards, and skuas, all relying heavily on lemmings. Fluctuations in lemming populations directly impact the breeding success and survival of these predators. For instance, abundant lemming years often lead to increased breeding and larger clutch sizes for raptors like snowy owls.
When lemming populations are low, predators may switch to alternative prey, such as ground-nesting birds like ptarmigans and waders, which can then decline in numbers. Beyond predation, lemmings influence vegetation through grazing. During population peaks, lemming densities can be high, with up to 330 lemmings per hectare, leading to consumption of grasses, mosses, and sedges. This intense grazing can impact the landscape and even delay vegetation recovery for several years. Additionally, lemming droppings can fertilize plants, indirectly benefiting other herbivores like reindeer and Arctic hares.