lemmings demystified

Imagine a lemming.

If you, like me, have never seen one of these creatures or bothered to read up on them, you may be picturing a furry, yellow/orange little creature that travels in large groups. And occasionally commit mass suicide. Sound about right? Other myths and misconceptions about lemmings abound. A theory dating back to the 16th century proposes that lemmings fall out of the sky on stormy winter days, only to die suddenly when fresh grass begins to grow in the spring.

This is what a lemming actually looks like! It’s a herbivorous rodent thats population ranges from well north of the Arctic circle down into Norway and other parts of northern Scandinavia. They do not hibernate over winter, but remain remarkably active, burrowing through the snow to search for food. They are notable in the small scientific community that studies wild rodents for their chaotic population fluctuations. When population densities become very high, lemmings may migrate long distances, crossing rivers or even lakes to find new homes. Many will drown or be killed by predators in this process. These perilous journeys are what probably gave rise to the popular myth about lemmings committing mass suicide.

An entirely different theory about lemming population dynamics was proposed by researchers in Greenland and became a hit among ecologists for portraying what may be the simplest predator-prey interaction in the world. These scientists studied the collard lemming in Karup Valley, a high arctic-tundra site located at 72 degrees north latitude. In this harsh environment, lemmings are preyed upon by four species: the stoat, the arctic fox, the snowy owl and the long-tailed skua. The study points to the key role that these predators play in curbing lemming populations. With the exception of the stoat, lemming predator populations are finely attuned to lemming population density. When populations of lemmings reach a certain critical mass, predator density spikes, which in turn leads to a rapid drop in lemming populations. The fox, owl, and skua are all responsible for keeping lemming populations in check in the winter. The stoat, however, hunts lemmings year round. When the other three predators have stopped hunting lemmings towards the end of summer, the influence of stoat predation increases and is ultimately believed to cause lemming population crashes.

Take home message? Mass suicide, though far more dramatic and intriguing, may in fact be a simple coupling of rodent population booms with intense cyclical predation. Sometimes science takes the drama out of life.

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