Friday, August 16, 2013

Lemming diet

Lemmings became the subject of a popular misconception that they commit mass suicide when they migrate. However, it is not a mass suicide, but the result of their migratory behavior. Some species of the small rodents (e.g. the Norwegian lemming, Lemmus lemmus) may migrate in very large groups when population density becomes too great. Lemmings can swim and may choose to cross a body of water in search of a new habitat. In such cases, many lemmings may drown if the body of water is so wide as to stretch their physical capability to the limit. This fact, combined with unexplained fluctuations in the population of Norwegian lemmings, gave rise to the misconception. Lemmus lemmus can reproduce so quickly that population fluctuations become chaotic, rather than following linear growth to a carrying capacity or regular oscillations. It is unknown why lemming populations fluctuate with such great variance on average every four years. Only recently new evidence suggested that populations of lemming predators, particularly the stoat (Mustela erminea), may be more closely involved in changing the lemming population. 

As lemmings function as the main trophic link between vegetation and predators in most tundra ecosystems, their high amplitude population density cycles often have a major impact on tundra food webs. A new study now aimed to correctly evaluate the effect of lemmings on vegetation by identifying what they feed on in the wild:
Lemmings are key herbivores in many arctic food webs, and their population dynamics have major impacts on the functioning of tundra systems. However, current knowledge of lemming diet is limited, hampering evaluation of lemming–vegetation interactions. This lack of knowledge is mainly due to methodological challenges, as previously used microhistological methods result in large proportions of poorly resolved plant taxa. We analyzed diets of Norwegian lemmings (Lemmus lemmus) in three different habitats using a new method, DNA metabarcoding of stomach contents. To achieve detailed information on ingested vascular plants, bryophytes, and fungi, we amplified short fragments of chloroplast DNA (for plants; P6 loop of the trnL intron) and nuclear ribosomal DNA (for fungi; ITS1-region). Our results revealed that lemming diets were dominated by grasses, mainly Avenella flexuosa, and mosses, mainly Dicranum spp., but that a variety of other food items were also eaten. Vascular plant composition of the diets differed between heath, meadow, and wetland habitats, whereas bryophyte composition did not. Also, a variety of fungal taxa were retrieved, but as most of the identified taxa belong to micromycetes, they were unlikely to be consumed as food. The role of fungi in the diet of lemmings remains to be investigated. We suggest that there may be substantial variation between habitats and regions in lemming diet.

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