Norway lemmings are part of the tundra food web.  They are both primary and secondary consumers.  Predators that feed on lemmings are the Arctic fox, snowy owl, and certain hawk species.  Norway lemming compete with reindeer for nutrients.  When the reindeer population becomes to large, the lemming population decreases.  Because of their large population fluctuations, Norway lemmings also undergo intraspecific competition for resources.