Never Cry Wolf (the movie), one of the most enjoyable cinematic experiences of my life, has a bit about lemmings.
A young biologist sent to northern Canada to study wolves observes a canine feasting upon migrating lemmings and decides to perform an experiment. Can a large carnivore (yes, I know they are omnivores, but I recall the book and movie said "carnivore") subsist on only lemmings? There's a bit more to it than that, but I won't spoil the WHOLE act.