Your argument is flawed because lemming don't actually jump off of cliffs:
http://www.snopes.com/disney/films/lemmings.htm
"Lemming suicide is fiction. Contrary to popular belief, lemmings do not periodically hurl themselves off of cliffs and into the sea. Cyclical explosions in population do occasionally induce lemmings to attempt to migrate to areas of lesser population density. When such a migration occurs, some lemmings die by falling over cliffs or drowning in lakes or rivers. These deaths are not deliberate "suicide" attempts, however, but accidental deaths resulting from the lemmings' venturing into unfamiliar territories and being crowded and pushed over dangerous ledges. In fact, when the competition for food, space, or mates becomes too intense, lemmings are much more likely to kill each other than to kill themselves.
Disney's White Wilderness was filmed in Alberta, Canada, which is not a native habitat for lemmings and has no outlet to the sea. Lemmings were imported for use in the film, purchased from Inuit children by the filmmakers. The Arctic rodents were placed on a snow-covered turntable and filmed from various angles to produce a "migration" sequence; afterwards, the helpless creatures were transported to a cliff overlooking a river and herded into the water. White Wilderness does not depict an actual lemming migration — at no time are more than a few dozen lemmings ever shown on the screen at once. The entire sequence was faked using a handful of lemmings deceptively photographed to create the illusion of a large herd of migrating creatures.
Nine different photographers spent three years shooting and assembling footage for the various segments that comprise White Wilderness. It is not known whether Disney approved or knew about the activities of James R. Simon, the principal photographer for the lemmings sequence.
Nature documentaries are notoriously difficult to film, as wild animals are not terribly cooperative. Many nature shows and films of this era — including Disney's "True-Life Adventure" movies and TV's Wild Kingdom — staged events to capture exciting footage for their audiences. The sight of a few lemmings mistaking a lake or ocean for a stream and drowning after swimming out too far, or being pushed over a cliff during the frenzied rush of migration, has become the basis of a widespread belief that lemmings commit suicide en masse when their numbers grow too large."