These cycles seem to be driven by inter-dependent predator-prey relationships.

• The hare population size grows,
• providing more food for the lynx,
• which then reproduce at a higher rate,
• causing them to eat great numbers of the hares,
• thereby reducing the hare population (and the lynx's food source),
• causing the lynx population to crash,
• enabling the hare population to grow again.

Note each cycle endures a bottleneck, possibly leading to extinction.