Snowshoe hare (Lepus americanus) and lynx (Lynx canadensis) populations show 9- to 11-year cycles throughout the boreal coniferous forests of Canada and Alaska. Lynx cycles, recorded in Hudson Bay trapping records covering many decades, have been analyzed by population ecologists interested in understanding the mechanisms underlying the cycle (Royama 1992, Ranta et al. 1997). Long-term records of hare cycles are less common but there have been two major field programs that have measured demographic changes over at least one full cycle. This includes the work based at Rochester, Alberta by Lloyd Keith and co-workers (Keith et al. 1984, Keith 1990) and our work based at Kluane, Yukon (Krebs et al. 1986, Sinclair et al. 1988, Krebs et al. 1995). These field studies have established the demographic mechanisms that drive changes in hare numbers and have tested mechanistic hypotheses about factors that stop population increase and cause the hare population decline (Keith 1990, Krebs et al. 2001b).

It is clear that the lynx and hare are tightly linked (Royama 1992, Stenseth et al. 1998). Lynx show strong functional and numerical responses to changes in hare density (Keith et al. 1977, O'Donoghue et al. 1998). In turn, the dominant proximate cause of hare mortality is predation (Keith et al. 1984, Boutin et al. 1986) with lynx being one of a suite of hare predators.