Workshop on Predation
The Lynx and the Snowshoe Hare: References and Background Information

In 1942, Elton and Nicholson analyzed the apparently natural fluctuations of Lynx populations in eastern Canada by cataloging the numbers of pelts purchased from trappers by the Hudson Bay Company over more than a hundred year span. The authors proposed that the population densities of Snowshoe Hare and Lynx appeared not only to fluctuate over time, but to be coupled, with Lynx population declines shortly following similar decline in Snowshoe Hare populations. For a long time after the paper's publication, the cyclical, paired fluctuations were interpreted as a stable predator-prey relationship: as prey numbers declined, predators began to starve and die, thus allowing a resurgence of the prey population.

However, later analyses of the data and critical review of the original paper revealed different possibilities for those population fluctuations. Some of the more interesting reviews can be viewed here. Read and consider their ideas before you do your workshop.

  • Finerty, J. Patrick. 1979. Cycles in Canadian Lynx. The American Naturalist,
  • Gilpin, Michael E. 1973. Do Hares Eat Lynx? The American Naturalist, Vol. 107, No. 957. pp. 727-730
  • Weinstein, Martin S. 1977. Hares, Lynx, and Trappers. The American Naturalist, Vol. 111, No. 980, pp. 806-808

    Still later, other authors provided other possible reasons for the coupled fluctuations, including Keith (1983), who argued that it was not predation, but a shortage of suitable winter forage that caused the hares' population decline. Keith showed that heavily browsed plants produce high levels of alkaloids and other aversive compounds that may make them toxic or highly unpalatable to the hares. While he agreed that the Lynx population depended on the hares, he proposed that it was food supply that affected the populations of both predator and prey--and not predation precipitating decline in the hares.

    As add as it may sound, Moran (1949), and later reviewed by Ranta, et al. (1997) suggested that the population fluctuations were correlated with sunspot activity. In any case, Moran's hypothesis was challenged by Ranta (1997), who noted that no other cyclical patterns similar to the hare/lynx pattern were noted elsewhere on earth in relation to sunspot activity, which would be expected if sunspots were truly the cause.

    The controversy rages on. Will you be the next contributor?