Demography of snowshoe hares in relation to regional climate variability during a 10-year population cycle in interior Alaska

We monitored populations of snowshoe hares (Lepus americanus, Erxleben) in interior Alaska for 10 years from 1999 to 2008. During this period, fall densities of hares fluctuated approximately 14-fold. High population growth rates over summer (λ = 1.83–8.00) were followed by large population declines over winter (λ = 0.16–0.82). Young-of-the-year hares tended to gain mass over winter, while adult hares tended to loose body mass. The average mass of adult hares was significantly lower during the low phase of the cycle compared with when hares were abundant. Overwinter survival of juveniles relative to adults decreased strongly as a function of the frequency of snowfall events. However, effects of temperature and precipitation on hare demography were season dependent and appear to act as modifiers of the primary controls over population dynamics (predation and food) rather than as direct sources of mortality. The rapid changes in green-up and snow-up in interior Alaska may affect forage conditions as well as the timing of molt in snowshoe hares. The strength of these interactions may increase in importance if the asynchrony of environmental seasonality and life history traits of snowshoe hares becomes more pronounced as the climate continues to change.