Snow cover is an extremely variable but critical component of alpine environments. We use long term population data on multiple small populations of the alpine butterfly Parnassius smintheus, combined with high-resolution satellite imagery of meadows, to show a strong link between fine-scale spatial and temporal variation in early-winter snow cover and annual change in butterfly population size, accounting for up to 80 percent of the variation in annual population change. Snow cover in early winter for each meadow is the best predictor of annual adult population change, despite being estimated for a relatively short time-window in late November. We identify a means by which subpopulation response to a local, short-term weather variable can be assessed over a large spatial extent, but also at a resolution relevant to the biology and local dynamics of this alpine species.

List of variables:

meadow          identifying letter for the meadow

year                 year (t) in which population is estimated and weather variables are recorded.

Rt                    annual rate of population growth in a meadow from year t to year t+1

Nt                    population size of the meadow in year t

logNt               log₁₀ of population size (plus 0.5)* of the meadow in year t

percent            percent snow cover in meadow from satellite imagery in November

size                  size of meadow in hectares

meant              mean daily temperature (°C) for the month of November in year t

extmint           extreme minimum temperature (°C) in November of year t

extmaxt           extreme maximum temperature (°C) in November of year t

*Note: 0.5 was added to population size (Nt) prior to taking the log.