Weather extremes and insect population dynamics

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In this proposal, I examine the way in which extreme weather and changing climate affect long-term dynamics of the alpine Apollo butterfly, Parnassius smintheus in the Canadian Rocky Mountains. This proposal builds on long-term study of this butterfly (since 1995) examining the effects of rising treeline on loss and increased isolation of these small populations, and of general climate variability. We know that populations have limited dispersal ability, and that their population dynamics are affected most by over-winter weather. Populations decline in years with either extreme warm or extreme cold winters, particularly in years when there is little snow. Because alpine butterflies live in small isolated habitats, have limited dispersal, and are subject to extreme weather events, they serve as an excellent model system for identifying the risks to animal populations in a rapidly changing world. Two MSc students, one PhD student, and I, will identify the mechanisms by which winter temperatures and snowfall affect survival of the over-wintering egg stage, and the degree to which their survival explains variation in annual population growth or decline. We will use experimental planting' of eggs in late summer, and their recovery at intervals through the winter to determine mechanisms by which cold and hot winters affect their survival. We will use high-resolution satellite imagery and ground-based time-lapse photography to quantify snow cover across the meadows generally, and in our egg planting' experimental plots specifically. Results will be extrapolated to the geographic range of this species in an effort to determine the role of winter weather in defining the boundary of their distribution, and the potential for causing shifts in their geographic range. Results will determine whether these populations are at risk to changing climates or that P. smintheus butterflies are sufficiently adaptable via morphology, behaviour or physiology, to mitigate the anticipated warmer, more variable, and less snowy winters in future.