Canadian alpine butterflies deserve better monitoring
Rocky Mountain parnassian, also known as Rocky Mountain apollo, (Parnassius smintheus) female at Plateau Mt., Alberta. 2018. Photo. Z. MacDonald.
Alpine butterflies are easy to love for their exuberant animation across scree slopes and mountain meadows. While most of us only encounter alpine butterflies on sunny, summer days, they are far from being limited by such agreeable conditions. Their fragile butterfly bodies hide tenacious adaptabilities that have allowed them to persist in extreme environments for millennia, while glaciers ebb and flow around them, with genetic changes slowly being recorded in their DNA and the patterning of their wings. In our part of the world, alpine butterflies range in size from the six-centimetre wingspan of parnassians (Figure 1), with a creamy background highlighted by bright red eyespots, to just two centimetres of patterned gray and white in grizzled skippers. Populations inhabiting different regions, ranges, or even single isolated mountains are often given different names due to slight differences in genetics, appearance, and behaviour. Each has scientific value, with much to tell us about how environmental changes are affecting alpine habitats. Indeed, with warming temperatures around the world, many alpine butterflies are moving both northward and up mountain slopes, while others are simply disappearing. Such changes can only be detected by monitoring these alpine gems before they are literally swept off a cliff, with no way to return.
Most of the forty-odd species of alpine butterflies that occur in Canada may be found somewhere in the mountains of Alberta, British Columbia, and the Yukon. Many, like Edith’s checkerspot (Figure 2), are restricted to the southern reaches of Alberta and B.C., having survived south of the ice sheets during the last glacial maximum, some 30,000 to 11,000 years ago.[1] Other species, like Eversmann’s parnassian, are restricted to the northern half of B.C. and the Yukon, having braved the last glacial cycle in the nearby Beringian refugium. Most butterflies with Beringian or northern arctic distributions, like Ross’s alpine, have larvae that feed on grasses and sedges, which suggests that these regions had more steppe-like habitats during the last glaciation, rather than the wet tundra habitats observed today. In these ways, studying the unique distributions and life histories of alpine butterflies provide many insights into the nature of ancient alpine environments.
Edith’s checkerspot (Euphydryas editha) on yarrow flower at Plateau Mt., Alberta. 2018. Photo. Z. MacDonald
Alpine butterflies are also sensitive indicators of recent and ongoing environmental change. We already knew in the 1990s that Edith’s checkerspot has been shifting its range toward the north into Canada.[2] Since then, considerable evidence has shown that other alpine species are doing the same.[3] But each species has its own particularities. The Rocky Mountain parnassian is a well-studied alpine butterfly that frequents dry alpine slopes where stonecrop, its larval food plant, is found. In the front ranges of the Rocky Mountains of southern Alberta, some twenty years of monitoring have shown that extreme temperatures and lack of snow cover in early winter, when the butterfly is in the egg stage, are better predictors of population numbers than any general climate index.[4] Much less is known about the environmental factors that affect this butterfly throughout B.C. and the Yukon, where three other subspecies are recognized. Many lepidopterists (those who study or collect butterflies and moths), including ourselves, are trying to fill these knowledge gaps. And yet, this species is but one of many that illustrate the complex interplay of past and current factors that structure alpine butterfly communities.
Many human influences can affect butterfly distributions, some more obvious than others. In combination with global climate change, fire suppression has resulted in visible encroachment of trees in alpine meadows across Alberta and B.C. (Figure 3). Rising treelines don’t just mean less habitat, but also diminish the number of butterflies flying between mountains. Such dispersal events are needed to rescue isolated and dwindling populations or boost their genetic diversity. Factors like changing snowpack, or the death of high-elevation pines due to mountain pine beetles or introduced blister rust,[5] can also have profound influences on mountain hydrology and the diversity of nectar sources and larval food plants. Even seemingly distant threats like pesticides can condense and become more concentrated in the cooler temperatures of alpine and arctic habitats.[6] It is clear that many human-mediated factors influence alpine butterflies, but the inaccessible and fragmented nature of butterfly habitats has left much to be discovered.
View to the southeast from Mt. Faith, near Christina Lake, B.C. 2019. Photo. W. Sperling.
Fortunately, the attractive nature of alpine butterflies may yet contribute to their use as valuable sentinels of alpine habitats. With ever-growing interest in backcountry exploration, monitoring of alpine butterflies can be greatly aided by taking a few minutes to snap and upload a good photo, or even packing a small net to bring back samples for genetic work. We already have accessible databases of historical museum specimens for Canada.[7] Now, new citizen-science observations and photos are easily compiled on digital repositories like iNaturalist (www.inaturalist.org) or eButterfly (www.e-butterfly.org). Information for alpine and arctic butterflies is still sparse, and yet they are likely to be among the best indictors we have of the profound changes that their habitats are beginning to experience.
Felix Sperling is a Professor of Biological Sciences and Curator of the Strickland Museum of Entomology at the University of Alberta.
William Sperling is a Registered Professional Forester based in Grand Forks, B.C.
Zac MacDonald is a PhD candidate in the Department of Renewable Resources, University of Alberta. His research focuses on the landscape ecology and population genetics of boreal and alpine butterflies.
References
1. Guppy, C.S., Shepard, J.H. Butterflies of British Columbia (UBC Press, 2001).
2. Parmesan, C. Climate and species’ range. Nature 382, 765-766 (1996).
3. Lewthwaite, J.M.M. et al. Canadian butterfly climate debt is significant and correlated with range size. Ecography 41, 2005-2015 (2018).
4. Roland, J., Matter, S.F. Pivotal effect of early-winter temperatures and snowfall on population growth of alpine Parnassius smintheus butterflies. Ecological Monographs 86, 412-428 (2016).
5. Shepherd, B. et al. Ten years of monitoring illustrates a cascade of effects of white pine blister rust and focuses whitebark pine restoration in the Canadian Rocky and Columbia Mountains. Forests 9, 138 (2018).
6. Villa, S. et al. Historical trends of organochlorine pesticides in an alpine glacier. Journal of Atmospheric Chemistry 46, 295–311(2003).
7. See Canadensys (https://community.canadensys.net/)