We typically associate butterflies with warm weather, but new modelling shows that climate change resulting in warmer temperatures may harm alpine butterfly populations. 

The Rocky Mountain apollo butterfly, Parnassius smintheus, lives in alpine meadows from New Mexico to the Yukon. It relies on the succulent Sedum lanceolatum for food. This specialist food relationship is featured in a new study published in Global Change Biology by University of Alberta scientists. Lead author Alessandro Filazzola used data from citizen scientists (including iNaturalist and eButterfly) to track both the butterfly and the plant in North America. He then modelled different climate scenarios to figure out how climate change would affect the range of P. smintheus compared to generalist alpine butterfly species that are less picky eaters. Both wetter and drier climate futures were included in the modelling.

Filazzola says that a lot of climate modelling can be too one-dimensional, focusing on one species at a time. “If we only look at the butterfly in isolation, it’s always good news.” 

In butterfly-only models, the butterfly’s range expanded with climate change, whether the climate got wetter or drier. “But then once we introduce the host plant into the mix,” says Filazzola, “the story changes.”

In scenarios where the west coast climate gets drier, the inclusion of Sedum resulted in a net loss in the butterfly’s distribution area — whereas the climate-only model had suggested an increase. Compared to more generalist butterfly species, P. smintheus showed the largest loss in suitable habitat. In scenarios where the west coast gets wetter, the climate-only model projected a net increase in P. smintheus’ distribution, but with Sedum included the increase was much smaller. While it’s hard for climate models to predict precipitation changes, Filazzola says there’s a lot of support for the idea that the west coast will get drier — bad news for the butterfly.

The new study is part of a longstanding butterfly project near Barrier Lake in Alberta’s Kananaskis Country, started by Jens Roland in the 1990s. Butterflies are important alpine pollinators and their caterpillars are a valuable food source. Despite their delicate appearance, butterflies are at home in the tough environment. But as the climate warms, food availability isn’t their only problem. Over the decades, the project’s researchers have contributed to our knowledge of the threats faced by alpine butterflies. 

Snow is important for alpine butterflies, forming an insulating layer over their eggs in the winter. If there’s not enough snow in the mountains, cold exposure will kill the eggs before spring. The encroaching treeline is another threat. As the climate warms and high-altitude meadows turn into shrub or forest, butterflies have nowhere to go. For an insect the size of a few loonies, the next mountaintop is often out of reach.

While the best way to help alpine butterflies is to stop climate change, Filazzola says his research could be extended to help us understand how to mitigate climate impacts on other species. The more species that can be incorporated into models, the better our ability to predict the future, equipping us to make more informed decisions on how to save species beyond butterflies.