Our recent study, published in Communications Biology, investigates the distribution of 131 butterfly species across Sweden and Finland over the past 120 years, revealing a fascinating interaction between climate, land use, and species traits.
These computer-generated illustrations present an artistic representation of butterflies on the move. The depicted species are not real but were created for illustrative purposes to emphasize the movement of butterflies due to environmental changes.
Because of their sensitivity to environmental changes, butterflies are well suited for studying how biodiversity is influenced by climate change. As our planet warms, we have noticed that these beautiful insects have gradually altered their range, expanding northwards. In our research, we discovered an astonishing 64% increase in average provincial species richness, expanding from 46 to 70 species per province.
But it's not as simple as butterflies just following the heat. Their colonizations and range shifts do not solely match how temperatures have changed over time in different parts of the study area. Instead, whether and how much butterflies have modified their ranges is influenced by various factors in addition to temperature shifts, including land use changes and species traits, such as ecological adaptability and inter-species interactions. Thus, butterflies paint a comprehensive picture of the ecological consequences of climate change – a complex interplay between temperature, geography, and biology.
But why do butterflies move? Our findings suggest that their range expansions are part of a broader ecological process. As the climate warms, butterflies may move in search for habitats that meet their specific requirements regarding temperature conditions, food sources, and more. If they encounter habitats where conditions are unsuitable, for instance if key food sources are not available, they probably continue their journey. Therefore, it's not only the temperature that guides these movements but also a mismatch between environmental conditions and species preferences.
What does this pattern of butterfly movement mean? Their journeys and the changes in species richness are reflective of broader ecological shifts. As butterflies flutter to new territories, they alter species composition in the local ecosystems. They act as pollinators, prey for other species, and contribute to biodiversity. Therefore, the movement and rearrangement of butterfly communities can have potentially profound impacts on ecosystem functioning.
Example of an expanding butterfly in Northern Europe. The adult Scarce Tortoiseshell, or Yellow-legged Tortoiseshell (Nymphalis xanthomelas), showcases its beautiful wings (left), while a caterpillar of the same species feeds on a Willow (Salix species) leaf (right). These images depict the life cycle stages of this species, emphasizing its ecological role as a food resource for birds and a herbivore. Photo credit: Markus Franzén.
Butterflies' response to climate change is a story of resilience, adaptation, and the intertwined nature of ecological systems. Their journey serves as a stark reminder that climate change isn't just about rising temperatures but also about the complex transformations of ecosystems, including modifications of land use. It calls for an understanding and conservation effort considering a broad ecological perspective, including climate, land use, and species traits.
As we continue to face the realities of climate change, our study underscores the importance of comprehensive ecological research. In their beautiful, fluttering way, butterflies remind us of the intricate dance between all life and the environment we share. Our research revealed that this phenomenon was not only influenced by external conditions and specific species traits but also by ecological filtering and species interactions. These latter factors were instrumental in determining the potential for species to establish new populations and expand their range.
Pictured here are two different seasonal morphs of the expanding Map Butterfly (Araschnia levana). The spring generation is distinctly orange (left), while the summer generation features striking black and white markings (right), demonstrating the species' role as a pollinator. Another example of an expanding butterfly in Northern Europe. Photo credit: Markus Franzén.
One of the key findings was that the colonization rate decreased with the original species richness in each province and period. Specifically, the southern, most species-rich provinces have seen fewer new species. This could be because Finland and Sweden are bordered by sea in the south, effectively limiting colonization by species with weaker dispersal capabilities. This pattern might also point to a role of species interactions.
Interestingly, the average trait value distributions differed between species in original communities and species that colonized new provinces. This supports our conclusion that range expansions were associated with species traits. Moreover, the within-group variability of trait values was generally larger in colonizing species than in the receiving community. This could mean that species with rare or unique trait value combinations had a higher probability of being recruited into the community, possibly due to rare traits and preferences increasing the likelihood of filling available but previously unoccupied niches.
However, this was not a uniform pattern across all provinces. In some northern provinces, the colonizing species were actually less variable than the original communities. This might be due to the original communities comprising cold-tolerant generalist species. With climate change altering the distribution of resources, these areas are now seeing colonization by more specialized, thermophilic species. On the other hand, the more species-rich provinces in the
south-central regions may have been more accessible for species relying on rare or unique resources not already utilized by members of the original community.
The Pallas' Fritillary (Argynnis laodice) represents a species known for its expanding ranges in response to climate change and altered land use. Photo credit: Markus Franzén.
By looking at the intricate dance between species, their traits, and the changing environment, we can see that butterflies' responses to climate change are far from straightforward. They give us a valuable lesson on the complexity of ecological systems, demonstrating the importance of understanding and accounting for a wide array of ecological factors when addressing climate change impacts.
Now, as you see butterflies fluttering in your garden, remember they're not just simple creatures but key players in our ecosystems. Their journey gives us insights into the impacts of climate change, helping us prepare for and mitigate these changes effectively.
Link to the paper:
Sunde, J., Franzén, M., Betzholtz, PE. et al. Century-long butterfly range expansions in northern Europe depend on climate, land use and species traits. Commun Biol 6, 601 (2023). https://doi.org/10.1038/s42003-023-04967-z