The study is the largest compilation ever made of how butterfly distribution ranges have changed over time. Researchers from a large number of countries have worked together to collect and analyse the data. The results are clear.
“Butterflies are changing their distribution ranges all over the world,” says Lars Pettersson, Associate Professor of Animal Ecology at Lund University and one of the study’s authors.
Climate change and extreme weather events are considered the main causes of changes in butterfly occurrence. Lars Pettersson explains that butterflies can provide valuable signals of how our natural environment is changing. They are one of the best-studied groups of insects and often respond quickly to changes in climate and the environment.
“Butterflies therefore function as important indicators of how nature is being affected by a warmer climate,” says Lars Pettersson.
Changes in land use, including through agriculture, also play an important role in butterfly occurrence, particularly for species whose distribution ranges are shrinking. The study covers 1,758 butterfly species from a total of 105 countries. Of these species, 80 percent had expanded their distribution ranges, while 27 percent had experienced a reduction in their range. The researchers also found shifts to higher or lower elevations in 22 percent of the species.
“So, there are both expansions and declines, depending on the species and the part of the world we are talking about,” explains Lars Pettersson.
Volunteer butterfly enthusiasts
Sweden is one of the countries where these changes are particularly well documented. Changes in butterfly distribution are also especially clear in Sweden because of the country’s elongated north–south shape.
“We are seeing species expanding northwards and species retreating from the southern parts of the country,” says Lars Pettersson.
Several butterfly species are declining sharply in southern Sweden, including the Scarce Copper, the Mazarine Blue and the Small Pearl-bordered Fritillary. At the same time, these species still have strong populations further north.
“In southern Sweden, we are losing more species than we are gaining, while in some areas further north the opposite may be true, as southern species expand northwards,” says Lars Pettersson.
He points out the great value of long-term monitoring of biodiversity. At the same time, the study shows that there are significant gaps in our knowledge, particularly in tropical regions.
An important Swedish contribution to the study comes from the several hundred volunteers who have systematically collected data on Sweden’s butterflies over a long period of time. These long-term datasets help make it possible to track how the butterfly fauna is changing over time.
“The research study really demonstrates how valuable these voluntary efforts can be. Both here in Sweden and around the world, researchers and nature enthusiasts are working to learn more about butterfly populations. When such observations are collected over long periods and from many parts of the world, we can begin to see the major changes,” says Lars Pettersson.
The study has been published in the scientific journal Nature Ecology & Evolution: Extensive climate-induced range shifts in butterflies across the globe.