Butterflies in sharp decline
The diversity of butterflies has changed since 1900. A new study now provides the first inventory underlining the decline of butterflies in Denmark. It shows that twelve species (10% of Danish butterfly species) have gone extinct during the last fifty years. This decline is continuing and a number of species are so critically endangered today that they may become extinct within the next few years. These results were published by researchers from the University of Amsterdam, Naturalis Biodiversity Center, and scientists from universities in Denmark and Germany in the scientific journal Diversity and Distributions.
Specialisation not always the key to success
A significant difference was found between those species that have gone extinct, and those that are still doing relatively well in the Danish countryside. ‘The greatest losses have mainly been observed for butterfly species that live in the woods. Out of the twelve species of butterflies that have been lost, ten were native to woodland habitats. The species that have gone extinct in Denmark include attractive and colourful butterflies such as the Cryptic Wood White, Duke of Burgundy Fritillary, and Clouded Apollo,’ says Anne Eskildsen, who led the project as part of her PhD thesis at Aarhus University, Denmark. Conditions are hard not only for species with woodland habitats, but also for species that are associated with rare host plants. Generalist species do much better as they can thrive in a number of different habitats.
Combining old-school with state-of-the-art science
Measuring the decline of the Danish butterflies was possible by using a database containing almost half a million butterfly observations made all over Denmark during the period 1900 to 2012. The database contains historical data from collections curated at natural history museums, entomological societies and private collections. More recently, data has become available from atlas studies and popular citizen science databases, such as DOFbasen (Danish Ornithological Association database) and Fugle og Natur (Birds and Nature). ‘Anne Eskildsen has done an amazing job with collecting, aggregating and handling these big and diverse datasets’, says Daniel Kissling from the Institute of Biodiversity and Ecosystem Dynamics (IBED), University of Amsterdam, who was co-supervisor of the PhD project. ‘Using this impressive data set in combination with advanced new statistical methods made it possible to map what the butterfly population looked like in Denmark a century ago. This made it possible to understand the extent of the decline in the Danish butterfly population up to the present day’, Kissling continues.
A new ‘butterfly effect’
The reasons for the enormous decline in the species of Danish butterflies are mainly found in the intensification of forestry and agriculture. This has resulted in limited living space in the modern landscape for butterflies to flourish. The high sensitivity of butterflies and their rapid response to even small changes in their environment provide researchers with an early warning signal for changes in nature. Detection of these changes allows for effective mitigation of the problem, even though conditions currently look bleak for the Danish butterflies. The scientists therefore argue that targeted efforts are needed to improve the remaining habitats for butterflies in Denmark.
Eskildsen, A., Carvalheiro, L.G., Kissling, W.D., Biesmeijer, J.C., Schweiger, O. & Høye, T.T. (2015) Ecological specialization matters: long-term trends in butterfly species richness and assemblage composition depend on multiple functional traits. Diversity and Distributions, in press.