The diversity of butterflies in Central Europe has been declining for a long time. According to one study, two factors in particular affect the animals, so that these insects have disappeared in two major waves over the past 100 years.
This is the report of a research team from Austria, Germany and Poland after analyzing observation data in the Austrian state of Salzburg over a period of 100 years. The populations of butterflies initially fell there, especially at the beginning of the 20th century and then in the 1960s.
The main causes were changes in the landscape and the intensification of agriculture. The analysis also shows that the loss of species has stopped since the mid-1990s, apparently as a result of nature conservation measures.
The extinction of species specialized in wetlands has been slowed down because of the protected areas designated there.
Jan Christian Habel, University of Salzburg
Many studies show that both the biodiversity and the mass of insects in Central Europe have shrunk drastically over the past few decades. In order to determine the causes of this development over a longer period of time, the researchers led by Jan Christian Habel from the University of Salzburg evaluated almost 60,000 observation data on 168 species of butterflies.
Both the group of butterflies and the study region in the state of Salzburg are well suited to reflecting the general development of insects in Central Europe. Since butterflies inhabit many different habitats, the researchers assume that the identified trends also apply to other groups of insects.
“Our study area is an example of the general intensification of agriculture in large parts of Central Europe, with all its negative effects on biodiversity,” write the authors in the journal Science of the Total Environment.
The work is based on data and records from the Haus der Natur Salzburg, which go back to the year 1920. “They show that the numbers of numerous species were already declining at the beginning of the last century,” says co-author Thomas Schmitt from the Senckenberg German Entomological Institute in Müncheberg near Berlin. A second major extinction event then took place in the 1960s.
Accordingly, in the first wave of species extinction, those butterflies in particular that lived in sensitive ecosystems such as moors disappeared. “Such habitats were already being destroyed at the end of the 19th century, during the period of the most intensive population growth in Europe, due to the strong expansion of agricultural and forestry use,” says lead author Habel. During this period, for example, many moors and wet meadows were drained, but former dry wasteland was also put under management. To this day, this is particularly damaging to those species that are specialized in these ecosystems, such as the raised bog yellow (Colias palaeno).
The second wave began in the mid-20th century. In the 1960s in particular, the diversity of butterflies decreased, mainly due to the dwindling quality of habitats. “Responsible here seems to be the industrialization of agriculture that was beginning at this point in time, with the intensive use of pesticides and artificial fertilizers,” says Schmitt. As a result, many near-natural elements of the cultural landscape, such as poor valley meadows rich in flowers and rich in biodiversity, disappeared. “This trend has continued to be negative to this day,” says Schmitt.
From the 1970s, the loss of species also reached the alpine mountain regions, where many landscapes were destroyed at that time, for example through regular mowing, more intensive livestock farming, fertilization and sowing of non-native plants. In general, according to the team, those species that specialized in specific landscapes in particular disappeared. It is precisely these species that should be given priority protection through greater conservation of their habitats.
The study also contains good news: the number of endangered species has not decreased since around 1994. “The extinction of species that specialize in wetlands was also slowed down because of the protected areas designated there,” says Habel. Since then, however, diversity has remained at a low level.
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