The diversity of butterflies, which was once so great, continues to decline. Researchers have now investigated the reasons for this and the timing of this loss of species among butterflies using the example of the Salzburg region. They found that the decline in butterfly diversity and numbers over the past 100 years has not been continuous, but in two large waves. They are closely related to landscape changes and agricultural intensification.
Butterflies are insects and are extremely important for our flora: Similar to bees, they feed on pollen and nectar and thus ensure that plants are pollinated. Some plant species are even exclusively pollinated by butterflies. But the butterflies are in a bad way: the trend towards monotonous farmland and away from colorful flower meadows is depriving the butterflies of their source of food and depriving them of safe places to lay their eggs. However, this is not a development of recent years, but started much earlier. When and why, however, has so far been unclear.
Species decline reconstructed
Therefore, a team of scientists led by Jan Habel from the University of Salzburg has now examined the species decline of butterflies in more detail using the example of the Austrian state of Salzburg. The subject of their study were 168 butterfly species, which were examined using almost 60,000 observation points over an area of over 7,000 square kilometers. Among them were the high moor yellow butterfly (Colias palaeno), which only occurs in undisturbed high moor areas in the region, and the red-brown meadow bird (Coenonympha glycerion), which is also becoming increasingly rare in Upper Austria. In addition, the researchers based their analysis on data and records from the Haus der Natur in Salzburg going back to 1920.
The results make it clear that numerous species were already in decline at the beginning of the last century and that there were two major waves of species loss among moths. "Each species reacts differently to changes in our environment - so there are specific factors for each species that lead to the extinction of local populations and ultimately to the complete disappearance of the species," explains co-author Thomas Schmitt from the Senckenberg German Entomological Institute in Müncheberg . The biologists were able to determine what these were by comparing them with historical land use data, among other things.
Decline in two big waves
A first wave of species extinction mainly affected butterflies that lived in sensitive ecosystems such as moors. “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. During this period, for example, many moors and wet meadows were drained, but former dry wasteland was also transferred to management,” reports Habel. The progressive destruction of the moor ecosystem then triggered a population decline of species such as the raised bog yellow butterfly, which has continued to this day, because these species are exclusively specialized in the environmental conditions of the moors and have difficulty escaping to other ecosystems.
"A second major extinction event then took place in the 1960s," reports Schmitt. The reduction in habitat quality in particular led to a loss in butterfly diversity. During this period, the scientists were able to detect increased declines among the species that lived in the meadows of the Austrian lowlands. "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. As a result, many natural elements of the cultural landscape disappeared, such as poor, flower-rich valley meadows with their high biodiversity. This trend has continued to be negative to this day,” explains Schmitt. The team's evaluations also show that butterfly diversity in mountainous and alpine areas has been declining since 1980 - the destruction of natural and semi-natural landscapes has also reached the mountainous regions since 1980.
Conservation has partially helped
But the scientists were also able to find positive things, because the nature conservation measures that were introduced in the mid-1990s also made themselves felt in the population data: the species listed as endangered on the Red List have not decreased since then, as the evaluations showed . "The extinction of species that specialize in wetlands was also slowed down because of the protected areas designated there - although diversity has remained at a low level since then," says Habel.
According to the research team, the alarming decline in butterflies is not an exception, but a warning for the diversity of other animal species as well. This is because butterflies inhabit a wide variety of habitats and their population trends are consistent with many other groups of insects. The butterflies are therefore ideally suited to show general trends in biodiversity.
Source: Senckenberg Research Institute and Natural History Museums, Article: Science of the Total Environment; doi: 10.1016/j.scitotenv.2022.158315