Insect change among dragonflies in Germany

Aerial acrobatics in riverside areas in their sight: The distribution of dragonfly species in Germany has changed dramatically in recent years — there are winners and losers in environmental changes, according to a study. Accordingly, there was a significant increase in the number of species that live near rivers and prefer higher temperatures. On the other hand, there was a decrease in the numbers of dragonflies, which adapted to the stagnation of water. Scientists explained that the trends in question are due in part to successes in protecting the environment, but the effects of climate change are also emerging.

Germany is the land of dragonflies: nowhere else in Europe is there such a diversity of species in these flying insects in aquatic ecosystems. However, due to human influence, this habitat sometimes undergoes significant changes. How has dragonfly dealt with it over the past few decades? Researchers led by Diana Boehler of the German Center for Integrative Biodiversity Research in Leipzig investigated this question. They analyzed more than 1 million data entries on the occurrence of 77 species of dragonfly in Germany from 1980 to 2016. Most of the information came from volunteer citizen scientists and the German-speaking Society of Audiologists (Dragonfly Scientists).

It increases but also decreases

Basically, the study shows: While there has been a general decline in the population and distribution of many other insect groups in recent decades, a mixed picture emerges of a dragonfly – scientists have found a spin. According to this, the distribution of 45 percent of the species has increased over the past 35 years and has remained stable at 26 percent. In contrast, the researchers found a 29 percent decrease in the 77 German dragonfly species. As they assert, many of these shrinking species are already endangered, and therefore should now be the focus of protection measures.

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The blue-winged Demoiselle (Calopteryx virgo) is a species that has benefited from water protection in Germany since 1980. (Photo: Andre Günther)

By looking at the characteristics of the species, it also becomes clear which factors underlie the respective development trends. The winners from the developments of recent decades are the dragonfly, which prefers to live on the banks of running water, and the thermophilic species. Species that were once rare, such as the fire dragonfly and the small scale eye, are now more common in Germany. These species prefer higher temperatures, so their increases in Germany are likely due to long-term climate change,” explains Buller.

Climate change and environmental protection

On the other hand, researchers attribute positive trends in river-adapted species to more satisfactory effects—to successes in protecting these habitats. “Growth in this species shows recovery from the effects of past water pollution and the almost complete destruction of the natural floodplains,” says co-author Klaus-Juergen Kunz of the German-speaking Association of Audiologists. Background: In Germany, the first projects to improve fresh water quality and protect rivers were launched in the 1990s.

Unfortunately, the positive developments are offset by the alarming decline in 29 percent of German dragonfly species. As the researchers report, the losers in recent decades are species that prefer lower temperatures and stagnant water such as swamps and swamps. They depend on shallow or small bodies of water, which are becoming increasingly scarce due to drought and low groundwater levels. The consequences of climate change appear to be causing problems for this species. “They suffer a lot from degradation in their environment,” says Bowler. Here we continue to see significant challenges to protect and conserve these habitats.”

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In addition to planning measures to improve biodiversity, scientists also see the need for more research. In conclusion, they emphasize the important role of volunteer citizen scientists as an informational one: “Our study confirms the significant contribution that the commitment of nature lovers can make to the investigation of species occurrence,” says senior author Aletta Bonn of the Helmholtz Center for Environmental Research in Leipzig.

Source: German Center for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, specialized article: Diversity and Distributions, doi: 10.1111/ddi.13274

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