The aerial acrobats of the riparian zones in their sights: The distribution of dragonfly species in Germany has changed significantly in recent years – there are winners and losers in environmental changes, shows a study. Accordingly, there has been a significant increase in the number of species that live near rivers and prefer higher temperatures. On the other hand, there was a decline in dragonflies, which are adapted to stagnant water. The respective trends are partly due to successes in environmental protection, but the effects of climate change are also emerging, the scientists explain.
Germany is dragonfly land: Nowhere else in Europe is there such a diversity of species in these flying insects of the aquatic ecosystems. However, due to human influence, these habitats are sometimes subject to considerable change. How did the dragonflies cope with it over the past few decades? The researchers led by Diana Bowler from the German Center for Integrative Biodiversity Research in Leipzig investigated this question. They analyzed over a million data entries on the occurrence of 77 dragonfly species in Germany from 1980 to 2016. Most of the information came from volunteer citizen scientists and from the Society of German-speaking Odonatologists (dragonfly scientists).
Increases, but also decreases
Basically, the study shows: While there has been a general decline in populations and distribution for many other insect groups in recent decades, a differentiated picture emerges for dragonflies – the scientists found both increases and decreases. 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 declines in 29 percent of Germany’s 77 dragonfly species. As they emphasize, many of these shrinking species are already endangered and should therefore now be the focus of protective measures.
By looking at the characteristics of the species, it also became clear which factors underlie the respective development trends. The winners of the developments in recent decades are dragonflies, which prefer to live on the banks of running waters, and heat-loving species. “Species that were previously rare, such as the fire dragonfly and the small shell eye, have now become much more common in Germany. These species prefer higher temperatures, so their increases in Germany are most likely due to long-term climate change, ”explains Bowler.
Climate change and environmental protection
In contrast, the researchers attribute the positive trends in species adapted to rivers to more gratifying effects – to successes in protecting these habitats. “The growth in these species shows a recovery from the effects of earlier water pollution and the almost complete destruction of natural floodplains,” says co-author Klaus-Jürgen Conze from the Society of German-speaking Odonatologists. The background: In Germany, the first projects to improve the quality of fresh water and to protect rivers were launched back in the 1990s.
Unfortunately, however, the positive developments are offset by the worrying decline in 29 percent of Germany’s dragonfly species. As the researchers report, the losers in recent decades are species that prefer cooler temperatures and stagnant water such as swamps and bogs. They depend on small or shallow bodies of water, which are becoming increasingly rare due to drought and low groundwater levels. The consequences of climate change are apparently causing problems for this species. “They are suffering a lot from the decline in their habitat,” says Bowler. Here we still see great challenges for the protection and preservation of these habitats ”.
In addition to planning measures to improve biodiversity, the scientists also see a need for further research. In conclusion, they emphasize the important role of volunteer citizen scientists as informational: “Our study underlines the great contribution that the commitment of nature lovers can make in investigating the occurrence of species,” says senior author Aletta Bonn from the Helmholtz Center for Environmental Research in Leipzig.
Source: German Center for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, specialist article: Diversity and Distributions, doi: 10.1111 / ddi.13274