This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A new study led by researchers at the Museum für Naturkunde Berlin shows that Berlin's dragonfly populations have declined by more than half since 1963, while populations of frogs, toads and newts have fallen by more than three-quarters since 1981. The study also involved Berlin-based experts Falk Petzold and Klaus-Detlef Kühnel, who coordinate the data series.
The research, which was carried out as part of the project "Understanding Diversity—Exploring and Experiencing Nature," was published in the journal Global Change Biology Communications. Dragonflies and amphibians lead a dual life: as larvae in water and as adults on land. It is precisely this dependence on two habitats that makes them so vulnerable.
For the study, the researchers analyzed two extensive, previously unpublished datasets: the Berlin Dragonfly Database, containing almost 24,000 observations dating back to 1850, and the Berlin Amphibian Dataset, comprising more than 16,000 records dating back to 1970, compiled by nature conservation organizations and specialist societies. The analysis included 16 bodies of water that had been surveyed regularly and in a comparable manner over several decades: from forest lakes in Grunewald to bog waters in Köpenick and ponds in Marienfelde and Tegel. The result is clear: Between 1963 and 2023, dragonfly populations declined by an average of 51%.
Among amphibians, the decline was even more pronounced, at 76% between 1981 and 2022. "Given the general trend of species decline, it is unfortunately no surprise that both groups are in decline. What is remarkable, however, is how much more severely the amphibians are affected," says Silvia Keinath, lead author of the study and a researcher at the Museum für Naturkunde Berlin.
"Frogs, toads and newts are significantly less mobile than dragonflies and are therefore particularly vulnerable when migration routes between spawning grounds and terrestrial habitats are disrupted by roads, development or small bodies of water drying up." Dragonflies, on the other hand, being good flyers, can more easily colonize new bodies of water, but they too remain vulnerable to changes such as ponds drying up too early and the loss of suitable habitats. The Living Planet Index aggregates the trends in many individual populations into a single trend value—similar to a stock market index, which reflects not the absolute number of animals but the average change in their populations. This makes it possible to visualize how the populations of different species are changing over long periods, even when the underlying data has been collected in a patchy and inconsistent manner.
One reason for the observed declines could, quite literally, be on our doorstep: When cross-referencing with recent reports on small water bodies in Berlin, the team found that 36 of the water bodies originally studied have since dried up completely, partly as a result of falling groundwater levels and a lack of rainfall. Such permanently lost water bodies could no longer be included in the calculation of the index at all, as there was no longer a continuous time series available. The actual losses are therefore likely to be even higher than the study indicates.
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