Despite nature conservation areas established in Bavaria, Germany, researchers have seen a steady decline in some of the country's butterfly species. In fact, populations once comprised of 117 butterfly species and diurnal moths have dwindled to only 71 species.
Researchers from Technical University Munich (TUM) and Bavarian State Collection of Zoology (ZSM) found that habitat specialists are at the greatest risk of extinction. In contrast, species such as brimstone, meadow brown and small heath butterflies have no specific ecological demands and tend to have more modest requirements when it comes to choosing living quarters and larval host plants.
Using butterfly records from 1840 until today, researchers found the species' decline is largely due to high emissions of reactive nitrogen. This, researchers say, is linked to the burning of fossil fuels, industrialization and intensive agriculture of recent decades.
All of the data evaluated was collected from areas around the city of Regensburg in Bavaria, where rare oligotrophic grasslands and, therefore, oligotrophic biotopes for butterflies and other insects dominate. About 45 hectares of land in this area has been designated as a conservation area since 1992.
"The observations carried out over a period of 200 years confirm the general trend of a decline in habitat specialist species despite the fact that these species are the target of nature conservation measures," explained Jan Christian Habel, one of the study researchers from TUM's Terrestrial Ecology Research Group.
Researchers also found that the composition of butterfly species has changed. Although the region was one populated by a diverse butterfly community, it is now dominated only by a few habitat generalists - those that are more flexible and resistant to nitrogen pollution.
Between 1840 and 1849, there were about 117 butterfly species and diurnal moths, but between 2010 and 2013 only 71 species were counted. Since habitat specialists require certain larval host plants and habitat structures to survive, many have disappeared, as nitrogen emissions promote the growth of dandelions, thistles and sorrel instead.
"These changes in the environment have a very serious impact on the habitat specialists," Habel added. "Most conservation areas are very small and isolated and sparsely distributed in the landscape. Moreover, atmospheric nitrogen does not respect the boundaries of the protected areas."
Despite climate warming, thermophilic species - those that like warm and dry conditions - also appear to be in decline.
"The vegetation is growing faster due to the nitrogen inputs," Habel explained. "This creates more shade close to the ground, which is too much shade for heat-loving butterflies. The question that emerges here is whether the established network of fauna-flora habitat conservation areas will enable us to achieve effective nature conservation in the long term. The answer is clearly no."
Their findings were recently published in the journal Conservation Biology.
