From the cabbage white butterfly to the swallowtail – which European butterfly species can cope with increasing urbanization and which cannot? A study sheds light on this question as well as the causes of the different adaptability. Some generalists can benefit from this, but for most species the human habitats are problematic. In order to preserve biodiversity, the needs of specialized butterflies should therefore be given special consideration in urban planning, say the researchers.
Near-natural landscapes are increasingly turning into urban settlement areas: Worldwide, settlement and cities are forecast to grow by two to three million square kilometers by 2050. Where forests and meadows once provided a habitat for animals and plants, sealed areas and green spaces planted according to human preferences are now spreading. How wild animals can adapt to such habitat changes has so far mostly been studied in mammals and birds. The researchers around Corey Callaghan from the German Center for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, however, have now turned to a special group of insects: butterflies.
Dissemination data evaluated
To find out how the butterflies react to increasing urbanization and which species can adapt to it, the scientists evaluated over 900,000 entries on 158 species in Europe from the Global Biodiversity Information Facility. “In our study, it was an advantage that these insects are popular with many people, which gave us a relatively good database,” says Callaghan. His colleague Henrique Pereira from the Martin Luther University Halle-Wittenberg continues: “Most of the butterfly observations we used from the database were compiled by volunteers from all over Europe. Anyone can use smartphone apps such as iNaturalist or naturgucker to help increase knowledge about the effects of our way of life on biological diversity ”.
By evaluating the distribution data, the researchers were able to Butterfly species values of city affinity assign that range from minus to plus. According to this, 79 percent of butterfly species avoid urban areas. This applies most of all to the lesser maize bird (Euphydryas maturna). This species feeds exclusively on ash trees and needs moist, light forests as a habitat. But there are also some species that tend to appreciate the urban environment: 25 of the 158 butterfly species were more common there than in other habitats. A real city butterfly is, for example, the yellow C butterfly (Polygonia egea) or the well-known cabbage white butterfly (Pieris rapae). “It was surprising that we found such clear patterns across the entire European continent. The degree of city affinity indicates which species are likely to be among the winners and losers of urbanization, ”says Callaghan.
Generalists versus specialists
By combining the results with information on the life style of the butterfly species, the researchers then determined which characteristics give the species their urban affinity or aversion. It turned out that generalists in particular can adapt well to urban habitats – those species that feed on many different plants and can withstand large temperature fluctuations. In addition, a common characteristic of the winners was that they exhibited longer flight activity over the year and that they reproduced several times a year. Specialized species, on the other hand, which are heavily dependent on certain plants and climatic conditions, are expected to disappear more and more in the course of urbanization, say the scientists.
“We were able to show that characteristics such as temperature and habitat preferences can be used as clues to predict which species are most sensitive to human activities in order to prioritize them in protective measures,” says co-author Diana Bowler from Friedrich-Schiller -University of Jena. According to the scientists, one possibility of curbing the loss of biodiversity through urbanization is the targeted planting of host plants for the specialized butterflies as part of urban planning. But the citizens are also asked: “Every garden owner can make a contribution by choosing native plants,” says Callaghan in conclusion.
Source: German Center for Integrative Biodiversity Research, specialist article: Global Change Biology, doi: 10.1111 / gcb.15670