Butterflies under threat: biodiversity in danger
The deterioration and fragmentation of natural environments due to human activity have led to the depletion of biodiversity. Butterflies, the emblematic species of natural environments, are no exception: over the last 20 years, we have observed a 70% decline in the abundance of these species. Scientists have taken an interest in how these communities react and their role in farming environments, demonstrating the importance of preserving landscape connectivity in these areas.
The population of butterflies, so emblematic of open environments (prairies, farmland, etc.), has decreased by 70% over the last 20 years in Europe. The main cause is the fragmentation of natural environments and the intensification of farming practices in these land parcels. Implementing a green belt in farming environments, which would reinforce ecological networks necessary for fauna and flora, could stop this decline.
One research project  coordinated by Irstea looked at these communities from 3 angles:
- scientific: understanding how flocks of diurnal butterflies vary in relation to landscape characteristics and agricultural practices. The project carried out a sampling of butterflies in 3 regions and then analyzed the data from participatory monitoring as part of the Vigie Nature program led by the Museum of Natural History.
- legacy: preserving diurnal butterflies.
- social and anthropological: understanding what motivates different stakeholders, especially farmers, who often take part in participatory monitoring for butterflies in France.
Forests to the rescue?
"One of the main results to come out of the study was that having forests in the neighboring environment (afforestation near prairies, roads or highways) leads to a greater level of diversity among diurnal butterflies (forest and prairie butterflies)," explains Frédéric Archaux, researcher at the Nogent-sur-Vernisson Irstea Center. For butterflies that are dependent on prairies, this means a nighttime refuge, nectar when the prairies are mown, and a microclimate.
For the first time, the scientific team looked at landscape genetics. This is a new field that makes it possible to work on issues of population dynamics – a fundamental part of the green belt. "We have studied butterfly distribution (specifically the meadow brown – Maniola jurtina L.) not by monitoring individual journeys using sensors or telemetry (sensors installed on the butterflies’ backs), but by studying their genetic legacy and checking if two geographically close individuals are also genetically similar." This method makes it possible to quantify the flow of genes, rather than the flow of individuals, through the landscape.
|Anne Villemey (PhD student) is carrying out a transect survey of butterflies in Yonne (Burgundy) ©Irstea / F.Archaux||Field in Yonne (Burgundy) © Irstea / F. Archaux|
How it's done: scientists catch a butterfly and remove one of its legs to extract DNA (this does not affect the insect’s chances of survival). They are then able to study part of the DNA (the alleles) to identify specific genetic markers. Next, they calculate a similarity/kinship index between 2 individuals in relation to the landscape where the samples were taken. It is progress, although during the project, "a small proportion of genetic variability was due to landscape, perhaps due to the choice of species."
Adapting environmental management
The operational range of the green belt is conceived at a regional level, which generally corresponds to the scale of butterfly dispersal. The green belt can reinforce connections by recreating habitats as well as improving the quality of existing habitats. However, the study showed that the quality, rather than the layout, of grasslands and road or highway verges (plant height, plant quantity, floral diversity, etc.) is the determining factor.
"Local communities should not neglect work on agricultural practices," highlights Archaux. "Thus rather than transforming landscapes by recreating grasslands, even if these are carefully managed, it may be better to work with farmers to adapt some practices to the local situation, e.g., reconsidering mowing frequency, nearby pesticide and fertilizer use, etc. These actions make it possible to increase butterfly population levels, which mathematically increases the flow of individuals through a landscape." A final landscaping recommendation would be to encourage a mosaic of semi-natural herbaceous and wooded environments that support these species.
For more information
- Special feature. Green light for the Green and Blue Belt
- Publications. Science, Water and Land The Green and Blue Belt: regional action, now and tomorrow
- Consult the web page of the Forest Ecosystems (EFNO) research unit at the Irstea Nogent-sur-Vernisson Center
 LEVANA Project 2013-2016: funded by the Ministry of the Environment as part of phase 3 of the DIVA research program "Public Action, Agriculture and Biodiversity" on ecological networks. Partners: Irstea, INP ENSAT, Inra Bordeaux, CNRS, National Museum of Natural History. Coordinator: Irstea