27.09.2024
Pollinating insects such as bumblebees play a crucial role in plant reproduction, not only by enabling seed production but also by facilitating the exchange of genetic information. This is particularly important in agricultural landscapes, where plant populations are often spatially separated by settlements, fields and roads. Researchers, including those from the Leibniz-Centre for Agricultural Landscape Research (ZALF), have investigated how different landscape elements influence the foraging routes of bumblebees in such agricultural landscapes and how this affects the genetic diversity of the wild plant populations. Their findings were recently published in the journal “Ecology and Evolution”
For their study, the researchers looked at a plant species found in many mixed deciduous forests in Europe - Solomon's seal (Polygonatum multiflorum). The flowers are pollinated by, among others, the common carder bee (Bombus pascuorum). The study showed that certain landscape features, such as maize fields and grassland, influence the foraging of bumblebees and thus the genetic exchange between plant populations.
Unexpected effect of maize fields
"When maize fields bordered the studied forest patches, a positive effect on the genetic exchange of Solomon's seal population was observed," explains Jannis Feigs, a PhD student in the 'Biotic Interactions between Forest and Agricultural Areas' working group and lead author of the study. "Since maize is not a food source for bumblebees, they look for nectar and pollen elsewhere - for example, on the plant we studied, the Solomon's seal."
In contrast, the semi-natural grasslands offered bumblebees plenty of food, so they did not have to travel the long distances to the nearest forest. "In these cases, we observed that the bumblebees flew among the forest patches less often. This influenced the genetic diversity of the plant populations," Feigs continues.
The results of the study clearly show that the composition of the landscape around forested areas is crucial for the movement patterns of bumblebees and thus for the genetic exchange of plants.
No free pass to grow more maize
Although the maize fields had a positive effect on the Solomon's seal, the study should not be seen as an argument for increased maize cultivation. Rather, it highlights the complex ecological relationships and conflicting objectives in landscape planning. Because maize fields do not provide food for pollinators, they represent a barrier in the landscape that can be used to guide pollinator movements. Extensive grasslands, on the other hand, support a wide variety of plant species and provide habitats and food sources for many insects, birds and other animals. It is therefore important to create a balanced mix of agricultural land and natural or semi-natural habitats.
Agricultural landscapes are patchworks
Solomon's seal is a typical forest herb, found mainly in large forests. Nowadays, its natural habitats are often separated by roads, fields and settlements. This means that from the plants' point of view, the agricultural landscape is like a patchwork. The technical term for this is habitat fragmentation. It is considered one of the causes of species extinction in Europe. As genetic exchange becomes less frequent, the gene pool within a population becomes depleted, leading to a higher risk of extinction.
Pollinators can fly over roads and fields, allowing genetic exchange between plants despite spatial separation. Bumblebees in particular play an important role, as they often travel long distances.
Methodological approach
The researchers captured bumblebees in different forest areas in Germany and southern Sweden and collected leaf samples from several Solomon's seal populations. They used microsatellite markers to analyze the genetic structure of the collected samples. Since bumblebees live in colonies of up to 150 genetically identical workers, the genetic data can provide information on how far the animals traveled between their nesting sites and the places where they were caught.
The researchers then used aerial imagery and georeferenced data to characterize the landscape surrounding the forest plots and correlated this information with the genetic data from the bumblebees and plants.
Project partner:
- Leibniz Centre for Agricultural Landscape Research (ZALF) e.V, Müncheberg, Germany
- Southern Swedish Forest Research, Centre, Swedish University of Agricultural Sciences, Alnarp, Sweden
- Vegetation Ecology and Conservation Biology, Institute of Ecology, FB 2, University of Bremen, Bremen, Germany
Funding:
This study was funded by the Deutsche Forschungsgemeinschaft, Grant/Award Number: HO 4742/2-1, KR 5060/1-1 and 1067/2-1, the FWO Scientific research network FLEUR, the German Federal Ministry of Food and Agriculture (BMEL) and the Ministry for Science, Research and Culture of the State of Brandenburg (MWFK).
