Since grassland butterflies depend heavily on several plant species for food, shelter, and as hosts for larvae, the team hypothesised roads would decrease the species richness and abundance of butterflies and plants. Roads could also alter species composition of a community in such a way that some species may tolerate life next to a road, while others avoid it.
Roads also change insect communities in a different manner. Road verges, which are linear grassy structures accompanying roads, are regarded as a good replacement habitat for plants and may act as their dispersal corridors. Though, this potentially good effect might be diminished by road mortality, which can be high in butterflies.
Grasslands near Kraków, Poland.
The study was conducted in grasslands near Kraków, Proszowice and Tarnów in southern Poland. The team selected 10 grassland patches adjacent to roads with heavy traffic (50–100 vehicles per hour) and 10 reference (control) grassland patches located at least 200 m from major roads. The grassland patches were similar in size, ranging from 7.8–13.5 hectares. The traffic on the studied paved roads was average for the traffic volume on Polish roads.
Differentiation of butterfly species in different parts of the grassland patches adjacent to roads with traffic and these far from roads.
Butterflies were counted along transects in twelve surveys during April to September in 10 -14 day intervals. Consecutive transect counts were established to cover the entire flying period of butterfly species with different biologies. The observer travelled the centreline of a 5m wide transect.
During each visit, the team also collected roadkilled butterflies along the 200 m part of the road neighbouring the studied grasslands near both major roads and unpaved roads, however, no dead butterflies at the latter.
Using a generalized linear model, with a negative binomial error structure and log-link function to test differences in butterfly and plant species richness, butterfly abundance and plant cover in survey areas was measured.
The study found that roads had a subtle effect on butterfly communities. Contrary to the stated hypothesis, grassland patches neighbouring roads did not have lower butterfly richness nor abundance compared to grassland patches located farther from roads.
Authors: Piotr Skórka, Magdalena Lenda, Dawid Moroń.