Roads may act as barriers to flying insects: species composition of bees and wasps differs on two sides of a large highway

Abstract

Roads may act as barriers to animal movements, but direct barrier effects on insects have rarely been studied. In this study we collected data on bees and wasps along two sides of a large road in Sweden using yellow pan traps. We then analyzed if the species composition differed between the two sides of the road; first for the whole community, and then only for the smallest species (which typically are poorer dispersers). As a complement, we analyzed if different vegetation variables differed between the two sides of the road, as this may also affect differences in species composition. Finally, we analyzed if species richness and abundance in general differed between the two sides and how these two response variables were explained by the vegetation variables. There was a significant difference in species composition between the eastern and the western side of the road when analyzing the whole community, and this relationship became even stronger when the largest species were excluded. The vegetation variables did not strongly differ between the two sides, and there was no difference in species richness and abundance of bees and wasps either. Abundance was, however, explained by the number of flowering plants in the surroundings of the trap. Even though using a rather limited data set, our results indicate that large roads may act as barriers on the movement of bees and wasps, especially for small species with poor dispersal ability. On the other hand, road verges may be important habitat for many species, which leads to a potential conflict that is important to consider in the planning of green infrastructure. RESEARCH ARTICLE Launched to accelerate biodiversity conservation A peer-reviewed open-access journalPetter Andersson et al. / Nature Conservation 18: 47-59 (2017) 48

Estimates of accessible food resources for pollinators in urban landscapes should take landscape friction into account

“…However, the commonly used distanceweighted measure (e.g., Hanski 1994, based on the Euclidian distance) was not better than simple summations of habitat in buffer circles in our urban landscape study area, which disagrees with earlier studies (Moilanen andNieminen 2002, Ranius et al 2010). The barrier effect of large roads agrees with recent research showing clear differences in species composition of bees and wasps between two sides of a large highway (Andersson et al 2017). Potential barriers, such as large roads, seem to be particularly important to consider as the simplified friction-type measure (where we only had friction for roads, other paved ground and built-up land) also significantly explained both species richness and abundance.…”

“…1). Hence, with high friction (>40) even rather narrow (~10 m) landscape elements (if stretching across the landscape) can become complete barriers for the species when the maximum distance is 400 m. In this study, large roads, other paved ground, buildings, and open water were given friction values that make them complete barriers (Andersson et al 2017). This measure also can account The amount of food habitat weighted by the Euclidian distance using a negative exponential function.…”

“…The number of bands (n) was eight (i.e., 400 m divided by 50 m). See for potential barriers in the landscape, which recently has been shown to affect the species composition of bees and wasps (Andersson et al 2017). The first, a = 0.01, represents a steep dispersal kernel that gives relatively low weight (<0.14) for habitat >200 m away, while a = 0.002 represents stronger dispersers with a corresponding weight of 0.67 at 200 m (Fig.…”

“…However, maintaining such services in a sustainable perspective require an urban landscape where bees and wasps can easily move between important habitats. Therefore, they may be sensitive to potential barriers such as large roads in the landscape (Andersson et al 2017). Therefore, they may be sensitive to potential barriers such as large roads in the landscape (Andersson et al 2017).…”

“…These measures account for landscape friction by using costweighted distances rather than Euclidean distances (e.g., Adriaensen et al 2003). However, in urban environments the less complex measures (based on the Euclidian distance) may become less reliable as, for example, roads and built-up land can function as barriers (Peralta et al 2011, Andersson et al 2017) that reduce the accessibility to some of the surrounding habitat. The latter are generally also more practically applicable for landscape planners and field conservationists.…”