Impacts of multiple pollutants on pollinator activity in road verges

Abstract

To tackle pollinator declines, there is a major need to increase the quantity of flower‐rich habitats. Road verges offer one such opportunity but are exposed to diverse forms of pollution from roads and road traffic. We carried out a broad initial assessment to establish if and how pollution affects the quality of road verges as pollinator foraging environments. We assessed the spatial distribution of pollution, flowers and pollinators in road verges, then used field experiments to simulate and measure the impacts of four ubiquitous and little studied forms of road pollution (noise, turbulence, dust and metals) on pollinator densities and foraging behaviour. We found that pollinators in road verges were exposed to noise, turbulence, dust and metal pollution, which decreased with distance from the road edge but, with the exception of turbulence, extended more than 8 m into road verges. Pollinator densities were lower closer to the road edge—particularly within first 2 m (55% lower than at 7–9 m)—where pollution is greatest. This was despite a similar density and species richness of flowers. Simulated turbulence deterred pollinators by causing intermittent disturbance (reducing visit duration by up to 54%), and some pollinator taxa preferentially avoided concentrations of metals that were more frequently found in flowers within 2 m of roads (resulting in up to 75% fewer visits), while noise and dust had no apparent effect. Synthesis and applications. Pollinators in road verges are exposed to many forms of pollution, and we found impacts of roadside‐realistic levels of turbulence and metals on pollinator densities and foraging behaviour. Although the findings suggest that road verges are largely suitable for pollinator conservation, management enhancements should prioritise areas more than 2 m from the road edge, and verges along roads with relatively lower traffic densities.

Traffic patterns, more than adjacent land use, influence element content of roadside forbs for insect pollinators

“…Our results demonstrate that the lead signature in foliar chemistry is long‐lasting, but even over decades, it has not spread through the environment; it remains most concentrated close to the roadside. Although previous work has found that urban heavy metals can negatively affect the performance of insect pollinators such as bees (Meindl & Ashman, 2013; Phillips et al., 2021; Rothman et al., 2020; Sivakoff et al., 2020), our data suggest that none of the roadside forb species considered in our study are accumulating metals to levels known to be toxic to larval butterflies and moths, at least in terms of cadmium, lead, copper, nickel and zinc (Cheruiyot et al., 2013; Coleman et al., 2005; Davis et al., 2001; Gintenreiter et al., 1993; Jin et al., 2020; Martens & Boyd, 1994; Shephard et al., 2020; Table 3). For instance, across all forb species considered, mean and maximum lead concentrations ranged from 0.166 to 1.06 and 0.332 to 1.65 ppm, respectively (Table 3), concentrations far below those shown to induce mortality in moths (e.g.…”

Metals and metal isotopes incorporation in insect wings: Implications for geolocation and pollution exposure

“…Plants are known to uptake and regulate metals in a species-specific manner; thus, this relatively high hostspecificity will likely minimize potential discrepancies in metal signatures associated with differences in larval host plant species (McLean et al, 1983;Tibbett et al, 2021). Third, metal exposure is of particular concern for monarchs because milkweed is often found in disturbed habitats, such as roadsides, which often correlates with higher pollution exposure (Phillips et al, 2021). As for most insects, the incorporation and toxicology of metals in monarch butterflies are mostly unknown, although Zn has been shown to decrease larval survival under some conditions (e.g., when individuals have low access to macronutrients; Shephard et al, 2020Shephard et al, , 2021Shephard et al, , 2022.…”

Metals and metal isotopes in insect wings: Implications for diet, geolocation and pollution exposure

“…Plants are known to uptake and regulate metals in a species-specific manner; thus, this relatively high host-specificity will likely minimize potential discrepancies in metal signatures associated with differences in larval host plant species (McLean et al 1983, Tibbett et al 2021. Third, metal exposure is of particular concern for monarchs because milkweed is often found in disturbed habitats, such as roadsides, which often correlates with higher pollution exposure (Phillips et al 2021). As for most insects, the cycling and toxicology of metals in monarch butterflies are mostly unknown, although zinc has been shown to decrease larval survival (Shephard et al 2020).…”

“…2021). Third, metal exposure is of particular concern for monarchs because milkweed is often found in disturbed habitats, such as roadsides, which often correlates with higher pollution exposure (Phillips et al . 2021).…”