Changing Bee and Hoverfly Pollinator Assemblages along an Urban-Rural Gradient

Abstract

BackgroundThe potential for reduced pollination ecosystem service due to global declines of bees and other pollinators is cause for considerable concern. Habitat degradation, destruction and fragmentation due to agricultural intensification have historically been the main causes of this pollinator decline. However, despite increasing and accelerating levels of global urbanization, very little research has investigated the effects of urbanization on pollinator assemblages. We assessed changes in the diversity, abundance and species composition of bee and hoverfly pollinator assemblages in urban, suburban, and rural sites across a UK city.Methodology/Principal FindingsBees and hoverflies were trapped and netted at 24 sites of similar habitat character (churchyards and cemeteries) that varied in position along a gradient of urbanization. Local habitat quality (altitude, shelter from wind, diversity and abundance of flowers), and the broader-scale degree of urbanization (e.g. percentage of built landscape and gardens within 100 m, 250 m, 500 m, 1 km, and 2.5 km of the site) were assessed for each study site. The diversity and abundance of pollinators were both significantly negatively associated with higher levels of urbanization. Assemblage composition changed along the urbanization gradient with some species positively associated with urban and suburban land-use, but more species negatively so. Pollinator assemblages were positively affected by good site habitat quality, in particular the availability of flowering plants.Conclusions/SignificanceOur results show that urban areas can support diverse pollinator assemblages, but that this capacity is strongly affected by local habitat quality. Nonetheless, in both urban and suburban areas of the city the assemblages had fewer individuals and lower diversity than similar rural habitats. The unique development histories of different urban areas, and the difficulty of assessing mobile pollinator assemblages in just part of their range, mean that complementary studies in different cities and urban habitats are required to discover if these findings are more widely applicable.

Plant diversity and composition compensate for negative effects of urbanization on foraging bumble bees

“…As plant species diversity decreased with decreasing distance from the city's central point, our results confirm a negative effect of urbanization on plant species diversity and thus bumble bees, which agrees with previous studies (Ahrné et al 2009;Bates et al 2011;Banaszak-Cibicka and Żmihorski 2012;Jha and Kremen 2013b;Aronson et al 2014), but indicates that floral richness and composition, not urbanization per se, determine the presence of bumble bee foragers in small cities, such as Lüneburg.…”

“…One frequently discussed cause for the observed decline is habitat alteration and loss, especially through intensified farming (Fischer and Lindenmayer 2007;Goulson et al 2008b;Bommarco et al 2010;Pellissier et al 2013) and increasing urbanization (Ahrné et al 2009;Kearns and Oliveras 2009;Bates et al 2011;Geslin et al 2013). In many European countries, up to 80 % of the population lives in cities with urbanization further increasing (Antrop 2004).…”

Revealing the hidden niches of cryptic bumblebees in Great Britain: Implications for conservation

“…The south-east of England is also highly urbanised. Urban areas can support diverse pollinator assemblages but they can also have negative impacts on pollinator species (Bates et al, 2011). One obvious outlier in the distributions of both B. cryptarum and B. magnus is the Birch Tor site on Dartmoor in the south-west of England (Fig.…”

Variability of bumblebee communities (Apidae, Bombini) in urban green areas

“…In the mosaic environment of a big city the attractiveness of green spaces should also be determined by their areas. So far, this relationship has not been strictly defined (Hatfield and LeBuhn 2007;Bates et al 2011).…”