Abstract
Insect pollinators provide a crucial ecosystem service, but are under threat. Urban areas could be important for pollinators, though their value relative to other habitats is poorly known. We compared pollinator communities using quantified flower-visitation networks in 36 sites (each 1 km2) in three landscapes: urban, farmland and nature reserves. Overall, flower-visitor abundance and species richness did not differ significantly between the three landscape types. Bee abundance did not differ between landscapes, but bee species richness was higher in urban areas than farmland. Hoverfly abundance was higher in farmland and nature reserves than urban sites, but species richness did not differ significantly. While urban pollinator assemblages were more homogeneous across space than those in farmland or nature reserves, there was no significant difference in the numbers of rarer species between the three landscapes. Network-level specialization was higher in farmland than urban sites. Relative to other habitats, urban visitors foraged from a greater number of plant species (higher generality) but also visited a lower proportion of available plant species (higher specialization), both possibly driven by higher urban plant richness. Urban areas are growing, and improving their value for pollinators should be part of any national strategy to conserve and restore pollinators.
Highlights
Animal pollination is essential for reproduction in many plant species [1,2] and has been valued globally at E153 billion p.a. (2005) [3] and at more than £510 million p.a. for UK crop production (2009) [4]
Similar numbers of visits were recorded to native and non-native plant species in urban sites; by contrast, almost all flower-visitors were recorded on native plant species in farmland and nature reserve sites. This is the first study to systematically compare pollinator communities in replicate urban and non-urban landscapes; it is based on highly resolved flower– visitor interaction networks
Our results show that while there was no difference in pollinator abundance and richness between urban, farmland and nature reserve sites, patterns varied between taxa
Summary
Animal pollination is essential for reproduction in many plant species [1,2] and has been valued globally at E153 billion p.a. (2005) [3] and at more than £510 million p.a. for UK crop production (2009) [4]. Animal pollination is essential for reproduction in many plant species [1,2] and has been valued globally at E153 billion p.a. Declines have been reported for all key insect pollinator groups, including honeybees, bumblebees, solitary bees and hoverflies [5,6,7,8]. Habitat loss and fragmentation (including urbanization), pesticides, pathogens and their interactions are all proposed drivers of pollinator decline [9,10]. Pollinators have been widely studied in agricultural systems and natural habitats, but urban areas remain under-studied and their suitability for pollinators is unclear. Urbanization represents a major proposed cause of insect decline [11], through alteration of ecological features important to pollinators, such as food and nesting sites [12,13]; many previous studies.
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