The effects of urbanisation on pollinators and pollination: A meta-analysis

Urbanisation is increasing worldwide, with major impacts on biodiversity,
species interactions and ecosystem functioning. Pollination is an
ecosystem function vital for terrestrial ecosystems and food security;
however, the processes underlying the patterns of pollinator
diversity and the ecosystem services they provide in cities have seldom
been quantified. Here, we perform a comprehensive meta-analysis of 133
studies examining urbanisation effects on pollinator diversity and
pollination. Our results confirm the widespread negative impacts of
urbanisation on pollinator richness and abundance, with Lepidoptera being
the most affected group. Furthermore, pollinator responses were found to
be trait-specific, with below-ground nesting and solitary Hymenoptera and
spring flyers more severely affected by urbanisation. Meanwhile, cities
promote non-native pollinators, which may exacerbate conservation risks to
native species. Surprisingly, despite the negative effects of urbanisation
on pollinator diversity, pollination service measured as seed set is
enhanced in non-tropical cities likely due to abundant generalists and
managed pollinators therein. We emphasize that the richness of local
flowering plants could mitigate the negative impacts of urbanisation on
pollinator diversity. Overall, the results demonstrate the varying
magnitudes of multiple moderators on urban pollinators and pollination
service provision and could help guide conservation actions for
biodiversity and ecosystem function for a sustainable future.