Abstract
While urban beekeeping is on the rise, data on the role of wild bee communities as crop pollinators in cities is still scarce. We analysed wild bee visitation rates on apple, plum, cherry, pear, blackberry, raspberry, and strawberry in a Bavarian city with a very high honeybee density of c. 19 hives/km2. During 137.5 hours of observation time, we observed 52 wild bee species on the studied crop plants. During more than 50 h of observation time on fruit trees in flower, we found that wild bees provided 41% of the total bee visits, honeybees the remaining 59%. Honeybee hive density had a significantly negative effect on wild bee abundance. Bumblebees appeared more tolerant to poor weather conditions than all other bee groups. Wild bee species richness on apple flowers was not significantly impacted by flower diversity in the surroundings of the trees. Together, our results suggest that species-rich wild bee communities in urban areas are important for pollination success in common fruit crops, especially under unstable spring weather conditions. Bee-friendly management of urban spaces should be prioritised to support wild bee communities as well as the increasing number of honeybees in cities.
Highlights
Recent studies highlight the importance of urban agriculture for food security (Edmondson et al 2020), positive effects of urban agriculture on biodiversity in general (Lin et al 2015), and on bee species diversity in particular (Normandin et al 2017; Baldock et al 2019; Lanner et al 2020)
The number of small solitary bees was highest on berry flowers, the number of bumblebees and large solitary bee species was highest on apple flowers (Figure 4)
We show that wild bee visitation rate on orchard crops was negatively correlated to honey bee hive densities, which is in line with previous studies in natural habitats, agroecosystems and urban environments (TornéNoguera et al 2016; Alomar et al 2018; Ropars et al 2019; Renner et al 2021)
Summary
Recent studies highlight the importance of urban agriculture for food security (Edmondson et al 2020), positive effects of urban agriculture on biodiversity in general (Lin et al 2015), and on bee species diversity in particular (Normandin et al 2017; Baldock et al 2019; Lanner et al 2020). Despite increasing interest in bee diversity and conservation potential of urban habitats (Hernandez et al 2009; Baldock et al 2015; Hall et al 2017; Baldock 2020; Krahner & Greil 2020) much less attention has been directed towards pollination services in urban environments. This is Importance of wild bee communities as urban pollinators somewhat worrying since e.g., a survey of community gardens in New York City found that 92% of the crops require bee pollination to some degree to set fruit or seed (Matteson & Langellotto 2009). In one of the rare studies on urban food crop pollinators, Lowenstein et al (2015) found cucumber (Cucumis sativus), eggplant (Solanum melongena) and purple coneflower (Echinacea purpurea) in gardens in Chicago to be visited by different groups of pollinators with honeybees constituting less than 7% of visits, and fruit and seed set to increase with pollinator visitation and taxonomic richness
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