Plant diversity and origin do not predict abundance and diversity of syrphid flies (Diptera: Syrphidae) in small urban gardens

Abstract Gardens have emerged as a key habitat resource for pollinators in cities, but more research is needed to determine the optimal garden characteristics for maximising native pollinator diversity. Syrphid flies (Diptera: Syrphidae) are abundant generalist fly pollinators that have received less study than other pollinators in urban gardens. In this study, we investigated whether flowering plant diversity and the presence of native plants were related to syrphid abundance and diversity in urban street gardens. Over a two-month period, we sampled 12 small public gardens in a residential urban area (Vancouver, British Columbia, Canada) to explore correlations between plant and syrphid assemblages. Gardens reflected the relative scarcity of native plants in our study system, such that gardens with native flowers present ranged from 10 to 60% cover. Although syrphid abundance and richness varied among gardens, neither floral richness nor the presence of native flowers was correlated with syrphid abundance or diversity. Beyond plant diversity and origin, other characteristics may be more important to syrphid visitation at the garden scale. A better understanding of the role of garden characteristics among the complex factors shaping urban syrphid assemblages will offer valuable insights for the improvement of pollinator conservation strategies.