Responses of hover fly diversity and abundance to urbanisation and local attributes of urban greenspaces

Abstract

Urban greenspaces are vital refugia for insect biodiversity, but seasonal fluctuation responses of insect taxa to urbanisation and local attributes of urban greenspaces are not well known. Regions with mild temperate climates and winter-flowering plants have active winter pollinators that are often neglected. A thorough knowledge of the seasonally fluctuating ecological needs of insects is essential for adequate insect-friendly greenspace management. Hover flies are cosmopolitan inhabitants of urban greenspaces where they provide multiple critical ecosystem services such as pollination and pest control. Our study uses a multi-scale approach to determine the seasonal effects of urbanisation on hover fly richness, abundance, and assemblages in urban greenspaces. We selected 30 sites along an urbanisation gradient (as measured by human population density) in Sydney, Australia, and sampled each site over a year across seasons. We found that hover fly species richness was higher in winter and spring than in summer, while abundance was highest in winter and lowest in summer. Our results also show that a combination urbanisation and local attributes of urban greenspaces (flower richness, flower abundance, human population density, and proportion of native flowers) combined to affect hover fly species richness and abundance in seasonally dependant ways. Hover flies are especially abundant and diverse during winter- a time of the year when other native floral visitors are less active. Thus, hover flies may be important pollinators of the large community of winter-flowering plants in Australia. Urban greenspaces can be made more hospitable to hover flies by implementing simple management initiatives, such as complementing native floral resources with non-native flowers in periods of scarcity.