Urban Ecosystems If you plant it, they will come: quantifying attractiveness of crop plants for winter-active flower visitors in community gardens --Manuscript Draft-- Manuscript Number: UECO-D-19-00111 Full Title: If you plant it, they will come: quantifying attractiveness of crop plants for winter-active flower visitors in community gardens Article Type: Manuscript Keywords: winter pollination; urban conservation; visitor network; urban garden; urban ecology; pollinators; Syrphidae; Hymenoptera Corresponding Author: Tanya Latty University of Sydney Eveleigh, NSW AUSTRALIA Corresponding Author Secondary Information: Corresponding Author's Institution: University of Sydney Corresponding Author's Secondary Institution: First Author: Perrin Tasker First Author Secondary Information: Order of Authors: Perrin Tasker Chris Reid Andrew D. Young Caragh G Threlfall Tanya Latty Order of Authors Secondary Information: Funding Information: Abstract: Urban community gardens are potentially important sites for urban pollinator conservation because of their high density, diversity of flowering plants, and low pesticide use (relative to agricultural spaces). Selective planting of attractive crop plants is a simple and cost-effective strategy for attracting flower visitors to urban green spaces, however, there is limited empirical data about which plants are most attractive. Here, we identified key plant species that were important for supporting flower visitors using a network-based approach that combined metrics of flower visitor abundance and diversity on different crop species. We included a metric of ‘popularity’ which assessed how frequently a particular crop plant appeared within community garden. We also determined the impact of garden characteristics such as size, flower species richness, and flower species density on the abundance and diversity of flower visitors. We found two plant species, Brassica rapa and Ocimum basilicum were identified as being key species for supporting flower visitor populations on all three of our metrics. Flower species richness had a strong positive effect on both the abundance and diversity of flower visitors. We suggest that gardeners can maximise the conservation value of their gardens by planting a wide variety of flowering plants including highly attractive plants such as B. rapa and O. basilicum. Suggested Reviewers: Katherine Baldock University of Bristol [email protected] Francis Ratnieks University of Sussex [email protected] Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation Mikhail Garbuzov University of Sussex [email protected] Ania Majewska University of Georgia [email protected] Ken Thomson University of Sussex [email protected] Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation Manuscript Click here to download Manuscript Tasker et al for UE 25 April.docx Click here to view linked References 1 If you plant it, they will come: quantifying attractiveness of crop plants for winter-active 2 3 flower visitors in community gardens 4 5 6 1 2 4, 5 1, 3 1 7 Perrin Tasker , Chris Reid Andrew D. Young , Caragh G Threlfall Tanya Latty 8 9 1. School of Life and Environmental Sciences, University of Sydney, Sydney, NSW 2006, 10 11 Australia 12 13 1. Department of Biological Sciences, Macquarie University, Sydney, NSW 2109, 14 Australia 15 2. School of Ecosystem & Forest Sciences, The University of Melbourne, Parkville, VIC 16 17 3010 18 3. Plant Pest Diagnostics Center, California Department of Food and Agriculture, 3294 19 Meadowview Road, Sacramento, CA 95832, USA 20 21 4. Department of Entomology and Nematology, UC Davis, Briggs Hall, Davis, CA 95616- 22 5270, USA 23 24 25 26 Corresponding author: Tanya Latty: [email protected] 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 1 63 64 65 Abstract 1 Urban community gardens are potentially important sites for urban pollinator conservation 2 3 4 because of their high density, diversity of flowering plants, and low pesticide use (relative to 5 6 7 agricultural spaces). Selective planting of attractive crop plants is a simple and cost-effective 8 9 strategy for attracting flower visitors to urban green spaces, however, there is limited 10 11 12 empirical data about which plants are most attractive. Here, we identified key plant species 13 14 that were important for supporting flower visitors using a network-based approach that 15 16 17 combined metrics of flower visitor abundance and diversity on different crop species. We 18 19 included a metric of ‘popularity’ which assessed how frequently a particular crop plant 20 21 22 appeared within community garden. We also determined the impact of garden 23 24 25 characteristics such as size, flower species richness, and flower species density on the 26 27 abundance and diversity of flower visitors. We found two plant species, Brassica rapa and 28 29 30 Ocimum basilicum were identified as being key species for supporting flower visitor 31 32 populations on all three of our metrics. Flower species richness had a strong positive effect 33 34 35 on both the abundance and diversity of flower visitors. We suggest that gardeners can 36 37 38 maximise the conservation value of their gardens by planting a wide variety of flowering 39 40 plants including highly attractive plants such as B. rapa and O. basilicum. 41 42 43 44 45 46 47 Keywords: winter pollination, urban conservation, visitor network, urban garden, urban 48 49 ecology, pollinators, Syrphidae, Hymenoptera 50 51 52 53 54 55 56 57 58 59 60 61 62 2 63 64 65 Introduction 1 Urbanisation is one of the major drivers of environmental change and has both direct 2 3 4 (habitat loss, land conversion) and indirect (heat island effect, changes in resource availability) 5 6 7 impacts on biodiversity. Given the pace of land conversion, developing strategies to conserve 8 9 biodiversity within cities is imperative. While conserving tracts of high-quality habitat (‘land 10 11 12 sparing’) is likely beneficial, it is largely not possible in the inner city where land changes are 13 14 largely irreversible. Enacting strategies that support target organisms within existing urban 15 16 17 land uses (‘land sharing’) by providing key resources may lead to better outcomes for 18 19 biodiversity in highly urbanised environments (Soga et al. 2014). 20 21 22 23 The increasing recognition of the conservation value of gardens within cities 24 25 (Baldock et al. 2019) coincides with interest in strategies for designing ‘pollinator friendly 26 27 28 gardens’ more broadly (Majewska and Altizer 2019). A large metanalysis of 178 studies found 29 30 31 that within-garden features such as flower diversity had a stronger impact on pollinator 32 33 populations than did landscape level features such as degree of urbanisation or distance to 34 35 36 agricultural fields(Majewska and Altizer 2019). (Kevin C Matteson & Langellotto, 2011) found 37 38 that the best predictors of bee and butterfly richness in US community gardens were floral 39 40 41 area and sunlight availability, while a study of domestic gardens in the UK identified native 42 43 plant species richness, the number of surrounding houses, and the extent of low canopy 44 45 46 vegetation as key drivers of solitary bee diversity (Smith, Warren, Thompson, & Gaston, 47 48 49 2006). In Australia, increases in the proportion of flowering native plants in a green space had 50 51 a positive impact on the density of non-native honey bees (Apis mellifera), while native, 52 53 54 ground dwelling Homalictus bees were most abundant in areas with low flower diversity and 55 56 small amounts of surrounding impervious surfaces (Threlfall et al. 2015). Taken together, 57 58 59 60 61 62 3 63 64 65 these studies suggest that flower communities are key to creating gardens that support strong 1 2 3 populations of flower-visiting insects. 4 5 6 Gardens are essentially constructed ecosystems, where the plant community is 7 8 explicitly selected and arranged by gardeners. This allows tremendous potential for selecting 9 10 11 plants that optimally support pollinators. Indeed, several studies of bees in urban gardens 12 13 14 have suggested (but not tested) that bee diversity may be largely attributable to the presence 15 16 or absence of particularly attractive flower species (Gunnarsson and Federsel 2014; Makinson 17 18 19 et al. 2017). 20 21 22 While there are many recommendations for choosing pollinator-friendly crop species, 23 24 25 the evidence base for flower selection is primarily anecdotal (Ratnieks and Garbuzov 2014). 26 27 Lists of pollinator friendly species available to the public often include poor 28 29 30 recommendations, a very large number of species, and are generally not based on empirical 31 32 data (Ratnieks and Garbuzov 2014; but see Garbuzov et al. 2017; Garbuzov and Ratnieks 2013; 33 34 35 Garbuzov et al. 2015 for exceptions). A notable exception is the experiment of (Garbuzov 36 37 38 and Ratnieks 2013) which investigated the relative attractiveness of 32 different plant species 39 40 in a specially planted pollinator garden. They found clear differences in plant attractiveness 41 42 43 and suggest that plant selection could be a powerful and cost effective strategy for making 44 45 gardens more pollinator-friendly. 46 47 48 49 Our primary aim in the present study was to identify pollinator-friendly plant species 50 51 that have the potential to attract pollinators to urban community gardens. We were also 52 53 54 interested in local-scale drivers of flower visitor abundance and diversity such as garden size, 55 56 flower density and flower abundance. Community gardens are becoming increasingly popular 57 58 59 in major cities around the world as people become more interested in local food production 60 61 62 4 63 64 65 and the social and health benefits of gardening (Guitart et al.