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Description

<b>Abstract</b><br/>

As cities around the world expand, we urgently need to better understand the drivers of urban biodiversity, especially for functionally important groups such as insect pollinators. In this study, we gathered hoverfly and bumble bee pollinator observations from natural history collections and community science initiatives from 462 urban landscapes across 85 U.S. metropolitan areas. We tested whether urban greenspace functions as pollinator habitat by examining whether the total area of greenspace in an urban landscape predicted pollinator occurrence, i.e., the presence or absence of species in a landscape. Our study was designed to determine whether there were differences between natural greenspace area (i.e., urban greenbelts, nature reserves and forest/grassland fragments) and developed greenspace area (i.e., managed parks, cemeteries and golf courses) in their ability to support a diversity of pollinator species. After accounting for sampling biases using an integrated occupancy modeling approach, we found a positive association between native hoverfly occurrence and natural greenspace area. This implies that urban landscapes with more natural greenspace support higher native hoverfly diversity. On average, bumble bee occurrence was not associated with natural greenspace area, however, the response varied among species, with several at-risk bumble bees showing a positive association. In contrast to natural greenspace area, we found no association between pollinator occurrence and the area of developed greenspace. In addition, we found that the proportion of racial minority households in an urban landscape was negatively associated with pollinator occurrence. This is consistent with the hypothesis that a history of systematic, unjust policies in neighborhoods with more racial minority households has lasting negative impacts on urban biodiversity. In conclusion, our results support the hypothesis that natural greenspace functions as vital habitat for urban pollinators. We recommend that cities prioritize the preservation of remnant natural greenspace and improve developed greenspaces in order to promote urban pollinator conservation. These efforts should be prioritized in urban landscapes with a higher proportion of racial minority households to improve equal access to nature and pollinator ecosystem services.</p>; <b>Methods</b><br />

In this study, we used publicly available data on urban land cover and urban socioeconomics and estimated their associations with urban pollinator occurrence rate. The publicly available urban land coverand urban socioeconomic data are large (continental scale) spatial files. The orginial sources for the spatial land cover and socioeconomic data are cited in the manuscript. We provide the site-specific land cover and socioeconomic predictor values that were derived from the publicly accessible data in a table - "site_data.csv". We focused on two groups of pollinator species - hoverflies (family Syrphidae) and bumble bees (family Apidae, genus <em>Bombus</em>). Pollinator detections were obtained from GBIF for hoverflies, and from the Bumble Bees of North America Database for bumble bees. The GBIF data request is cited in the README and in the manuscript text. The full Bumble Bees of North America Database data set is available upon request from the original provider, also cited in the README and in the manuscript text. </p>

We used integrated community occupancy models to quantify the associations between urban landscape predictors and urban pollinator occurrence. This model form estimates and accounts for detection biases in the data while simultaneously estimating associations with whether or not species occur. We looked at whether four focal predictrs were associated with occurrence: natural greenspace, developed greenspace, household income and neighborhood racial composition. Natural greenspace versus developed greenspacewere synthetic categories that we constructed based on the categorical land cover raster values provided by the original source. The integrated community occupancy models estimates community average associations with each of the four focal predictors. The effect of natural greenspace was our primary interest so we also estimated species-specific effects of the natural greenspace area on occurrence. We did not estimate species-specific effects for all four predictors because those more complex models failed to converge given the amount of data in our study. </p>