Study species & sites
We conducted our experiment from June through October, 2021, using two plant species: Solanum lycopersicum var. “Sungold” (Solanaceae), sun gold tomatoes, and Cucurbita pepo var. “Jaune et Verte” (Cucurbitaceae), patty pan squash. These species are both agriculturally important crops that are readily grown on urban farms in Chicago, and each represents a unique pollination morphology and ecology. Solanum lycopersicum flowers have poricidal anthers, a specialized floral morphology in which pollen is released only by bee species capable of sonication, or “buzz”-pollination, such asBombus (Apidae), Xylocopa (Apidae), and Halictinae(Halictidae) species (Buchmann 1983). Cucurbita pepo are monoecious and have a unique relationship with squash bees,Peponapis and Xenoglossa species (Apidae), where female bees collect pollen exclusively from cucurbit flowers (Hurd et al. 1971). These bees appear to be the most efficient pollinators ofCucurbita species, however, the flowers are still visited and pollinated by a variety of generalist pollinators, including the widespread European honeybee, Apis mellifera (Canto-Aguilar and Parra-Tabla 2000, Serra and Campos 2010, McGrady et al. 2020, Kamo et al. 2022). Using these two species for our experiment provides insight into how pollination in urban environments differs between a specialized plant that is pollinated only by a small subset of local pollinators and a plant that relies on a more generalized suite of pollinators.
We worked with Windy City Harvest (WCH), an urban agriculture program through the Chicago Botanic Garden (CBG), to carry out our pollination experiment at five agricultural sites in Chicago, IL and one site at the CBG in suburban Glencoe, IL. Study plants at urban sites were placed within WCH urban farms, surrounded primarily by other crop species growing in raised beds, and plants at the suburban site were in a botanical garden setting, surrounded largely by ornamental plants and species native to Illinois, including a fruit and vegetable garden. Following Gruver and CaraDonna (2021), we quantified urbanization as the percent of impervious land cover surrounding each site within a 500 m radius and 1000 m radius, calculated using ArcGIS 10.7.1 and 2019 impervious cover data from the USGS National Landcover Database (Multi-Resolution Land Characteristics Consortium, mrlc.gov). Impervious surface ranged from 49.3% to 71.5% at 500 m and 57.0% to 77.9% at 1000 m across the urban farm sites. Impervious surface was 19.7% at 500 m and 32.1% at 1000 m at the CBG (Table 1, Fig. 1).