Pollination in urban yards: Who's there and what socio-ecological variables affect visits to a mobile garden?

As vacant land in cities is repurposed for agricultural use, there is increasing interest in enhancing pollination services for production of wildflowers and crops. Anthropogenic changes within city boundaries result in finer scale interactions between bees and their floral hosts compared to rural-urban gradients. We studied pollination in an urban area by bringing a mobile garden, consisting of cucumber, eggplant, and purple coneflower plants, to thirty residential yards. We recorded bee visits to the mobile garden, the floral community in the surrounding yard, as well as the floral and pollinator communities on city blocks in front of sampled homes. After 72 hours in yards, plants were returned to a greenhouse, isolated from further pollinator visits, and grown until maturity. We measured the number of cucumbers and eggplants formed, the number of seeds produced, and the amount of shriveling in purple coneflower florets as calculations of pollination services. Purple coneflower plants attracted the greatest number of bee visits, and pollination in urban yards led to the formation of cucumber and eggplant fruits at nearly all sites. Greater floral abundance in yards led to more rapid bee recruitment and more visits to mobile gardens. Data from 2012 indicate increasing bee abundance in more densely populated neighborhoods, but we did not find a similar relationship for pollination services. Our results demonstrate the importance of ornamental flowers on residential property for urban bees and characteristics of urban neighborhoods that impact pollination.