Wed, Aug 17, 2022: 11:00 AM-11:15 AM
516B
Background/Question/MethodsUrban growth is occurring rapidly, and the land use changes associated with urbanization may have consequences for pollinators and the plants that rely on them. Despite its importance in the face of pollinator declines and expanding urban ecosystems, our understanding of the effects of urbanization on pollination mutualisms is scant. There is both evidence that urban areas support diverse pollinator communities and evidence that they do not. The influence of urbanization on urban plant pollination is even less understood. Urban agriculture relies on plant-pollinator interactions, providing a relevant framework to study pollination in an urban context. We grew 240 plants across six agricultural sites at varying levels of urbanization in Chicago, Illinois, to investigate how urbanization relates to crop pollination of a generalized pollination system in Cucurbita pepo (squash) and a more specialized pollination system in the buzz-pollinated Solanum lycopersicum (tomato). We used a pollen addition experiment to ask whether the fruit production of plants at urban farms is pollen-limited, and whether the magnitude of pollen limitation varies with the extent of urbanization (quantified as the percent of impervious surface) around each site. We also examined how pollinator visitation rate varies with urbanization and influences reproduction.
Results/ConclusionsIn both Cucurbita pepo and Solanum lycopersicum, the pollen addition treatment had a significant positive effect on both fruit set and seed set, suggesting that plants of both species are pollen limited in our study area. In control plants, impervious surface was related to fruit set, where both C. pepo and S. lycopersicum plants generally produced fewer fruits per flower at more urban sites. Control plants produced fewer fruits per flower at sites with lower pollinator visitation rates, which also corresponded to more urban sites. The magnitude of pollen limitation (the difference in fruit set between paired control and pollen supplemented plants) increased with greater urbanization for both species. This trend suggests that plants at more urban sites are more pollen limited. The effect of pollen addition on fruit set was greater for S. lycopersicum than for C. pepo, which might indicate that plants with more specialized pollination systems are subject to greater pollen limitation in urban environments. Together, these results demonstrate that urban crops are likely experiencing deficits in pollination services, but in ways that vary with both the type of pollination system and the level of urbanization in the surrounding area.
Results/ConclusionsIn both Cucurbita pepo and Solanum lycopersicum, the pollen addition treatment had a significant positive effect on both fruit set and seed set, suggesting that plants of both species are pollen limited in our study area. In control plants, impervious surface was related to fruit set, where both C. pepo and S. lycopersicum plants generally produced fewer fruits per flower at more urban sites. Control plants produced fewer fruits per flower at sites with lower pollinator visitation rates, which also corresponded to more urban sites. The magnitude of pollen limitation (the difference in fruit set between paired control and pollen supplemented plants) increased with greater urbanization for both species. This trend suggests that plants at more urban sites are more pollen limited. The effect of pollen addition on fruit set was greater for S. lycopersicum than for C. pepo, which might indicate that plants with more specialized pollination systems are subject to greater pollen limitation in urban environments. Together, these results demonstrate that urban crops are likely experiencing deficits in pollination services, but in ways that vary with both the type of pollination system and the level of urbanization in the surrounding area.