Pollination Services to Impatiens capensis (Balsaminaceae) Are Maintained across an Urbanization Gradient

Abstract

Premise of research. Urbanization is associated with the fragmentation of natural habitats, a reduction in agricultural pesticides, and high numbers of introduced species. Urbanization has also been connected to declines in native biodiversity, including of important ecosystem service providers such as pollinators. We expected that reported patterns of lower pollinator diversity and abundance in highly built-up urban areas should translate into higher pollen limitation of plant reproduction.Methodology. We set up arrays of 20 pots containing the native plant Impatiens capensis in 15 community gardens around the city of Ottawa, Ontario, Canada, that were selected to span a gradient of urbanization (defined as the percentage of surface area in a 100-m radius that was covered by pavement, buildings, or other impermeable surfaces). We collected data on the pollen limitation, lifetime fitness, and investment in selfed versus outcrossed reproduction over the course of each plant’s life span.Pivotal results. The plants in our study were pollen limited on average, but there was no association between the extent of pollen limitation and site urbanization. This result was robust to the landscape scale at which urbanization was calculated. In fact, the pollen limitation of our plants was similar to what has been reported in studies of I. capensis in the wild. Plant investment in selfing was not associated with urbanization; however, hand-pollinated plants in our study tended to invest more in outcrossed reproduction than open-pollinated plants, highlighting the mating system plasticity of this species.Conclusions. Our findings indicate that, for a plant that is native to this area, pollen limitation was not consistently higher in heavily built-up urban areas. We frame our findings in terms of new studies reporting the complexity of the impacts of urbanization on pollinators and their ecosystem services.