Data from: Pollination deficits increase with urbanization in Chicago

Urban 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 degrade them. The influence of urbanization on the pollination of
urban plants is even less understood. Urban agriculture relies on
plant-pollinator interactions for crop production, providing a relevant
framework to study pollination in an urban context. We therefore grew 240
plants across six sites at varying levels of urbanization in Chicago,
Illinois, to investigate how urbanization relates to 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 limitation experiment to test whether the
reproduction 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 surrounding impervious surface around each
site). We also examined how pollinator visitation rates vary with
urbanization. In S. lycopersicum but not C. pepo, the pollen addition
treatment had a consistent and significant positive effect on reproductive
success, indicating that plants of S. lycopersicum are pollen-limited in
our study area. The magnitude of this pollen limitation (the difference in
fruit set between paired control and pollen-supplemented plants) increased
with greater impervious surface, illustrating that S. lycopersicum plants
at more urban sites are more pollen-limited. The limited evidence for
pollen limitation in the more generalized C. pepo suggests that plants
with more specialized pollination systems are subject to greater pollen
limitation in urban environments. Together, our results demonstrate that
urban plants 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.