Understanding how urbanization alters functional interactions among
pollinators and plants is critically important given increasing
anthropogenic land use and declines in pollinator populations.
Pollinators often exhibit short-term specialization, and visit plants of
the same species during one foraging trip. This facilitates plant
receipt of conspecific pollen -- pollen on a pollinator that is the same
species as the plant on which the pollinator was foraging. Conspecific
pollen receipt facilitates plant reproductive success and is thus
important to plant and pollinator persistence. We investigated how
urbanization affects short term specialization of insect pollinators by
examining pollen loads on insects' bodies and identifying the number and
species of pollen grains on insects caught in urban habitat fragments
and natural areas. We then assessed possible drivers of differences
between urban and natural areas, including frequency dependence in
foraging, species richness and diversity of the plant and pollinator
communities, floral abundance, and the presence of invasive plant
species. Pollinators were more specialized in urban fragments than in
natural areas, despite no differences in the species richness of plant
communities across site types. These differences were likely driven by
higher specialization of common pollinators, which were more abundant in
urban sites. Pollinators were also more specialized when foraging on
invasive plants across sites, and floral abundance of invasive plants
was higher in urban sites. Our findings reveal strong effects of
urbanization on pollinator fidelity to individual plant species and have
implications for the maintenance of plant species diversity in small
habitat fragments. The higher fidelity of pollinators to invasive plants
suggests that native species may receive fewer visits by pollinators.
Therefore, native plant species diversity may decline in urban sites
without continued augmentation of urban flora or removal of invasive
species.