Results
Over thirteen weeks, we observed 116 pollinators across at least three
genera visiting S. lycopersicum and 330 pollinators across at
least five genera visiting C. pepo flowers. Of the visitors toS. lycopersicum , bees we could not identify to genus made up
55.7% of visits, followed by Bombus (40.2%), Agapostemon(2.4%), and Apis mellifera (1.7%). Squash bees (Peponapis
pruinosa) made up 54.8% of visits to C. pepo , followed by
insects we could not identify to genus (18.1%), European honeybees
(Apis mellifera ) (13.3%), and bees in the generaMelissodes (9.8%), Bombus (2.9%), and Agapostemon(1.1%).
Pollen limitation in S. lycopersicum increased with impervious
surface across all measures of reproduction: fruits per flower, seeds
per fruit, fruit mass, and fruit diameter (Table 3; Fig. 2-3). All four
reproductive measures were significantly pollen-limited across all
sites, except for fruit mass and diameter at our suburban site with the
least surrounding impervious surface (19.7%, Chicago Botanic Garden)
(Table 2, Fig. 2-3).
Across sites, the magnitude of pollen limitation in C. pepoincreased marginally with impervious surface for fruit set, but there
was no effect for seed set (Table 3; Fig. 4a). Cucurbita pepofruit set was not significantly pollen-limited at any of the six sites.
Seed set was significantly pollen-limited at one of the six sites, the
site with the highest level of impervious surface (77.2%, Kenneth)
(Table 2, Fig. 4b).
For S. lycopersicum , the rate of pollinator visitation decreased
with greater surrounding impervious surface
(R2m = 0.073, p = 0.015, estimate ± SE =
-0.023 ± 0.01; Figure 5a). The rate of visitation by Bombus spp.
did not relate to impervious surface (R2m =
0.052, p = 0.174, estimate ± SE = -0.019 ± 0.01; Figure 5c),
while visitation by small bees we could not identify to genus decreased
marginally with impervious surface (R2m =
0.089, p = 0.063, estimate ± SE = -0.026 ± 0.01; Figure 5e). In
contrast, the rate of visitation for C. pepo did not change
significantly with impervious surface (R2m =
0.007, p = 0.56, estimate ± SE = 0.007 ± 0.013; Figure 5b). The
rate of visitation by P. pruinosa increased marginally with
impervious surface (R2m = 0.148, p =
0.093, estimate ± SE = 0.049 ± 0.03; Figure 5d).