Resource availability
To quantify the resources available to bees, we performed monthly field
surveys at each site, except for the July survey at site 1 that was
missed. We established five 100 x 2 meter transects along the edges of
experimental crop plantings or in fallow fields within 500 meters of the
hives at each site, for a total of 15 transects per survey period over
the three sites. One exception to the 500m distance was one transect at
site three which, due to measurement error, was placed 600 meters from
the hives. Each transect was subsampled using ten 1-meter diameter
circular quadrats. In each quadrat, we counted the number of individuals
of each plant species. To estimate floral abundance, we counted either
the number of flowers in a quadrat for plant species with non-clustered
flowers (e.g. Caryophyllaceae) or the number of racemes (e.g. Fabaceae)
or heads (e.g. Asteraceae) for plant species with clustered flowers.
Because the absence of a plant species in a quadrat resulted in many
zero counts, we estimated plant richness and diversity at the transect
rather than the quadrat level. Plant richness and diversity were
calculated at the levels of plant species and family, along with
morphotype to align with pollen identification. Diversity was calculated
using the Simpson D Index as described above for bee-collected pollen.
The same categories established for pollen morphotypes in pollen pellets
were used for plant resource morphotypes based on their pollen
morphology (Table 2). We determined the impact of site and survey period
on plant richness and diversity using a linear mixed model (proc mixed,
SAS v. 9.4) with site and survey period as fixed effects, and their
interaction as a random effect. A transect was the replicate in the
model, and the fixed effects were tested against the two-way interaction
error term.