Pollen collection and plant identity
Rates of pollen foraging were low on some days, and ultimately, we
collected 486 pollen pellets from bumble bees over 34 days, and 1048
from honey bees over 33 days (Appendix Table S1). Because no honey bee
pollen foragers were caught at site 1 during period 3, this site/period
combination was excluded from pollen analyses for honey bees. Over the
experiment, bees collected pollen from 20 distinct plant morphotypes and
16 plant families (Table 2). The morphotype classifications below family
included genus (e.g. Hemerocallis ) and species (e.g. Lotus
corniculatus ). When we could distinguish distinct pollen morphotypes
within a plant family but these morphotypes could not be accurately
associated with a genus or species, we subdivided the family using
defining features (e.g. Fabaceae_Tricolporate).
Over the flowering season, 65% of pollen returned to honey bee colonies
by foragers was from plants in the Fabaceae family, in contrast to
bumble bees who brought back 38% of pollen from Fabaceae, and 34% from
Brassicaceae (Fig. 1a). Furthermore, over both bee species, Fabaceae was
the most abundant pollen collected during all periods except for period
five, when Asteraceae became the most abundant (31.3%) plant family
along with Brassicaceae (26.2%), the latter being predominantly
collected by bumble bees (Fig. 1b).