Study Species and Field Sampling
The four species of Clarkia in this study are sympatric in the
Kern River Canyon in Kern County, California. To determine if pollinator
foraging behaviors are reflected in the contents of their pollen balls,
we collected bees visiting Clarkia from May-June of 2014. We
sampled bees in 14 Clarkia communities throughout the four
species’ range of sympatry (Figure 1). Clarkia communities varied
in Clarkia species richness, and contained either one, two, or
four species of Clarkia (Table 1). In each community, we placed
four, 20m transects through patches of Clarkia . We sampled all
transects in all communities between 15 May and 15 June. Each community
was sampled twice on different days: once in the morning (between 8AM
and 12PM) and once in the afternoon (between 1PM and 3:30PM). Sampling
entailed walking along each transect for 20 minutes and catching bees
using a sweep net when they landed on Clarkia. Bees were
sacrificed using ammonium carbonate, and we noted the location, date,
and Clarkia species bees were visiting when we caught them. We
stored, pinned, and identified bee samples to species (or in the absence
of species-level resolution, to genus) using Michener et al. (1994). We
then scraped the pollen contents off of all collected bees and stored
each pollen ball in 90% ethanol in centrifuge tubes at -20°C.
At the end of every netting period, we surveyed Clarkia floral
abundance to estimate the relative abundance of each species. To do so,
we placed ½m2 quadrats every four meters on either
side of transects and counted all open flowers inside the quadrats.
Relative abundance of each species was calculated as the proportion of
the number of flowers that were open, divided by the total number of
flowers we counted at the survey time.
In the summers of 2015 and 2016, we also collected pollen from each
species of Clarkia for use in testing our methodological design.
To do so, we collected mature anthers from all four species ofClarkia in various communities throughout their range of overlap.
We removed pollen from the anthers and stored them in the same manner
that we stored pollen ball samples.