Constancy
Of the 150 pollen balls we analyzed, 21 out of 150 bees (14%) were
caught on Clarkia flowers that were different from the majority
of the Clarkia pollen found in their pollen balls, indicating at
least some amount of pollinator inconstancy (Figure 3). The contents of
the pollen balls, however, indicate that pollinators were often
constant. This includes a caveat: the final measurement of RRA with no
cutoff returned all four species of Clarkia in 100% of the
samples, indicating the unlikely result that all pollinators are not
only inconstant, but visited all four Clarkia species - even when
collected in communities containing fewer than four Clarkiaspecies. Not only is this result unlikely based on the biology of the
system, but it is exceedingly rare that any quantitative analysis with
relative read abundance would use raw read count in the analysis. As
such, the rest of our results will compare RRA with 5% (RRA5) and 10%
(RRA10) cutoffs with qAMPseq.
In the large majority of samples, pollen balls contained only one
species of Clarkia pollen. Estimates of single-species pollen
balls varied among methods, with 66% (RRA5), 74% (RRA10), or 76%
(qAMPseq) of samples containing only one Clarkia species. This
indicated a striking level of constancy, emphasized by the fact that
70% of bees we sampled were captured in multi-species Clarkiacommunities. Furthermore, the Pearson’s Chi-squared test comparing the
number of bees from communities with one to four floweringClarkia species versus the number of pollen samples with one to
four flowering Clarkia species was significant
(X2 (3)=77.05, p<0.001), confirming that
even in diverse Clarkia communities, bees were constant (Figure
4, Panel B; Table 2).
Despite overall pollinator constancy, a quarter (qAMPseq, 24%; RRA10,
26%) to a third (RRA5, 33%) of the bees were inconstant, often
carrying two species of Clarkia pollen. The most common
multi-species combination in pollen balls was C. cylindrica andC. unguiculata (Figure 3). No pollen balls contained all four
species of Clarkia . Bees carrying C. speciosa pollen - the
most behaviorally specialized of the Clarkia (James 2020) -
tended to only carry C. speciosa pollen: when present, C.
speciosa was the only species of pollen in the pollen ball in 12/14
cases. Bees carrying the other three species of Clarkia often
carried mixtures of the three (Figure 3).
Relative abundance measurements of Clarkia in pollen balls were
largely the same between qAMPseq, RRA5, and RRA10, and most similar
between qAMPseq and RRA10 measurement methods (Table 2 and Figure 4;
Panel B).