2.3 Flower visitor assemblages and size variation
To investigate the flower visitors of A. buergeriana var.buergeriana , we walked through each population and captured
insects that were visiting flowers. This survey was conducted during
7:00–14:00 local time, when flower visitors are active. Each population
was observed a total of 60–180 min over 1–3 days at the peak of the
flowering season. Captured insects were measured from the tip of the
proboscis to the end of the abdomen with a digital caliper (precision,
0.01 mm) to determine visitor size (Figure 1c). Observations were made
of visitors to both yellow and red flowers to confirm that there were no
differences in visitor assemblage or visiting frequency between
differently colored flowers.
As the average visitor size for each plant population, the weighted
arithmetic average was calculated from the relative abundance of each
visitor species and the size of that species:
\begin{equation}
Average\ visitor\ size=\ \sum_{i=1}^{n}{Pi(Ni/Nt)}\nonumber \\
\end{equation}where n = the total number of insect species visiting a A.
buergeriana var. buergeriana population, Pi = the average
size of the i th insect species, Ni = the number of flowers
in the population that the i th insect species visited, andNt = the number of flowers in the population that any of the
insect species visited. Thus, Ni /Nt is the relative
abundance of the i th insect species visiting the population.
Observations of flower visitor frequency showed that large bumblebees
(Bombus spp.) were the main visitors, although small bees
(Ceratina spp.) also visited occasionally. Bumblebees, which
extend their proboscis to the nectar source at the tip of the spur to
suck nectar, visited both male and female phases and both yellow and red
flowers (Toji personal observation). Smaller bees could not reach the
spur tip to forage for nectar. Furthermore, although they sometimes
collected pollen from the flowers, they did not contribute to
pollination because they rarely moved between plant individuals and did
not visit female-phase flowers. Because the pollen visitation patterns
of the bumblebees and small bee species were very different, we
calculated average visitor size for all visitors (i.e., bumblebees plus
small bees) and for bumblebees only.