Flowering phenology and flower production of alpine plants
There are many studies on the flowering phenology in alpine plant
communities (e.g., Holway & Ward, 1965; Thórhallsdóttir, 1998; Molau et
al., 2005; Jabis et al., 2020), and some of them focused on the
relationship between plants and flower visitors (e.g., Bosch et al.,
1997; Makolaos et al., 2008; Iler et al., 2013; Pelayo et al., 2019,
2021). However, comparative studies of flowering patterns between
different pollination types are limited as mentioned before (Kudo, 2016;
Mizunaga & Kudo, 2017). In the present study, the number of blooming
bee-visited species was positively related to the seasonal dynamics of
bee abundance, but there was no correlation between the number of
blooming fly-visited species and fly abundance. This difference may
reflect the temporal availability of pollinators for bee-visited and
fly-visited plants. A long-term study on the flowering phenology and
pollination success of Japanese alpine plants (Kudo, 2022) demonstrated
that the fruit-set rates of bee-visited plants increased as the season
progressed, reflecting the increasing pollination service by worker
bees. In contrast, the seasonal trend in the pollination success of
fly-visited plants was less clear, where the variations in fruit-set
success among species and between years were independent of flowering
time. This result indicates a small seasonal restriction of pollination
service by flies in alpine plant communities. Although the pollination
efficiency of flies was generally lower than that of bees (Herrera,
1987), frequent visits of fly pollinators might compensate for the low
efficiency per visit (Kearns & Inouye, 1994; Mizunaga & Kudo, 2017).
Also in the present study, the visitation frequency of dipteran insects
was 2.5 times larger than that of hymenopteran insects.
The seasonal patterns of flower production also differed between
bee-visited plants and fly-visited plants. Similarly in the Japanese
alpine communities, the seasonal pattern of flower production was
moderate in fly-visited plants, whereas flower production of bee-visited
plants tended to be maximum in the middle of the season although actual
flower production of bee-visited plants highly fluctuated from year to
year (Kudo, 2016; Mizunaga & Kudo, 2017). Interestingly, a recent
dataset of flower color diversity among 727 species (ca. 20% of Taiwan
flora) sampled along elevational gradient of Taiwan also found evidences
that the majority of Taiwan flora evolved to match bee’s innate color
preference (Tai et al., 2020). In particular, the floral color
diversities of bee-visiting plants in high altitude are over-dispersed
among related species perhaps to facilitate their co-existence (Tai et
al., 2020). Together, our data and the previous finding suggest the
bee-visited plants in alpine Taiwan may have shifted their flowering
times and colors to encourage bees’ visiting. These results suggest that
the flowering structure of alpine plant communities, i.e., temporal
dynamics of floral diversity and floral resources, may be influenced by
the relative composition of bee-visited and fly-visited species.