Field observation
Observations of plant phenology and flower-visiting insects were
conducted five times each year; on 26–30 May (term 1), 21–23 June
(term 2), 13–15 July (term 3), 7–9 August (term 4), and 28–30 August
(term 5) in 2017; on 5–8 June (term 1), 29 June (term 2), 29–31 July
(term 3), 13–14 August (term 4), and 3–5 September (term 5) in 2018.
Air temperature was measured at 1-hr intervals at the height of 1 m
above ground using a Tidvit V2 data logger (Hobo, Onset Co., USA) from
May 31, 2017 to September 3, 2018 at 3060 m elevation.
For the survey of flowering occurrence and flower production, 21 fixed
plots (named TW01-21; 2 × 10 m in size) were established at various
habitats (from dry ridge habitat to wet depression habitat) to cover the
whole vegetation types in the study site (Fig. S1). In each plot,
flowering occurrence and flower number of each species were recorded in
the early (term 1), middle (term 3), and late seasons (term 5).
Locations of individual plots were illustrated in Figure S1. In total,
flower productions of 81 species were recorded across plots during two
years. Furthermore, a phenological survey of flowering occurrence was
conducted for all entomophilous plant species in this area. In each term
(term 1–5), we walked around the whole area in which fixed plots were
set (within a 2.5 × 1.0 km area), and recorded flowering species. In
total, flowering phenologies of 130 species were recorded throughout the
survey periods.
For the survey of flower-visiting insects, we repeated 30-min censuses
of flower visitors by walk throughout the season (five terms). The
census period in each term was 1–3 continuous days during which 11–30
sets of census were conducted. Each census was conducted on calm days
(wind speed was < 4 m/s) during the daytime (8:00–17:00). In
total, 106 censuses (53 hrs.) and 102 censuses (51 hrs.) were conducted
in 2017 and 2018, respectively. At the beginning of each census, air
temperature and relative humidity were measured. Flower-visiting insects
were classified into following groups; (1) hymenopteran insects
(subdivided into bumble bee, honey bee, solitary bee, wasp, and sawfly),
(2) dipteran insects (syrphid fly, dagger fly, other fly), (3)
lepidopteran insects (butterfly, skipper, moth), (4) coleopteran
insects, (5) hemipteran insects, and (6) other insects. Ants and
grasshoppers were excluded from the observation because their activity
as pollinators seemed to be small. The number of insects visiting
flowers and plant species of the flowers were recorded. In total, visits
of 15,127 insects were recorded on the flowers of 105 plant species.
About 93% of observed insects were hymenopteran or dipteran insects
(see Results). Based on the composition of visiting insects, the
pollination type of individual plant species was classified into the
following five groups: (1) bee specialist: > 75% of
visitors are hymenopteran insects, (2) fly specialist: >
75% of visitors are dipteran insects, (3) bee generalist: 50–75% of
visitors are hymenopteran insects, (4) fly generalist: 50–75% of
visitors are dipteran insects, and (5) unclear type: very low visits
(< 5 visits) or mixture of several insect groups. In the
present study, both bee-specialist and bee-generalist species are
categorized as bee-visited species, and both fly-specialist and
fly-generalist species are done as fly-visited species.