Bimodal activity of diurnal flower visitation at high elevation

Successful pollination in animal-pollinated plants depends on the temporal
overlap between flower presentation and pollinator foraging activity.
Variation in the temporal dimension of plant-pollinator networks has been
investigated intensely across flowering seasons. However, over the course
of a day, the dynamics of plant-pollinator interactions may vary strongly
due environmental fluctuations. It is usually assumed there is a unimodal,
diurnal, activity pattern, while alternative multi-modal types of activity
patterns are often neglected and deserve greater investigation. Here, we
quantified the daily activity pattern of flower visitors in two different
habitats contrasting high elevation meadows versus forests in Southwest
China to investigate the role of abiotic conditions in the temporal
dynamics of plant-pollinator interactions. We examined diurnal activity
patterns for the entire pollinator community. Pollinator groups may differ
in their ability to adapt to habitats and abiotic conditions, which might
be displayed in their patterns of activity. We hypothesized, that 1)
pollinator communities show multi-modal activity patterns, 2) patterns
differ between pollinator groups and habitat types, and 3) abiotic
conditions explain observed activity patterns. In total, we collected 4988
flower visitors belonging to six functional groups. There was a bimodal
activity pattern when looking at the entire pollinator community, and in
five out of six flower visitor groups (exempting solitary bees).
Bumblebees, honeybees, dipterans, lepidopterans, and other insects showed
activity peaks in the morning and afternoon, whereas solitary bees were
most active at midday. Activity of all six pollinator groups increased as
solar radiation increased and then decreased after reaching a certain
threshold. Our findings suggest that in habitats at higher elevations, a
bimodal activity pattern of flower visitation is commonly employed across
most pollinator groups that are diurnal foragers. This pattern may be
caused by insects avoiding overheating due to elevated temperatures when
exposed to high solar radiation at midday.