Patterns and mechanisms of temporal resource partitioning among bee species visiting basil (Ocimum basilicum) flowers

The way in which flower visitors share floral resources or compete for them throughout the day is a decisive factor for the effectiveness of pollination. We described daily rhythms of flower visitation by bee species and tested whether such patterns depend on: (1) the body size of the species, (2) the daily patterns of variation in weather and nectar standing crop, and (3) the effects of weather on the daily rhythm of variation in nectar standing crop. After 1 year of biweekly samplings, we encountered 56 bee species visiting basil flowers. Larger bee species were more active in the cooler and more humid hours of the morning. Smaller species foraged later, during the warmer and drier hours. Throughout the day, nectar volume decreased. In the laboratory, we determined a positive effect of increase in temperature on nectar volume, unlike the negative correlation recorded in the field. Nectar volume decreased in plants under experimental drought, showing similarity with the driest hours of the day. The daily cycle of temperature is the fundamental factor that, directly and indirectly, via air humidity, soil moisture, and nectar supply, influences bee activity according to body size and physiological attributes. In the field, the positive effect of increasing temperatures on nectar volume is masked by a stronger, negative effect of decreasing air humidity and soil moisture throughout the day.