DAILY PATTERNS OF POLLINATOR ACTIVITY, DIFFERENTIAL POLLINATING EFFECTIVENESS, AND FLORAL RESOURCE AVAILABILITY, IN A SUMMER-FLOWERING MEDITERRANEAN SHRUB

Examined the daily activity patterns of the pollinators of Lavandula latifolia (Labiatae). Lavender open flowers and produce nectar uninterruptedly over daytime; both flower production and nectar secretion rates are highest early in the morning and late in the afternoon. Pollen availability in the flower population reaches a maximum in late afternoon, while nectar and sugar availability peak around the middle of the day. There was considerable variation both among major groups (Hymenoptera, Diptera, Lepidoptera), and among species within groups, in the timing of foraging at flowers. As a consequence of this, and of interspecific differences in pollen transfer effectiveness and average flight distance between consecutively visited flowers, the daytime period is not homogeneous with regard to the potential pollinating effectiveness of the pollinators active at a given time. There is not, however, a good correlation between the daily cycles of floral resource production and availability, on one hand, and of components of pollinating effectivness, on the other. Both the plant's and the pollinators' daily cycles probably largely represent independent responses to diel rhythmicity of the physical environment. Matches and mismatches found here between daily patterns of floral resources and aspects of pollinating effectiveness are epiphenomena lacking particular adaptive significance to the plant. -from Author