Daily patterns of pollinator activity, differential pollinating effectiveness, and floral resource availabifity, flowering Mediterranean shrub

Abstract

This study examined the daily activity patterns of the pollinators of Lavandula latifolia (Labiatae), a summer-flowering, insect-pollinated evergreen shrub of Med­ iterranean woodlands. The question is addressed, What is the degree of matching between the daily floral cycle of L. latifolia and the daily profile of pollinating potential of its pollinator assemblage? L. latifolia open flowers and produce nectar uninterruptedly over daytime, and both flower production and nectar secretion rates are highest early in the morning and late in the afternoon. Pollen availability in the flower population, as estimated by the proportion of pollen-bearing, male-phase flowers, 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 (hymenopterans, dipterans, lepidopterans), 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 effectiveness, on the other. It is suggested that both the plant’s and the pollinators’ daily cycles largely represent independent responses to did rhythmicity of the phys­ ical environment, and that matches and mismatches found here between daily pat­ terns of floral resources and aspects of pollinating effectiveness are epiphenomena lacking particular adaptive significance to the plant.