MICROCLIMATE AND INDIVIDUAL VARIATION IN POLLINATORS - FLOWERING PLANTS ARE MORE THAN THEIR FLOWERS

Variation in pollinator composition at the individual plant level is a n important prerequisite for plant specialization on pollinators that does not seem to have been investigated previously. I studied variatio n in pollinator composition in a southeastern Spanish population of th e insect-pollinated shrub lavandula latifolia (Labiatae) and examined its correlates, with particular reference to the distinction between f actors intrinsic (flower morphology, nectar standing crop, size of flo ral display) and extrinsic (sunlight regime, ambient temperature, humi dity) to the plants. L. latifolia shrubs differed significantly in all intrinsic variables measured, in average irradiance levels (due to si te-dependent variation in timing and duration of insolation periods), and in pollinator composition at both the species and order levels. In dividual variation in pollinator composition was largely due to differ ences among insect taxa in their foraging responses to the sunlight mo saic. While some pollinators foraged indiscriminately over that mosaic , others preferred sites characterized by high irradiance. Variation a mong plants in intrinsic variables wan unrelated differences in pollin ator composition, which depended significantly only on the sunlight re gime associated with each plant's location in the habitat. Site-specif ic effects in pollination will generally act to reduce the likelihood of selective pressures by animals on plant traits. Their importance sh ould be greatest in habitats characterized by patchiness in environmen tal variables that affect pollinator behavior and in plants with polli nator assemblages dominated by ectothermic species.