Attractiveness of floral traits to diverse pollinators in zygomorphic flowers of Isodon trichocarpus (Lamiaceae)

Abstract

When the abundance and the composition of pollinators are unpredictable, exploitation of a diverse assemblage of pollinators is important for plant reproduction. To examine the role of floral traits in attracting diverse pollinators, we performed a field study using the zygomorphic flowers of Isodon trichocarpus. We investigated variation in floral traits among flowers and seasonal variation in pollinator assemblage and determined whether pollinator behaviour is linked to floral traits. We compared pollinator diversity among flowers by flower-based rarefaction and extrapolation. Pollinator diversity increased with span of corolla opening. The number of bumble bee visits increased with upper lip height. During the flowering period, there were only 2 days when all pollinator groups (wasps, bumble bees, small bees and hoverflies) were observed, and there were 4 days when only one group was observed. Thus, the degree of generalization was not similar for all flowers because pollinator visits differed according to floral traits and some pollinator groups were observed in only part of the flowering season. Our results show that floral form increased attractiveness to diverse pollinators and that different flower traits were associated with different pollinator visits. Thus, pollinator assemblage in this species is related to floral traits.