Pollinator composition, visitation rates, and seed set in flower-color polymorphic populations of a cedar glade endemic, Nashville Breadroot (Pediomelum subacaule)

Abstract

Nashville Breadroot (Pediomelum subacaule) is a flowering plant endemic toCedar Glades of Northern Alabama, Northern Georgia, and Middle Tennessee. In middle Tennessee, populations of P. subacaule are characterized by a flower-color polymorphism in which individual plants produce exclusively purple or, very rarely, white flowers. The goal of this study was to test the hypothesis that the white flower variety suffers reduced fitness and is rare because of pollinator mediated selection. A series of field observation experiments was conducted to quantify pollinator composition, duration of pollinator visitation, and seed set in middle Tennessee populations of P. subacaule. My results suggest that flower color has a significant effect on pollinator preference, with different proportions of pollinator species visiting purple and white flowers (X2=26.9, df=3, p < 0.05). Statistical analysis also reveals that seed production by white-flowered plants is less than that of the purple flower variety (U = 12, p < 0.05). A statistical analysis was not conducted on times pollinators spent on white vs purple flowers, as visitation to the white flower variety was limited to a single individual of the focal pollinator community. Taken together, these results are consistent with the hypothesis that white flowered individuals are less attractive to key pollinator species, and therefore produce fewer seeds. Hence, the white-flowered morph may suffer a reduction in fitness, which may account for its persistent low frequency of occurrence in the populations studied.