Selection on floral traits in Primula farinosa

Abstract: Flowers and inflorescences have evolved in relation to animals for at least 100 million years. Plants attract pollinators with large, conspicuous, bright-coloured or scented flowers. These display attributes, however, also attract herbivores. Optimal conspicuousness may therefore represent a trade-off between attractiveness to pollinators and vulnerability to herbivores. In a heterogenic landscape, the abundances of pollinators and herbivores vary, and this variation should cause the local net selection on floral traits to vary as well. This thesis investigates how pollinators and herbivores select for floral traits, how this selection is linked to interaction intensities, and what factors determine spatial variation in interaction intensity. I have studied the small perennial herb, Primula farinosa, and its interactions with pollinators, a seed predator moth, and grazers. The plant varies in several floral traits; most notably it displays a polymorphism in scape length. Results showed that pollinators selected for long scape, while the seed predator and grazers selected against long scape. Local net selection on scape length depended on interaction intensities of all three interactions. Scape morph also affected selection on number and size of flowers. We hypothesised that intensity of seed predation should depend on local population history of the specialised moth. However, the results from a 5-year survey suggests that patches were recolonized every year, and that the most important patch choice criteria were plant characteristics, such as mean inflorescence size and scape morph frequency. Within a geographic selection mosaic, local hot spots of plant evolution may not be random patches, but patches chosen by the agent of selection based on plant trait values. This thesis shows how spatial population ecology and herbivore dispersal behaviour are linked to mosaic interactions and trait evolution.