UC Irvine

Animal pollination occurs in more than three quarters of all flowering plants. These plant-pollinator interactions can be greatly affected by the environment. The increasing presence of invasive species and changes to abiotic conditions could change the outcomes of plant-pollinator interactions. This dissertation focused on identifying how invasive plants and changes to water availability influence seed production and pollinator-mediated selection.

The first chapter demonstrated how water availability to pollen recipient plants (Phacelia parryi) as well as conspecific and heterospecific pollen (the invasive plant, Brassica nigra) donors interacted to influence seed production. In this experiment, water availability to recipient plants did not influenced seed production. High-water availability to conspecific pollen donors led to higher seed production. Water availability to heterospecific pollen donors set the context for how water given to conspecific donors and recipient plants impacted seed production. These results show the potential impacts that environmental heterogeneity has on post-pollination events that lead to seed production.

The second chapter explored how water availability influences the shape of the relationship between seeds and pollen received. Water availability influenced the pollen-to-seed relationship and the degree to which seed production is limited by pollen quantity. Data for chapters one and two were collected through a series of hand-pollination experiments done in a pollinator-free greenhouse.

The third chapter documented the impacts that the presence of an invasive plant (Linaria vulgaris) across years had on pollinator visitation and pollinator-mediated selection on floral traits in a native plant species (Penstemon strictus). This was done through a multi-year field experiment in Colorado, USA. The presence of Linaria increased pollinator visits to Penstemon. Both pollinator preferences and the relationship between pollinator visits and seed production changed across years.

Together, this work documents two previously-unknown mechanisms on how seed production can be influenced by water to pollen donors and to a change in the pollen-to-seed relationship. This work also illustrates how year-to-year variation in plant-pollinator interactions and the presence of a plant invader affects pollinator visitation and pollinator-mediated phenotypic selection.