UC Irvine

Interactions between a native plant species and its pollinators, herbivores, or microbiome can be affected by the presence of non-native plant species. Non-native plant species are altering plant-pollinator interactions, yet we know little about how these non-native species influence natural selection. In addition, year-to-year variation in flowering could influence the impacts of non-native species on reproductive success in native plants and the strength and direction of pollinator-mediated selection. We examined whether the presence of the highly invasive plant Linaria vulgaris influenced average pollinator visitation, species composition of floral visitors, or pollinator-mediated selection in the native Penstemon strictus. In the field, we conducted small scale L. vulgaris inflorescence removals, that were repeated through 3 years. Pollinator-mediated selection on the floral trait of platform length was examined by determining the relationships between platform length and visitation, between visitation and seed production, and by calculating net selection based on seed production. We found that the presence of L. vulgaris on a small spatial scale facilitated pollinator visitation rates to P. strictus but did not influence pollinator-mediated selection on platform length. Pollinator visitation varied across years, as did the relationship between seed production and pollinator visitation, and the relationship between pollinator visitation and platform length. Although components of selection varied across years, no net selection on platform length was detected in any of the 3 years. Our results show how the presence of an invasive plant and year-to-year variation in plant-pollinator interactions affect the pollination and components of pollinator-mediated selection in native plants.