UC San Diego

Nestled in the California Floristic Provence, a biodiversity hotspot, San Diego County is home well over 2,500 species of plants and at least 650 bee species, many of which are endemic to the region. Despite the great diversity of pollinators like bees, non-native honey bees (Apis mellifera) make up greater than 70% of all visits to native plants in habitat. Lacking a baseline of pollinators populations and plant reproduction before the arrival of honey bees in the 1800s, the impact of this super abundant non-native species is not well known. In this dissertation, I take an applied and exploratory perspective to study and better understand the effects of honey bees on native plants and pollinators. In the first chapter, I demonstrate that honey bee pollination of native plants leads to decreased fitness of both the parent and progeny generations of three common native plants. In the second chapter, I determine if geitonogamous visitation by honey bees is a conserved behavior throughout its global range by reviewing peer reviewed manuscripts containing relevant information. In the third chapter I quantified the mass of pollen removed by honey bees daily from multiple study sites and estimated the number of native bees of average size that could have been produced with this pollen, and the mass of native bees that could be produced by directly converting observed honey bee biomass into native bees. Finally, in the fourth chapter I set out to determine if honey bees negatively impact native pollinator populations by comparing native pollinator diversity and abundance both in the presence and absence of honey bees using Santa Cruz Island where honey bees have been eradicated, and the Santa Monica Mountains where honey bees persist. Altogether, this work reveals the stunning impact honey bees have on both native plants and pollinators in San Diego County and Southern California. I hope that this dissertation can be used to inform conservationists and policy makers about the impacts of honey bees on our native plants and pollinators so that they may be preserved for generations to come.