UC San Diego

Pollinators are in decline as a result of human activities such as habitat fragmentation. This study examined the effects of habitat fragmentation and reduced bee diversity on the reproductive performance of California poppy, Eschscholzia californica, and clustered tarweed, Deinandra fasciculata, in the San Diego region. We experimentally introduced potted poppy plants in to scrub fragment habitats and natural reserves. We surveyed the potted poppy plants for floral visitors followed by in situ tarweed plants in our field sites after the poppies senesced. Both poppy and tarweed

revealed no difference in reproductive performance between fragments and reserves. Pollinator surveys of poppy and tarweed in fragment and reserve sites also revealed no difference in overall visitor abundance or species richness. However, we found that of the tarweed visitors, reserve sites harbored higher bee species richness than fragment sites. Native pollinator assemblage composition of tarweed visitors also differed between fragment and reserve sites. Honey bees accounted for 61% of all floral visitors observed in all sites. Although we cannot conclude that pollinator diversity played a significant role in the reproduction of poppy and tarweed, results from this study suggest that visitation in fragmented habitats is still sufficient for some native plant species to reproduce successfully. Also, generalist pollinators like honey bees may potentially help buffer against the negative effects of habitat fragmentation on pollinator diversity by maintaining an adequate level of pollination services in the system.