Native and non-native plants attract diverse bees to urban gardens in California

Abstract

Bees visit native and non-native plant species for pollen and nectar resources in urban, agricultural, and wildland environments. Results of an extensive survey of bee-flower collection records from 10 California cities from 2005-2011 were used to examine host-plant records of native and non-native ornamental plants to diverse native and non-native bee species; five cities were from northern California and five were from southern California. A total of 7,659 bees and their floral host plants were examined. Of these, 179 were Apis mellifera and 7,390 were non-Apis. Only four other non-native species (all in Megachilidae) were recorded in the survey, and together they accounted for 402 individuals. These bees have been databased in preparation for deposition in the University of California-Berkeley Essig Museum of Entomology. We identified 229 bee species and 42 genera visiting native and non-native plant types in urban areas. Of the 229 species, 71 bee species were collected from only native plants; 52 were collected from only non-native host plants; and 106 were collected from both types of plants. Native bee species were common on native plants and non-native plants, but there were substantially more non-native bee species visiting non-native plants compared to native plants. Flowering periods in months were similar for both types of plants, but non-natives tended to flower later in the year. We propose that using native and non-native plants improves habitat gardening by increasing opportunities for attracting a richer diversity of bee species and for longer periods. Knowing basic bee-flower relationships in an area is key to planning a bee habitat garden with a variety of plant types, regardless of their geographic origin.

Decline in wild bee species richness associated with honey bee (Apis melliferaL.) abundance in an urban ecosystem

“…Our results did not detect an effect of honey bee abundance on overall native bee species richness ( Table S3 ), but the 13 species that were absent from sites that had the highest increases in honey bee abundance since 2013, were native species ( Table S4 ). As urban floral communities are often dominated by exotic and cultivated plants, and native bees tend to prefer native plants, exotic bees are thought to have an advantage in urban environments ( Banaszak-Cibicka & Zmihorski, 2012 ; Frankie et al, 2019 ). However, generalist bees that tolerate a broad range of flowering plant species may have greater competitive ability than specialist species, regardless of native status.…”

Non-Native Non-Apis Bees Are More Abundant on Non-Native Versus Native Flowering Woody Landscape Plants

“…Similar patterns have been documented for non-native bees foraging on herbaceous plants; e.g., European bumble bees introduced into New Zealand showed strong foraging preference for European-origin plants [ 44 ]. Similarly, native bee species were common on both native and non-native herbaceous plants in California urban gardens, but substantially more non-native bee species visited non-native plants than native ones [ 10 ]. All of the non-native woody plants we sampled are also visited by native bees [ 9 ].…”

“…Although flowering woody landscape plants provide many ecosystem services and are selected for a variety of reasons besides pollinator conservation [ 56 ], their value for supporting urban bees is increasingly recognized [ 8 , 9 , 57 ]. Many species and cultivars of non-native herbaceous and woody ornamental plants provide floral resources to both native and non–native bees [ 6 , 7 , 8 , 9 , 10 , 11 , 14 , 15 , 57 , 58 , 59 ]. Plants introduced into new regions tend to retain the phenology of their natal provenance, so incorporating some non-natives into urban landscapes can benefit bees by extending the flowering season.…”

“…For example, urban landscapes dominated by non–native plants (i.e., those that evolved outside of local food webs) may be inhospitable to native caterpillars and thus to birds that rear their young on insect prey [ 5 ]. In contrast, many species of cultivated non-native plants provide floral resources to urban bees [ 6 , 7 , 8 , 9 , 10 , 11 ].…”

“…Seasonal timing of bloom tends to be conserved by biogeographic origin, with plants introduced into new regions retaining the phenology of their natal provenance [ 12 , 13 ]. Thus, some authors, e.g., [ 9 , 10 , 14 , 15 ], suggest that, in anthropogenically-transformed managed urban gardens and landscapes, incorporating some non-invasive non-native plant species can help to support pollinators by ensuring succession of overlapping bloom periods, supporting seasonal specialists, and providing floral resources before and after peak bloom of native plants. Most urban bee species are polylectic and readily incorporate pollen and nectar from novel plants into their diets [ 13 , 16 , 17 ].…”