These results suggest that the existing literature identifies few actual foraging associations for the vast majority of bee genera in California, This dearth of information shows the importance of this study and the need for further research in this area. The model independence tests for each respective bee genus observed in the Arboretum reveals that 15 of the 28 models are highly significant at levels below 0.01 with degrees of freedom ranging from 1-237. The remaining models were found to be lacking independence mostly due to a low frequency of use from our observations for those bee genera.According to these results, it is possible to build foraging models for bees based on floral foraging preferences. However, while the aggregate model evaluation scored quite well overall with Table 1 plants being utilized for forage by bees, analysis of the bee-to-plant associations demonstrated that the individual models were not as predictive at the finer scale of bees to specific plant genera, mostly due to the high omission rates. Thus, bees were found to be using many more plants than the predictive plants alone in Table 1. Future research should focus on better understanding bee-to-plant associations. Furthermore, plastic flower buckets wholesale investigating the spatial consequences of bee-to-plant associations is essential in studying habitat connectivity and fragmentation for bee genera.
Studying bees at the genus level was effective for observation of their foraging preferences and trends, which require specific conservation strategies. The variability of results between bee genera emphasizes that, for more effective conservation, beegenera should be studied individually from each other, using an autecological approach, and not aggregated to achieve more effective conservation. Overall, there was much variability in the degree to which bee genera utilized Table 1 plants or not . In contrast to Frankie’s estimate of 17 common bee genera in California , we found 27 bee genera observed to be foraging in the Arboretum, five of which were not predicted to have been there . The 22 predicted bee genera included: Agapostemon, Andrena, Anthidium, Anthophora, Apis, Ashmeadiella, Bombus, Ceratina, Coelioxys, Diadasia, Eucera, Habropoda, Halictus, Hoplitus, Hylaeus, Lasioglossum, Megachile, Melissodes, Osmia, Peponapis, Svastra, and Xylocopa. At 27 observed bee genera, our findings demonstrated only one more bee genus than Robbin Thorp’s confirmed personal collection of 26 bee genera found in Davis, California. It is a good sign that our findings closely confirm the local expert’s specimen collection. Map accuracy was very helpful in determining the presence or absence of bees. Interestingly, as a whole, bees utilized 84 of the 134 plants they were predicted to use in the Arboretum per Table 1. Since bees utilized 297 forage plants, 213 plants were novel plants not included in Table 1.
Error analysis demonstrated variability in predictive success between bee genera. The genera Anthophora, Diadasia, and Habropoda demonstrated the highest true positive fractions; theywere the most predictable in terms of their feeding preferences, ranging from 0.3-0.5. On average, for all bees, the sensitivity score was low, at 0.14, meaning only 14% of the literature’s plants were predicted ‘correctly’ with the corresponding bee association. Conversely, the false negative fraction of 0.86 means that 86% of bee foraging was not predicted via the existing literature models. Therefore, it is valuable to compare separately multiple bee genera and also their foraging preference associations within the same study. Studies which aggregate all bees risk erroneous conclusions regarding the relationships between bee and plant genera. Similarly, studies of only one bee genera are unlikely to be comprehensive enough to encompass conservation of a diversity of bees. We have demonstrated that different angles of model analysis can yield varied ranges of success. Our findings indicate the existing plant lists currently lack effectiveness to comprehensively predict bee genera foraging in California. These results emphasize how more needs to be learned about bee genera foraging patterns. We suggest more research should be done to collect and publish bee association data. Moreover, these findings also show how strongly plant selection can influence garden habitats for bee genera. Table 3 shows how the Arboretum gardens vary greatly in their ability to attract bees and also sustain them over time.
Gardens which facilitate the most foraging over time represent models for how urban planting schemes could attempt to accommodate and conserve California’s bees. The Mary Wattis Brown California native garden and Ruth Storer Arboretum All-Star garden perform the best at providing bee habitat. Therefore, future garden design to support bees should be based off of the planting characteristics of both garden types,maximizing plants best at supporting bee foraging. Furthermore, almost all bees were found to forage on exotic plant species which were not emphasized on some of the recommended suitable plant lists . The observed opportunistic foraging nature of bees shows that reconciliation ecology seems in part suitable for maximizing bee habitat conservation and design. This study presents compelling evidence that that current suggested plant lists have significant inadequacies as habitat for bees. Furthermore, this research has identified many plants within the Arboretum’s novel plant communities that are highly functional as habitat for California’s native bees . To further improve bee habitat relationship model information, habitat elements required to support bee nesting need to be included. In future research, it would be valuable to add further layers of information, such as nesting resources, to increase the helpfulness of the model toward building or predicting comprehensive suitable habitat, not just foraging. For example, the primary means of reproduction by most native bees is usually one of three strategies : ground nesting types, cavity nesting in trees or plant stems, and plant stems, both woody and herbaceous. There may be also be garden physical form factors regarding pollinator attractiveness and this should be addressed in future research. For example, the age of the plants, degree of under or overstory, sun aspect ratio, and more. Detailed bee landscape design is explored in Chapter 2 in depth.Since the existing bee-plant lists seemed to be under performing, we conducted further investigations into these list inadequacies. The existing literature plant list included 61%native California plants and 38% non-native, while our foraging study showed nearly an inverse in the actual feeding trends, with 43% native California plants and 57% non-native. In addition, among plants which were not listed in Table 1, “unexpected novel” foraging plants, only 36% were California natives, while 64% were non-natives. Scientists may have overvalued the forage attractiveness of native plants for bees and undervalued the positive function of nonnative plants. For example, an urban ecology study in the Central Valley of California by Shapiro found 40% of lepidopteran faunal host plants are non-native plants. While California native plants contribute many evolutionary and ecological aspects to a site, black flower buckets our study showed that bees in horticultural environments exhibit trends of feeding opportunistically and without majority preference for the native status of a plant. As climate change increasingly puts stresses on native plants forcing range contractions and expansions, exotic plant species may ultimately need to be utilized to maintain and conserve native bees.
The UC Davis Arboretum and Public Garden hosts a variety of specialty gardens, boasting plants curated from geographically distant locations. However, the Arboretum plantings have been consciously selected to suit the local Mediterranean climate. The Arboretum tends not to grow plants which require intensive care and high water demands, rather they take low maintenance approach, with policies about not fertilizing and/or spraying for pests, for example, and this is beneficial to bees. Furthermore, the Arboretum has a plant promotion program called the “AllStars” and one hundred Arboretum All-Star plants were selected for climate suitability, some native, some not, with an emphasis on low-water use plants and also attractiveness from the human perspective . Many of these plants were also found to be utilized by bees. This study allowed a unique look at how California native bees perceive unique foraging opportunities, some of which were previously unknown, but seemingly beneficial. Among nonnative plants there are consistent trends of plant origin . Based on observed foraging results, from a bee’s perspective, the Arboretum would improve bee foraging by adding more drought tolerant plants from Africa, Australia, Europe, South Africa, South America, the Canary Islands, and New Zealand.It is essential to better understand bee foraging from a bees’ perspective in order to design suitable habitat. This research has demonstrated the limitations of currently understood bee-toplant associations. The basic connection of a bee to its foraging plants is essential to understand which types of habitats are appropriate or not. WHR accuracy can be improved with extensive empirical testing. This study elucidates the need for further quantitative studies on bee WHR models. Through accommodating native bees in novel ecosystems, such as in gardens and in hedgerows near agricultural crops, valuable pollination services can be conserved for the benefit of people, agriculture, and natural communities.Reconciliation ecology provides one of the best frameworks for resilient bee habitat design. The data from this study have shown there are benefits to using both California native plants as well as non-natives to achieve peak foraging habitat for California native bees, as well as naturalized European honey bees. As seen in the Arboretum’s themed gardens, bees are utilizing the novel plantings which also were selected for drought tolerance and aesthetic beauty. By combining the best foraging plants, landscape designers can significantly improve foraging habitats for native bees. Best management practices and design responses for improving bee habitat are likely to be very specialized to increase foraging optimization at designed garden sites. For example, in California’s Central Valley drought tolerance is a very important plant attribute since water will likely become less available in the future due to climactic water deficit projections . Therefore, a design framework should be responsive to a site’s prioritized ecological needs.Although the data collected for this study is extensive in time and space, it represents just one year of bee-plant visitation in the Arboretum. Thus, interannual variability of weather and climate could produce other visitation patterns. However, we feel we captured much intraannual variability with our sampling approach. This study was conducted in the Central Valley ecoregion of California and this could produce biased results towards the bees associated with this ecoregion. As noted in the Introduction WHR models tend to be regional in nature and therefore results may not transfer to all other areas of California. All methods for bee fieldwork have gone under scrutiny in recent years, which are not unique to this study. It also should be pointed out that this study did not explicitly evaluate nesting habitat at the study site.Development of WHR models for native bees is an important step in conservation planning for these species. They can be significantly improved with additional field studies regarding bee foraging plants. In particular, it is important to study bee-to-plant associations, which are currently not well understood or, in the case of novel associations, underrepresented. More quantitative foraging studies should be undertaken to make accurate foraging models. Results from this study show that more optimal pollinator plantings could be designed and constructed in a more strategic and scientific manner. Using data from this study, plant palettes for ideal garden design for native bee conservation could be created from a bee’s point of view. Many bees in this research project were found to be opportunistic foragers—neither exclusively utilizing native or non-native plants. Thus, bees may have more opportunities to thrive if they are given a broader spectrum of plants, which can be done through strategic conservation actions in both space and time. This study elucidates the feeding preferences of native bees, which can be used to better manage and conserve them in the California landscape. How many other foraging plants would native bees use or prefer? This can only be answered with further empirical studies and assessment of possible plant candidates for native bees.Bees are a diverse suite of insects which provide the greatest percentage of plant pollination in the world . The ecosystem services that bees provide are essential to people and the world’s ecosystems. Bees also pollinate the majority of food plants that humans consume . It is estimated that up to two-thirds of food crops for humans require bee pollination of which native bees have been estimated to contribute, around 50 percent of bee foraging activity .