Shannon diversity and evenness were fit with Gaussian distributions while all other variables were fit with Poisson distributions. In comparing the ratios of viable seeds to total seeds vs. the ratio of viable seeds to counted stigmas, we found that there was a strong correlation between these metrics. To look at the effect of land use type on seed-set, we therefore decided to utilize the ratio of viable seeds to total seeds in each seed head that did not experience seed predation, because of error in counting the number of stigmas . We then used a generalized linear mixed model fit with a Binomial distribution, with land use type as a fixed effect and site as a random effect. Finally, we tested for an effect of floral visitor observations on yellow starthistle seed set at each site. We averaged the number of visits from each morphotype across temporal observation events at the same site. Morphotypes that averaged at least one visit per 30 minute observation window were included as fixed effects in a linear mixed model fit with a binomial distribution, with site as a random effect and the ratio of viable to total seeds as the response variable. We also modeled the effects of total bee visitation, morphotype richness, and morphotype diversity on seed set ratios.Our results show that rates of bee visitation and seed set vary among urban, agricultural, square plastic plant pot and natural landscapes, demonstrating the importance of land use in the dynamics of plant pollinator interactions.
We suggest that these effects are at least in part explained by floral availability, a vital bee resource, which can be highly variable among different land use types. For example, in August there are few plants in flower besides yellow starthistle in the natural areas of Contra Costa County, California, whereas in urban and agricultural areas there are many exotic plants and supplementary inputs available . From pan-trapping of bee specimens in the region , we know that total bee abundance is highest in the spring in natural areas. However, towards the end of the summer when yellow starthistle is in flower, there is little difference in collected bee abundance between human altered landscapes and natural areas, and human-altered areas may even exhibit overall higher bee abundance. Our results of bee visitation to yellow starthistle support this pattern. Agricultural areas have large populations of managed honey bee colonies, so one would predict visitation to yellow starthistle by honey bees to be positively associated with surrounding agricultural land use. By contrast for native bees , the highest rates of visitation to yellow starthistle were in sites with more surrounding urban land use. Urban gardens have many exotic plants, often selected for aesthetic purposes, many of which are in flower later in the season than most California native plants. In addition, many of the plants in urban areas both directly and indirectly receive supplementary resources, particularly water, that further extend their flowering time.
Even though agricultural areas also have supplementary resources, the main crop in flower in East Contra Costa County later in the season is maize, which is wind pollinated. There may be multiple impacts of exotic plants in urban areas. By filling the phenological flowering gap noted above, they may help attract even larger populations of bees into the urban landscape. In addition, bees in urban sites may be behaviorally more likely to visit non-native plants due to the increased encounters they have with novel plants.In agricultural and natural landscapes, a positive correlation between pollinator visitation and seed set is typical. Surprisingly in our system, in human-altered landscapes, higher total observed bee visitation did not result in higher proportions of seed set, as would be expected. In fact, urban areas, despite receiving the highest rates of native bee visitation, exhibited the lowest rates of seed set. Conversely, natural areas, which received the lowest amount of total bee visitation, had the highest rates of seed set. We suggest 2 possible explanations for this discrepancy between pollinator visitation and rates of seed set: 1) pollinator efficiency; and/or 2) the composition of the local flowering community. Depending on the plant, certain pollinator species are much more effective than others. For example, Osmia, Habropoda, and Apis, have been found to produce varying amounts of seed set as a result of a single visit to blueberry, but these results vary slightly depending on the blueberry variety. In the case of yellow starthistle, it is likely that the most frequent visitors are perhaps not the most efficient. When we directly compared average seed set at each site against visitation rates, we found a significant positive association with the medium hairy leg bees.
The medium hairy leg bee morphotype includes those species which fall in both the Tribes Emphorini and Eucerini. Emphorini are known to largely be oligolectic , meaning they specialize on certain plant groups, which theory suggests would make them more efficient pollinators than generalists. It was also the only group that was observed most frequently during morning sampling, perhaps reflecting a difference in when yellow starthistle is most receptive to pollination. Despite the overwhelming abundance of honey bees in agriculture areas, we did not observe higher seed set in those regions, consistent with the observation that honey bees can be poorer pollinators than other species. It is also important to note that this study used a morphotype classification, and there may be multiple species that fit within the same morphotype that provide varying degrees of pollination services. It is possible there are rare, but highly efficient, pollinators that were rarely observed during the sampling period, or were lumped together with a more frequently observed morphotype. An alternative explanation for the lack of an association between floral visitation and seed set is that higher plant diversity in urban and agricultural areas may decrease pollinator efficiency. Previous research has shown that invasive alien plants can have a negative effect on native plant communities by acting as attractors for pollinators, or decreasing pollinator efficiency by providing a wider range of resources for pollinators to visit, with the consequence that visitors transfer pollen from non con-specifics, potentially clogging stigmas and reducing pollination success. In this case, our target plant, yellow starthistle is indeed considered an invasive alien plant, but the hypothesis of it being in a novel diverse community could lead to a similar effect on the frequency and quality of pollination services that it receives. In sites where there are many other potential plants to visit and accompanying decreased floral fidelity leading to diverse pollen loads, one predicts decreased pollinator efficiency. Abundant sources of exotic plant pollen could occur in areas where there is a greater diversity of nearby plants for pollinators to visit. This explanation might account for the observation that shield tipped small dark bees were negatively correlated with seed set. We selected yellow starthistle as the target plant for this study because of its ubiquitous distribution, reliance on pollination, 25 liter square pot and its attraction for a wide set of visitors; it is also a highly invasive and undesirable plant. Previous research on yellow starthistle has found that itsinvasion can be facilitated other non-native pollinator species such as the honey bee, Apis mellifera, and the starthistle bee, Megachile apicalis, which is included in the medium striped hairy belly bee morphotype. However, the abundance of bees in both of these 2 morphotypes were most closely associated with agricultural areas, which did not have the highest rates of seed set as would be predicted by visitation alone. Our results indicate clearly that bee visitation in human-altered landscapes can be higher than that in comparable natural areas, especially towards the end of the flowering season when there are few resources available in natural landscapes. Because the response of bee visitors to land use change depends on species-specific requirements and these pollinators also have variable effects on plants, understanding the effect of land use change on pollination services requires knowledge not only of which pollinator groups shift to the human-altered landscapes, but also the rate of pollination that those groups have on the plant species in those landscapes. Future research will benefit from looking at a wider range of plants with a different range of target pollinators and that flower earlier in the year to better tease out these hypotheses.
If the patterns of bee visitation and seed set that we observed are indeed consistent across other plant species, the novel plant communities created in these human-altered landscapes and the generalist bee species that are favored in such landscapes will lead to a reduction in overall pollination services. As a viscous soluble fiber, pectin is associated with lowering blood serum total cholesterol and low-density lipoprotein cholesterol , without changing high-density lipoprotein cholesterol . By increasing satiety, pectin can help weight control by reducing food consumption. . Due to its complex structure, pectin is a common drug formulation agent for oral delivery, in the form of tablets, gels, hydrogels, beads, aerogels, coated, and compression-coated dosage . It is especially beneficial for colonspecific drugs as the bio-active compounds, mostly short-chain fatty acids, and can be released after hydrolyzation of pectinolytic enzymes and microorganisms in the colon . The rhamnogalacturonan type I fragments within the pectin also have lower molecular weight to function as an anticancer down-regulator of galectin-3, which is a pro-metastatic protein in many cancer cells. Pectin has also been used to nano-encapsulate bio-active compounds, thereby enhancing shelf life and stability.Pectin is considered a safe food substance through various government food agencies. Even though its usage and composition are regulated under different food additive laws, the Food and Drug Administration of the U.S. considers it GRAS. At the Joint FAO/WHO Expert Committee Report on Food Additives and in the European Union, no numerical acceptable daily intake has been set, as pectin is considered safe. Its abundant benefits stimulated great demands and the global pectin market size was valued at USD 964.1 million in 2015 .Polyphenol compounds can bind with the cell wall polysaccharides to strengthen the structure . In return, CPSs can interact with polyphenols to modify their bio-accessibility, bio-availability, and bio-efficacy . Liu et al., summarized multiple research that has been done to investigate the binding effects between pectin and polyphenol. Noncovalent bonds are dominant in the polyphenol-pectin interactions, such as hydrogen bonds, hydrophobic interactions, electrostatic interactions. These weak bonds are sensitive to the intrinsic properties of polyphenol and pectin , as well as environmental conditions .Considering the binding property of pectin and polyphenols, a co-extraction of pectin and polyphenol should be considered because of the following advantages: Boosted stability of polyphenol and overall antioxidant activity; and Enhanced unique and beneficial characteristics for developing novel food products. As for stability, Oszmiański et al. proposed a cooperative hydrogen bond or hydrophobic interactions existed between the oxygen atom of pectin and the phenolic hydroxyl group. A natural pectin coating is speculated as less loss of polyphenols was observed due to the limited oxygen contact. The strength of pectin-polyphenol interaction is mainly determined by the non-covalent bonds, including hydrogen bonds, ionic bonds, and hydrophobic forces. Regarding the quality improvement, Hayashi et al., found the astringency of gallate-type polyphenol was reduced by the addition of pectin. A similar finding was reported in persimmons .Pectin polymer degradation is a fundamental step of extraction. The common degradation approaches include chemical hydrolysis, heating, radiation, and enzymatic reaction. Acid hydrolysis on pectin was one of the most conventional chemical degradation methods. Thibault et al. studied the mild acid hydrolysis of apple, beet, and citrus pectin. Inorganic solvents, including HCl and HNO3, have been widely used in the industry. However, they raised concerns in food applications and were difficult to recover, thus causing undesired pollution and high processing cost . Novel technologies with reduced pollution are in demand.Physical technologies, such as the non-thermal process, were superior due to their high efficiency, reduced pollution and cost, and ease of control. Ultrasound as a novel non-thermal technology has been widely applied in food industries, including extraction, preservation, emulsification, filtration, and cutting . Successful ultrasound applications in pectin extraction include citrus , apple , and sweet potato . Ultrasound extraction combined with acid hydrolysis was reported to further increase the pectin yield. Muñoz-Almagro et al. studied the pectin degradation under ultrasound power of 400 W in the presence of nitric acid and citric acid .