Viable and non-viable seeds in yellow starthistle seed heads are easily distinguishable based on color and shape. Because yellow starthistle requires pollination to produce viable seeds , non-viable seeds represent pollen limitation occurring during the 4-hour period that the flowers were exposed to pollinators. All seeds were counted to compare ratios of viable to non-viable seeds. Any seed predation was noted, and when possible, the seed predator was identified.All analyses were done in R 2.15.1 . Because each site had an AM, Mid-Day, and PM observation event, there were a total of 36 observation events, each with unique wind and temperature recordings, and visit observations of the 15 bee morphotypes. From these, we calculated the total number of bee visitors, total number of bee morphotypes, Shannon diversity of morphotypes, and morphotype evenness. Shannon diversity and evenness were calculated using the R package vegan. The spatial autocorrelation of all bee visitor response variables was assessed by Mantel tests in R package ade4,plastic pots large using the average values for each time of day at each site. Spatial autocorrelation was not detected .
To test for the effect of land use type on each of the response variables we used a generalized linear mixed model using the R package lme4. We designated land use type, bloom category of flowering patch, observation time period, wind, and temperature as fixed effects and site as a random effect. Natural land use and AM observation time period were the model baselines for the categorical variables of land use type and observation time. 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 alinear 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, 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 pantrapping 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 other. 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. The medium hairy leg bee morphotype was not significantly associated with any of the land use typesIt 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,black plastic nursery pots and there may be multiple species that fit within the same morphotype that provide varying degrees of pollination service. 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, 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 its invasion 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.Diet and lifestyle patterns play a significant role in the development of Metabolic Syndrome and the diseases it precipitates, namely cardiovascular disease and type 2 diabetes mellitus. In particular, MetS development is associated with the consumption of foods typical of the Western diet, including red meat and fried foods. The Western diet is characterized by excess intake of energy, readily available carbohydrates and fats that result in postprandial hyperglycemia and hyperlipidemia. Three large scale prospective cohort studies support the relationship of postprandial lipemia and risk of cardiovascular disease. Postprandial inflammation and oxidative stress are postulated to be products of hyperglycemia and lipemia and are associated with impaired insulin sensitivity. Impaired insulin responses to Western meals exaggerate postprandial hyperglycemia and lipemia, creating a vicious cycle leading to vascular dysfunction and damage that, over time, likely augments risk for CVD. Reducing transient fluctuations of these postprandial responses is one lifestyle modification for the prevention and management of MetS. The addition of certain foods to the diet may attenuate these postprandial responses. Foods rich in dietary fiber have been shown to modulate postprandial lipemia and aid in glycemic control.Antioxidant-rich foods have been shown to attenuate postprandial oxidative status markers and increase plasma antioxidant capacity. Few studies have investigated the postprandial response to beans and only one has studied black beans. These few studies have demonstrated that different types of beans elicit different biological responses. This may be in part due to dosing differences, polyphenol bio-availability, and endogenous factors. For example, polyphenols modulate digestive enzymes, eliciting beneficial effects on the postprandial responses. Anthocyanidins in particular, which are found in black beans, have been shown to inhibit α–amylase, maltase, and sucrase activity, which lower postprandial blood glucose. Further, metabolic health benefits of beans are likely related to the functional effects of their inherent dietary fiber and polyphenol content, the latter being questioned as an effect of the general antioxidant properties of polyphenols or a specific effect of the polyphenol structure. Nowadays, it is popular to isolate and sell functional components of foods as dietary supplements and many supplements are marketed for their “antioxidant” properties.