@phdthesis{Seitz2020,
  author    = {Seitz, Nicola},
  title     = {Bee demise and bee rise: From honey bee colony losses to finding measures for advancing entire bee communities},
  doi       = {10.25972/OPUS-18418},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-184180},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2020},
  abstract  = {My dissertation comprises three studies: (1) an assessment of honey bee colony losses in the USA between 2014 and 2015, (2) an exploration of the potential of reclaimed sand mines as bee habitat, and (3) an evaluation of native and non-native pollinator friendly plants in regard to their attraction to bees. While the first study focuses on honey bees, the latter two studies primarily take wild bees or entire bee communities in focus. The study on honey bee colony losses was conducted within the framework of the Bee Informed Partnership (BIP, beeinformed.org) and aligns with the annual colony loss surveys which have been conducted in the USA since the winter of 2006/2007. It was the fourth year for which summer and annual losses were calculated in addition to winter losses. Among participants, backyard beekeepers were the largest group (n = 5690), although sideline (n = 169) and commercial (n = 78) beekeepers managed the majority (91.7 \%) of the 414 267 surveyed colonies. Overall, 15.1 \% of the estimated 2.74 million managed colonies in the USA were included in the study. Total honey bee colony losses (based on the entirety of included colonies) were higher in summer (25.3 \%) than in winter (22.3 \%) and amounted to 40.6 \% for the entire 2014/2015 beekeeping year. Average colony losses per beekeeper or operation were higher in winter (43.7 \%) than in summer (14.7 \%) and amounted to 49 \% for the entire 2014/2015 beekeeping year. Due to the dominance of backyard beekeepers among participants, average losses per operation (or unweighted loss) stronger reflected this smaller type of beekeeper. Backyard beekeepers mainly named colony management issues (e.g., starvation, weak colony in the fall) as causes for mortality, while sideline and commercial beekeepers stronger emphasized parasites or factors outside their control (e.g., varroa, nosema, queen failure). The second study took place at reclaimed sand mines. Sand mines represent anthropogenically impacted habitats found worldwide, which bear potential for bee conservation. Although floral resources can be limited at these habitats, vegetation free patches of open sandy soils and embankments may offer good nesting possibilities for sand restricted and other bees. We compared bee communities as found in three reclaimed sand mines and at adjacent roadside meadows in Maryland, USA, over two years. Both sand mines and roadsides hosted diverse bee communities with 111 and 88 bee species, respectively. Bee abundances as well as richness and Shannon diversity of bee species were higher in sand mines than at roadsides and negatively correlated with the percentage of vegetational ground cover. Species composition also differed significantly between habitats. Sand mines hosted a higher proportion of ground nesters, more uncommon and more 'sand loving' bees similar to natural sandy areas of Maryland. Despite the destruction of the original pre-mining habitat, sand mines thus appear to represent a unique habitat for wild bees, particularly when natural vegetation and open sand spots are encouraged. Considering habitat loss, the lack of natural disturbance regimes, and ongoing declines of wild bees, sand mines could add promising opportunities for bee conservation which has hitherto mainly focused on agricultural and urban habitats. The third study was an experimental field study on pollinator friendly plants. Bees rely on the pollen and nectar of plants as their food source. Therefore, pollinator friendly plantings are often used for habitat enhancements in bee conservation. Non-native pollinator friendly plants may aid in bee conservation efforts, but have not been tested and compared with native pollinator friendly plants in a common garden experiment. In this study, we seeded mixes of 20 native and 20 non-native pollinator friendly plants in two separate plots at three sites in Maryland, USA. For two years, we recorded flower visitors to the plants throughout the blooming period and additionally sampled bees with pan traps. A total of 3744 bees (120 species) were sampled in the study. Of these, 1708 bees (72 species) were hand netted directly from flowers for comparisons between native and non-native plants. Depending on the season, bee abundance and species richness was either similar or lower (early season and for richness also late season) at native plots compared to non-native plots. Additionally, the overall bee community composition differed significantly between native and non-native plots. Furthermore, native plants were associated with more specialized plant-bee visitation networks compared to non-native plants. In general, visitation networks were more specialized in the early season than the later seasons. Four species (Bombus impatiens, Halictus poeyi/ligatus, Lasioglossum pilosum, and Xylocopa virginica) out of the five most abundant bee species (also including Apis mellifera) foraged more specialized on native than non-native plants. Our study showed that non-native plants were well accepted by a diverse bee community and had a similar to higher attraction for bees compared to native plants. However, we also demonstrated alterations in foraging behavior, bee community assemblage, and visitation networks. As long as used with caution, non-native plants can be a useful addition to native pollinator friendly plantings. This study gives a first example of a direct comparison between native and non-native pollinator friendly plants.},
  subject      = {Biene},
  language  = {en}
}
@article{SeitzvanEngelsdorpLeonhardt2020,
  author    = {Seitz, Nicola and vanEngelsdorp, Dennis and Leonhardt, Sara D.},
  title     = {Are native and non-native pollinator friendly plants equally valuable for native wild bee communities?},
  series = {Ecology and Evolution},
  volume    = {10},
  journal   = {Ecology and Evolution},
  number    = {23},
  doi       = {10.1002/ece3.6826},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-218439},
  pages     = {12838-12850},
  year      = {2020},
  abstract  = {Bees rely on floral pollen and nectar for food. Therefore, pollinator friendly plantings are often used to enrich habitats in bee conservation efforts. As part of these plantings, non-native plants may provide valuable floral resources, but their effects on native bee communities have not been assessed in direct comparison with native pollinator friendly plantings. In this study, we performed a common garden experiment by seeding mixes of 20 native and 20 non-native pollinator friendly plant species at separate neighboring plots at three sites in Maryland, USA, and recorded flower visitors for 2 years. A total of 3,744 bees (120 species) were collected. Bee abundance and species richness were either similar across plant types (midseason and for abundance also late season) or lower at native than at non-native plots (early season and for richness also late season). The overall bee community composition differed significantly between native and non-native plots, with 11 and 23 bee species being found exclusively at one plot type or the other, respectively. Additionally, some species were more abundant at native plant plots, while others were more abundant at non-natives. Native plants hosted more specialized plant-bee visitation networks than non-native plants. Three species out of the five most abundant bee species were more specialized when foraging on native plants than on non-native plants. Overall, visitation networks were more specialized in the early season than in late seasons. Our findings suggest that non-native plants can benefit native pollinators, but may alter foraging patterns, bee community assemblage, and bee-plant network structures.},
  language  = {en}
}
@article{Voulgari‐KokotaAnkenbrandGrimmeretal.2019,
  author    = {Voulgari-Kokota, Anna and Ankenbrand, Markus J. and Grimmer, Gudrun and Steffan-Dewenter, Ingolf and Keller, Alexander},
  title     = {Linking pollen foraging of megachilid bees to their nest bacterial microbiota},
  series = {Ecology and Evolution},
  volume    = {2019},
  journal   = {Ecology and Evolution},
  number    = {9},
  issn      = {00},
  doi       = {10.1002/ece3.5599},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-201749},
  pages     = {10788-10800},
  year      = {2019},
  abstract  = {Solitary bees build their nests by modifying the interior of natural cavities, and they provision them with food by importing collected pollen. As a result, the microbiota of the solitary bee nests may be highly dependent on introduced materials. In order to investigate how the collected pollen is associated with the nest microbiota, we used metabarcoding of the ITS2 rDNA and the 16S rDNA to simultaneously characterize the pollen composition and the bacterial communities of 100 solitary bee nest chambers belonging to seven megachilid species. We found a weak correlation between bacterial and pollen alpha diversity and significant associations between the composition of pollen and that of the nest microbiota, contributing to the understanding of the link between foraging and bacteria acquisition for solitary bees. Since solitary bees cannot establish bacterial transmission routes through eusociality, this link could be essential for obtaining bacterial symbionts for this group of valuable pollinators.},
  language  = {en}
}
@phdthesis{SchenkneeWolf2018,
  author    = {Schenk [n{\´e}e Wolf], Mariela},
  title     = {Timing of wild bee emergence: mechanisms and fitness consequences},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-161565},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {Solitary bees in seasonal environments have to align their life-cycles with favorable environmental conditions and resources. Therefore, a proper timing of their seasonal activity is highly fitness relevant. Most species in temperate environments use temperature as a trigger for the timing of their seasonal activity. Hence, global warming can disrupt mutualistic interactions between solitary bees and plants if increasing temperatures differently change the timing of interaction partners. The objective of this dissertation was to investigate the mechanisms of timing in spring-emerging solitary bees as well as the resulting fitness consequences if temporal mismatches with their host plants should occur. In my experiments, I focused on spring-emerging solitary bees of the genus Osmia and thereby mainly on O. cornuta and O. bicornis (in one study which is presented in Chapter IV, I additionally investigated a third species: O. brevicornis). Chapter II presents a study in which I investigated different triggers solitary bees are using to time their emergence in spring. In a climate chamber experiment I investigated the relationship between overwintering temperature, body size, body weight and emergence date. In addition, I developed a simple mechanistic model that allowed me to unite my different observations in a consistent framework. In combination with the empirical data, the model strongly suggests that solitary bees follow a strategic approach and emerge at a date that is most profitable for their individual fitness expectations. I have shown that this date is on the one hand temperature dependent as warmer overwintering temperatures increase the weight loss of bees during hibernation, which then advances their optimal emergence date to an earlier time point (due to an earlier benefit from the emergence event). On the other hand I have also shown that the optimal emergence date depends on the individual body size (or body weight) as bees adjust their emergence date accordingly. My data show that it is not enough to solely investigate temperature effects on the timing of bee emergence, but that we should also consider individual body conditions of solitary bees to understand the timing of bee emergence. In Chapter III, I present a study in which I investigated how exactly temperature determines the emergence date of solitary bees. Therefore, I tested several variants degree-day models to relate temperature time series to emergence data. The basic functioning of such degree-day models is that bees are said to finally emerge when a critical amount of degree-days is accumulated. I showed that bees accumulate degree-days only above a critical temperature value (~4°C in O. cornuta and ~7°C in O. bicornis) and only after the exceedance of a critical calendar date (~10th of March in O. cornuta and ~28th of March in O. bicornis). Such a critical calendar date, before which degree-days are not accumulated irrespective of the actual temperature, is in general less commonly used and, so far, it has only been included twice in a phenology model predicting bee emergence. Furthermore, I used this model to retrospectively predict the emergence dates of bees by applying the model to long-term temperature data which have been recorded by the regional climate station in W{\"u}rzburg. By doing so, the model estimated that over the last 63 years, bees emerged approximately 4 days earlier. In Chapter IV, I present a study in which I investigated how temporal mismatches in bee-plant interactions affect the fitness of solitary bees. Therefore, I performed an experiment with large flight cages serving as mesocosms. Inside these mesocosms, I manipulated the supply of blossoms to synchronize or desynchronize bee-plant interactions. In sum, I showed that even short temporal mismatches of three and six days in bee-plant interactions (with solitary bee emergence before flower occurrence) can cause severe fitness losses in solitary bees. Nonetheless, I detected different strategies by solitary bees to counteract impacts on their fitness after temporal mismatches. However, since these strategies may result in secondary fitness costs by a changed sex ratio or increased parasitism, I concluded that compensation strategies do not fully mitigate fitness losses of bees after short temporal mismatches with their food plants. In the event of further climate warming, fitness losses after temporal mismatches may not only exacerbate bee declines but may also reduce pollination services for later-flowering species and affect populations of animal-pollinated plants. In conclusion, I showed that spring-emerging solitary bees are susceptible to climate change as in response to warmer temperatures bees advance their phenology and show a decreased fitness state. As spring-emerging solitary bees not only consider overwintering temperature but also their individual body condition for adjusting emergence dates, this may explain differing responses to climate warming within and among bee populations which may also have consequences for bee-plant interactions and the persistence of bee populations under further climate warming. If in response to climate warming plants do not shift their phenologies according to the bees, bees may experience temporal mismatches with their host plants. As bees failed to show a single compensation strategy that was entirely successful in mitigating fitness consequences after temporal mismatches with their food plants, the resulting fitness consequences for spring-emerging solitary bees would be severe. Furthermore, I showed that spring-emerging solitary bees use a critical calendar date before which they generally do not commence the summation of degree-days irrespective of the actual temperature. I therefore suggest that further studies should also include the parameter of a critical calendar date into degree-day model predictions to increase the accuracy of model predictions for emergence dates in solitary bees. Although our retrospective prediction about the advance in bee emergence corresponds to the results of several studies on phenological trends of different plant species, we suggest that more research has to be done to assess the impacts of climate warming on the synchronization in bee-plant interactions more accurately.},
  subject      = {wild bees},
  language  = {en}
}
@article{BartomeusPottsSteffanDewenteretal.2014,
  author    = {Bartomeus, Ignasi and Potts, Simon G. and Steffan-Dewenter, Ingolf and Vaissiere, Bernard E. and Woyciechowski, Michal and Krewenka, Kristin M. and Tscheulin, Thomas and Roberts, Stuart P. M. and Szentgyoergyi, Hajnalka and Westphal, Catrin and Bommarco, Riccardo},
  title     = {Contribution of insect pollinators to crop yield and quality varies with agricultural intensification},
  series = {PEERJ},
  volume    = {2},
  journal   = {PEERJ},
  number    = {e328},
  issn      = {2167-9843},
  doi       = {10.7717/peerj.328},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-116928},
  year      = {2014},
  abstract  = {Background. Up to 75\% of crop species benefit at least to some degree from animal pollination for fruit or seed set and yield. However, basic information on the level of pollinator dependence and pollinator contribution to yield is lacking for many crops. Even less is known about how insect pollination affects crop quality. Given that habitat loss and agricultural intensification are known to decrease pollinator richness and abundance, there is a need to assess the consequences for different components of crop production. Methods. We used pollination exclusion on flowers or inflorescences on a whole plant basis to assess the contribution of insect pollination to crop yield and quality in four flowering crops (spring oilseed rape, field bean, strawberry, and buckwheat) located in four regions of Europe. For each crop, we recorded abundance and species richness of flower visiting insects in ten fields located along a gradient from simple to heterogeneous landscapes. Results. Insect pollination enhanced average crop yield between 18 and 71\% depending on the crop. Yield quality was also enhanced in most crops. For instance, oilseed rape had higher oil and lower chlorophyll contents when adequately pollinated, the proportion of empty seeds decreased in buckwheat, and strawberries' commercial grade improved; however, we did not find higher nitrogen content in open pollinated field beans. Complex landscapes had a higher overall species richness of wild pollinators across crops, but visitation rates were only higher in complex landscapes for some crops. On the contrary, the overall yield was consistently enhanced by higher visitation rates, but not by higher pollinator richness. Discussion. For the four crops in this study, there is clear benefit delivered by pollinators on yield quantity and/or quality, but it is not maximized under current agricultural intensification. Honeybees, the most abundant pollinator, might partially compensate the loss of wild pollinators in some areas, but our results suggest the need of landscape-scale actions to enhance wild pollinator populations.},
  language  = {en}
}