New Chiral Auxiliaries For The [3+2]-Cycloaddition Of Nonstabilised Azomethine Ylides

The [3+2]-cycloaddition reaction of nonstabilised azomethine ylides to alkenes is a valuable synthetic method for the assembly of functionalised pyrrolidines. However, there are only a few examples of such eye lo add it ions being successfully performed with an unstabilised azomethine ylide that has been tethered to a removable chiral auxiliary. Most of the reactions studied so far have exhibited only modest levels of diastereoselectivity (ca. 60 % d.e.), and in every case, destruction of the chiral auxiliary has proven necessary before the newly fashioned chiral pyrrolidine cycloadduct could be liberated. In the first part of this thesis, the potential utility of optically pure 1,1-dialkylhydrazines as chiral auxiliaries for nonstabilised azomethine ylide cycloadditions to alkenes has been investigated. While the preparation of several chiral 1,1-dialkylhydrazines was carried out successfully, the formation of the N-amino azomethine ylide precursors from these hydrazines failed, occasionally giving interesting unwanted and unexpected by-products. The second part of this thesis focuses on the evaluation of several new chiral auxiliaries as stereochemical control elements for 1,3-dipolar cycloadditions of azomethine ylides to alkenes. This work failed with some auxiliaries and was partially successful with others. The successful [3+2]-cycloaddition reactions were all performed with dimethyl fumarate as the dipolarophile, but afforded little or no stereoselectivity. The cleavage of the newly-created pyrrolidine systems from these auxiliaries under various conditions also proved to be unsuccessful. During this work a new method for the preparation of 1,1-dialkyIhydrazines by the reduction of N-nitroso precursors was discovered. The potential utility of this method has been evaluated, and the results are discussed in Chapter 4

The restoration of plant pollinator interactions

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The restoration of ecological interactions: plant-pollinator networks on ancient and restored heathlands

1. Attempts to restore damaged ecosystems usually emphasize structural aspects of biodiversity, such as species richness and abundance. An alternative is to emphasize functional aspects, such as patterns of interaction between species. Pollination is a ubiquitous interaction between plants and animals. Patterns in plant-pollinator interactions can be analysed with a food web or complex-systems approach and comparing pollination webs between restored and reference sites can be used to test whether ecological restoration has taken place. 2. Using an ecological network approach, we compared plant-pollinator interactions on four pairs of restored and ancient heathlands 11 and 14 years following initiation of restoration management. We used the network data to test whether visitation by pollinators had been restored and we calculated pollinator importance indices for each insect species on the eight sites. Finally, we compared the robustness of the restored and ancient networks to species loss. 3. Plant and pollinator communities were established successfully on the restored sites. There was little evidence of movement of pollinators from ancient sites onto adjacent restored sites, although paired sites correlated in pollinator species richness in both years. There was little insect species overlap within each heathland between 2001 and 2004. 4. A few widespread insect species dominated the communities and were the main pollinators. The most important pollinators were typically honeybees (Apis mellifera), species of bumblebee (Bombus spp.) and one hoverfly species (Episyrphus balteatus). The interaction networks were significantly less complex on restored heathlands, in terms of connectance values, although in 2004 the low values might reflect the negative relationship between connectance and species richness. Finally, there was a trend of restored networks being more susceptible to perturbation than ancient networks, although this needs to be interpreted with caution. 5. Synthesis and applications. Ecological networks provide a powerful tool for assessing the outcome of restoration programmes. Our results indicate that heathland restoration does not have to occur immediately adjacent to ancient heathland for functional pollinator communities to be established. Moreover, in terms of restoring pollinator interactions, heathland managers need only be concerned with the most common insect species. Our focus on pollination demonstrates how a key ecological service can serve as a yardstick for judging restoration success

The structure and robustness of nocturnal Lepidopteran pollen-transfer networks in a Biodiversity Hotspot

1. The role of nocturnal moths within plant-pollinator networks is poorly understood but could be important in the context of declining biodiversity and the ecosystem services they provide. 2. For the first time, this study examined the role of moths as pollen vectors in the Mediterranean Biodiversity Hotspot. Light traps were used to sample moths in SW Portugal in 2010. The pollen on moth head parts was collected, identified, and counted to construct a nocturnal pollen-transfer and flower-visitor network. 3. A total of 257 moths belonging to 95 species were captured in 11 trapping sessions in 2010; 196 moths (76%) carried pollen and the total number of pollen grains counted and identified was 9064. 4. The pollen-transfer network exhibited a high degree of selectivity (H20) but low robustness when the most-to-least connected plants were made extinct in the network. The flower-visitor network (based on the incidences of interactions by individual moths), however, exhibited high linkage density and was generally more robust to simulated plant or moth extinction. 5. Including nocturnal moths in plant–pollinator networks will provide a better understanding of their robustness to species extinctions due to environmental change as well as the impacts on ecosystem structure and functioning. Nocturnal pollen–transfer networks could be developed for identifying key species for targeted conservation

Potential landscape-scale pollinator networks across Great Britain: structure, stability and influence of agricultural land cover

Understanding spatial variation in the structure and stability of plant-pollinator networks, and their relationship with anthropogenic drivers, is key to maintaining pollination services and mitigating declines. Constructing sufficient networks to examine patterns over large spatial scales remains challenging. Using biological records (citizen science), we constructed potential plant-pollinator networks at 10km resolution across Great Britain, comprising all potential interactions inferred from recorded floral visitation and species co-occurrence. We calculated network metrics (species richness, connectance, pollinator and plant generality) and adapted existing methods to assess robustness to sequences of simulated plant extinctions across multiple networks. We found positive relationships between agricultural land cover and both pollinator generality and robustness to extinctions under several extinction scenarios. Increased robustness was attributable to changes in plant community composition (fewer extinction-prone species) and network structure (increased pollinator generality). Thus, traits enabling persistence in highly agricultural landscapes can confer robustness to potential future perturbations on plant-pollinator networks

Costing conservation: an expert appraisal of the pollinator habitat benefits of England’s entry level stewardship

Pollination services provided by insects play a key role in English crop production and wider ecology. Despite growing evidence of the negative effects of habitat loss on pollinator populations, limited policy support is available to reverse this pressure. One measure that may provide beneficial habitat to pollinators is England’s entry level stewardship agri-environment scheme. This study uses a novel expert survey to develop weights for a range of models which adjust the balance of Entry Level Stewardship options within the current area of spending. The annual costs of establishing and maintaining these option compositions were estimated at £59.3–£12.4 M above current expenditure. Although this produced substantial reduction in private cost:benefit ratios, the benefits of the scheme to pollinator habitat rose by 7–140 %; significantly increasing the public cost:benefit ratio. This study demonstrates that the scheme has significant untapped potential to provide good quality habitat for pollinators across England, even within existing expenditure. The findings should open debate on the costs and benefits of specific entry level stewardship management options and how these can be enhanced to benefit both participants and biodiversity more equitably

Ecosystem restoration strengthens pollination network resilience and function.

Land degradation results in declining biodiversity and the disruption of ecosystem functioning worldwide, particularly in the tropics. Vegetation restoration is a common tool used to mitigate these impacts and increasingly aims to restore ecosystem functions rather than species diversity. However, evidence from community experiments on the effect of restoration practices on ecosystem functions is scarce. Pollination is an important ecosystem function and the global decline in pollinators attenuates the resistance of natural areas and agro-environments to disturbances. Thus, the ability of pollination functions to resist or recover from disturbance (that is, the functional resilience) may be critical for ensuring a successful restoration process. Here we report the use of a community field experiment to investigate the effects of vegetation restoration, specifically the removal of exotic shrubs, on pollination. We analyse 64 plant-pollinator networks and the reproductive performance of the ten most abundant plant species across four restored and four unrestored, disturbed mountaintop communities. Ecosystem restoration resulted in a marked increase in pollinator species, visits to flowers and interaction diversity. Interactions in restored networks were more generalized than in unrestored networks, indicating a higher functional redundancy in restored communities. Shifts in interaction patterns had direct and positive effects on pollination, especially on the relative and total fruit production of native plants. Pollinator limitation was prevalent at unrestored sites only, where the proportion of flowers producing fruit increased with pollinator visitation, approaching the higher levels seen in restored plant communities. Our results show that vegetation restoration can improve pollination, suggesting that the degradation of ecosystem functions is at least partially reversible. The degree of recovery may depend on the state of degradation before restoration intervention and the proximity to pollinator source populations in the surrounding landscape. We demonstrate that network structure is a suitable indicator for pollination quality, highlighting the usefulness of interaction networks in environmental management

Declining resilience of ecosystem functions under biodiversity loss

The composition of species communities is changing rapidly through drivers such as habitat loss and climate change, with potentially serious consequences for the resilience of ecosystem functions on which humans depend. To assess such changes in resilience, we analyse trends in the frequency of species in Great Britain that provide key ecosystem functions-specifically decomposition, carbon sequestration, pollination, pest control and cultural values. For 4,424 species over four decades, there have been significant net declines among animal species that provide pollination, pest control and cultural values. Groups providing decomposition and carbon sequestration remain relatively stable, as fewer species are in decline and these are offset by large numbers of new arrivals into Great Britain. While there is general concern about degradation of a wide range of ecosystem functions, our results suggest actions should focus on particular functions for which there is evidence of substantial erosion of their resilience

Exploring the predation of UK bumblebees (Apidae, Bombus spp.) by the invasive pitcher plant Sarracenia purpurea: examining the effects of annual variation, seasonal variation, plant density and bumblebee gender

Invasive carnivorous plant species can impact the native invertebrate communities on which they prey. This article explores the predation of native UK bumblebees (Bombus spp.) by the invasive pitcher plant species Sarracenia purpurea and discusses the potential effect of S. purpurea on native bumblebees. Specifically, it evaluates whether the extent to which bumblebees are captured varies (i) over successive years, (ii) across June and July, (iii) with density of distribution of pitchers or (iv) with bumblebee gender. Pitcher contents were examined from an established population of Sarracenia purpurea growing in Dorset, UK. Results show that the total extent to which bumblebees were captured differed over the years 2012–2014 inclusive. A 1-year study in 2013 showed that more bumblebees were caught in July than in June and more bumblebees were captured when pitchers grew at high density. Results from 2013 also showed that more pitchers caught more than one bumblebee than would be expected based on a normal probability distribution and that this phenomenon affects female and male bumblebees equally. We discuss possible reasons for these results including that the bumblebees may be using S. purpurea as a resource. Further work is required to establish the exact underpinning mechanisms and the relative roles of plant and bumblebee behaviour within the relationship. Such interaction complexity may have consequences for consideration in invasive carnivorous plant management