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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
191

The synthesis and characterisation of metal complexes containing chemically reduced bipyridyl ligand systems

Irwin, Mark Robert Floyd January 2013 (has links)
This thesis describes the synthesis and characterisation of metal complexes that contain chemically reduced bipyridyl ligands. The crystal structures of twenty-six novel complexes are reported alongside detailed discussions on the electronic and spectroscopic effects and trends associated with the different oxidation states within these species. Chapter One introduces the isomers of bipyridine and their redox chemistry, the concept of non-innocent ligands and the spectroscopic techniques that are currently used in determining ligand oxidation states. Subsequently, examples of main group, transition metal, lanthanide and actinide species that contain or may contain reduced forms of the ligand are discussed. Chapter Two details the synthesis and structural characterisation of alkali metal salts of singly and doubly reduced forms of the three commercially available bipyridine isomers. The effects of this reduction are investigated with the aim of developing diagnostic fingerprints for each of the ligand oxidation states. Chapter Three discusses the synthesis of an homologous series of compounds of the form [M(2,2'-bipy)(mes)<sub>2</sub>]<sup>n–</sup> where M = Cr, Mn, Fe, Co, Ni and n = 0, 1. Trends in magnetism, bonding and electronic structure are investigated with reference to theoretical calculations and the diagnostic fingerprints identified in the previous chapter. Chapter Four describes the synthesis and characterisation of three compounds containing the isostructural motif [Zn<sub>2</sub>(4,4'-bipy)(mes)<sub>4</sub>]<sup>n–</sup> where n = 0, 1, 2. Structural and spectroscopic changes are discussed and com- pared to theoretical calculations. Chapter Five contains descriptions of the spectroscopic techniques employed in the above research and synthesis routes to all compounds featured in this thesis.
192

A tale of two spins : electron spin centre assemblies with N@C60 for use in QIP

Farrington, Benjamin Joseph January 2014 (has links)
Quantum information processing (QIP) has the potential to reduce the complexity of many classically ‘hard’ computational problems. To implement quantum information algorithms, a suitable physical quantum computer architecture must be identified. One approach is to store quantum information in the electron spins of an array of paramagnetic N@C<sub>60</sub> endohedral fullerene molecules, using the electron-electron dipolar interaction to permit the formation of the entangled quantum states needed to implement QIP. This thesis explores two different chemical methods to create two-spin centre arrays that contain N@C<sub>60</sub>. The first method uses a double 2,3 dipolar cycloaddition reaction to a dibenzaldehyde-terminated oligo-p-phenylene polyethynylene (OPE) unit , to create an (S<sub>3/2</sub>, S<sub>3/2</sub>) N@C<sub>60</sub>-N@C<sub>60</sub> dimer with a fixed spin centre separation of 2.7 nm. The second approach is via a self-assembly scheme in which a Lewis base functionalised N@C<sub>60</sub> molecule coordinates to an antiferromagnetic metallic ring magnet to form a (S<sub>3/2</sub>, S<sub>3/2</sub>) two-spin centre N@C<sub>60</sub>-Cr<sub>7</sub>Ni system with an inter-spin separation of 1.4 nm. In both systems, a significant perturbation of the electron spin transition energies is observed using CW ESR, this perturbation is shown to be well accounted for by the inclusion of an electron-electron dipolar coupling term in the electron spin Hamiltonians. To create entanglement in an ensemble of two-spin centre molecules, the dipolar coupling interaction must lie within a narrow distribution. To achieve this not only the separation but also the orientation of the inter-spin axis with respect to the applied magnetic field must be controlled for which a method of macroscopic alignment is required. The potential of using a uniaxially drawn liquid crystal elastomer to exert uniaxial order on fullerene dimers is tested, finding that the degree of alignment is insufficient, possibly a result of the propensity for the fullerene molecules to phase separate from the elastomer. This phase separation is shown to restrict N@C<sub>60</sub> phase coherence lifetime to 1.4 µs at 40 K due to instantaneous spin diffusion. The electron spin environment of both N@C<sub>60</sub> and an N@C<sub>60</sub>-C<sub>60</sub> dimer in a polymer matrix is examined using polystyrene as the host matrix. By deuteration of the polystyrene matrix, a maximum phase coherence lifetimes of 48 µs and 21 µs are measured for the N@C<sub>60</sub> and N@C<sub>60</sub>-C<sub>60</sub> dimer, respectively. The concept of reading out the electron spin state of N@C<sub>60</sub> molecules by coupling it to a spin system that can be probed using optically detected magnetic resonance (ODMR) such as an NV- centre has been previously suggested. To this end, the photostability of N@C<sub>60</sub> under 637 nm laser illumination has been examined in solution. The effect of the presence of an atmospheric concentration of oxygen is striking, affording a 57-fold retardation in the photodecomposition of N@C<sub>60</sub> compared to a degassed solution. When ambient oxygen is present, the average number of excitations that are required to cause decomposition is ≈60000. Finally, for future UV photophysics experiments involving N@C<sub>60</sub>, the best solvent to use was found to be decalin, finding that it significantly slowed decomposition of N@C<sub>60</sub> in both ambient and degassed solutions. The conclusions of this work make a significant contribution to the field of QIP with N@C<sub>60</sub>, showing that there is a bright future for N@C<sub>60</sub>.
193

Alkaline earth- and rare earth-transition metal complexes

Blake, Matthew Paul January 2013 (has links)
This Thesis describes the synthesis and characterisation of new alkaline earth- and rare earth-transition metal complexes. Experimental and computational studies were performed to investigate the structure and bonding in these complexes. Their reactivity was also studied. Chapter 1 introduces metal-metal bonded complexes and current alkaline earth- and rare earth-transition metal bonded complexes. Chapter 2 describes experimental and computational studies of new alkaline earth- and lanthanide-Fe complexes possessing the [CpFe(CO)2]- anion. Chapter 3 presents experimental studies of the reduction of Fe3(CO)12 with Ca. Chapter 4 describes experimental and computational studies of new alkaline earth- and lanthanide-Co complexes containing the [Co(CO)3(PR3)]- anion. Chapter 5 presents full experimental procedures and characterising data for the new complexes reported. Appendix describes the attempted synthesis of [Ca{CpRu(CO)2}2(THF)x]y and study by DFT of [CaRp2(THF)3]2 CD Appendix contains .cif files for all new crystallographically characterised complexes described.
194

The development of the concept of episcopacy in the Church of England from the nineteenth to the mid-twentieth centuries

Weishaupt, Steffen January 2013 (has links)
The purpose of this thesis is to examine the Church of England’s understanding of ‘episcopal’ episcopacy and ordained ministry, including their ecclesiological implications and ecumenical consequences. Special attention is given to the refusal of interchangeability of ordained ministers with ‘non-episcopal’ churches (whilst allowing inter-communion), on the grounds that they lacked a ‘historic succession’ of bishops (cf. The Meissen Declaration and Agreement). This claim gives the adjective ‘episcopal’ a denominational, (quasi-)sacramental connotation (hence the inverted commas). Official Anglican statements today claim that the concept of episcopacy in a ‘historic succession’ is and always has been an integral part of ‘Anglican’ teaching as part of its ‘Catholic’, pre-Reformation heritage, whereas it appears that before the nineteenth century the Church of England had been defined largely in territorial and institutional terms. This faced challenges both from without and within, with an increasingly secular and multi-denominational context in Britain (with Non-conformists slowly gaining equal social and political rights) and in the face of the emergence of the Anglican Communion (and ecumenism in the twentieth century). This required the Church of England to forge a distinctive, trans-national, denominational identity for itself and for ‘Anglicanism’ (which can be described as the ‘Anglicanization of the Church of England’). In the first half of the nineteenth century, the English episcopate exercised a more active leadership role (the ‘episcopalization of the Church of England’), creating bishoprics in overseas dependencies and strengthening the influence of the Church of England there and also that of the episcopate (a colonial aspect of the ‘Anglicanization’). In the second half of the nineteenth century the bishops established interchangeability of ministers with formerly English, ‘Episcopal’ churches. This development occurred at the high point of Anglo-Catholic and ritualistic influence (which resulted in a ‘Catholicization of the Church of England’, opposed by Evangelicals and High-churchmen of the pre-Tractarian type). The nature of ‘Anglicanism’ was increasingly interpreted as ‘catholic’/‘Catholic’. In the twentieth century the notion of a ‘historic succession’ of bishops eventually appeared in official documents, whereas earlier statements had been insisting on the ‘historic episcopate’, but open to an understanding in the sense of ‘apostolic succession’ or a divinely instituted or sanctioned, or simply ancient form of government (episcopacy as esse, plene esse or bene esse of church). The eventual adoption of the notion of succession, however, the crucial characteristic of the esse model, meant a ‘theologization’ of Anglican ecclesiology in the late nineteenth and early twentieth centuries with a distinct ‘catholic’ character, which explains the refusal to agree on interchangeability of ministers with ‘Protestant’ churches, now on theological grounds.
195

A phenomenological exploration of the domain and structure of internal marketing

Anosike, Uchenna Paschal January 2008 (has links)
Despite the fact that Internal Marketing (IM) has emerged to capture the interest of academic researchers and management practitioners, there is a surprising absence of empirical study investigating how IM is experienced in the world of practice. This constitutes an impediment to bridging the gap in the holistic understanding of the IM concept. The big question that remains is how to articulate precisely those activities that can be taken to constitute the structure of IM and those that do not. This study aims to bridge this gap by exploring whether the experiences of managers who are implementing IM in their organisations could provide clarity as to the meaning and the constituents structure of IM. This study first undertakes scrutiny of the extant IM literature in an attempt to clarify the multiplicity of terms often associated with IM. The meaning and the constituents structure of IM was investigated via an in-depth qualitative study guided by the principles of phenomenology. This qualitative study is based around open-ended interviews with participants sampled from the UK private and public sector firms. Data was collected and analysed in line with Giorgi’s descriptive phenomenological research praxis. The phenomenological findings indicate nine overlapping elements, namely, internal communication, employee training, reward, empowerment, employee motivation, interdepartmental co-ordination, understanding the organisation, commitment, and top management support that emerged to constitute the experiential structure of IM. Drawing upon these elements, the study offers a conceptual framework of the IM structure. Systematic analytical steps were utilised to ensure the validity of findings.
196

Template directed synthesis of porphyrin nanorings

O'Sullivan, Melanie Claire January 2011 (has links)
This thesis describes supramolecular approaches to porphyrin nanorings. Cyclic porphyrin arrays resemble natural light harvesting systems, and it is of interest to probe the photophysical effects of bending the porphyrin aromatic π-system. A general overview of the synthesis and photophysical properties of porphyrins and their arrays is carried out in Chapter 1. The electronic structure of porphyrins is examined, and how conformational effects in oligomers, such as inter-porphyrin torsional angle and backbone bending influence the π-conjugation pathway. The structures of light harvesting complexes are discussed. Chapter 2 describes the design and synthesis of a complementary 12-armed template designed to coordinate linear porphyrin oligomers in the correct conformation for cyclisation to give a cyclic porphyrin dodecamer. Chapter 3 demonstrates two approaches to a cyclic porphyrin dodecamer ring. Firstly, a classical templating approach using the 12-armed template is described. The limitations of this approach in the quest for larger nanorings are discussed. Vernier templating, which utilises a mismatch in the number of binding sites between a ligand and its receptor is introduced as a general strategy to the synthesis of large nanorings. This is demonstrated by the synthesis of cyclic dodecamer from a linear porphyrin tetramer and a hexadentate template via a figure-of-eight intermediate. The general utility of the Vernier method to large nanorings is explored in Chapter 4 with steps towards the synthesis of a cyclic tetracosamer, consisting of 24 porphyrin subunits. In preliminary experiments, an improved route to the cyclic porphyrin octamer is described. Finally, the photophysical properties of the nanoring series are explored in Chapter 5 as a function of size and conformation. Femtosecond photoluminescence spectroscopy shows that even in cyclic dodecamer, exciton delocalisation over the entire porphyrin backbone occurs on a sub-picosecond timescale, and parallels are drawn with the dynamics of natural light harvesting complexes.
197

New main group and rare earth complexes and their applications in the ring-opening polymerisation of cyclic esters

Cushion, Michael Gregory January 2011 (has links)
This Thesis describes the synthesis and characterisation of new Main Group and Rare Earth alkyl, amide, alkoxide and borohydride complexes and their use as catalysts for the ring-opening polymerisation (ROP) of &epsilon;-caprolactone and rac-lactide. <strong>Chapter 1</strong> introduces ROP from an industrial and academic perspective, as well as polymer characterisation techniques. A literature review is given, with an emphasis placed on Main Group catalysts. <strong>Chapter 2</strong> describes the synthesis and characterisation of new homo- and hetero-scorpionate Main Group complexes. An introduction to homo- and hetero-scorpionate ligands is given, as well as a discussion of the ε-caprolactone and rac-lactide ROP activity displayed by the new complexes. <strong>Chapter 3</strong> describes the synthesis and characterisation of new neutral and cationic Main Group borohydride complexes supported by the tris(pyrazolyl)methane and tris(pyrazolyl)hydroborate ligands. A review of borohydride complexes is also given. The ε-caprolactone and rac-lactide ROP activity shown by the complexes presented is also discussed. <strong>Chapter 4</strong> describes the synthesis and characterisation of new mono- and di-cationic yttrium complexes supported by the tris(pyrazolyl)methane and triazacyclononane ligands. An introduction to the synthesis of neutral and cationic Rare Earth complexes is given. An overview of immortal ROP is also provided. The activity of the new complexes towards the immortal ROP of rac-lactide is also discussed. <strong>Chapter 5</strong> contains experimental details and characterising data for the new complexes reported in this thesis. CD Appendix</strong> contains .cif files for all of the new crystallographically characterised complexes.
198

Investigating the chemistry of cationic rhodium bisphosphine complexes : comparing reactivity in the solid state with solution

Pike, Sebastian David January 2014 (has links)
This thesis describes the synthesis and characterisation of a series of cationic rhodium bis-phosphine complexes. The reactivity of these new complexes in the solid-state and in solution is reported. In <b>Chapter 2</b> the synthesis of a series of rhodium bis-phosphine diene complexes is presented and the reactions of these complexes with hydrogen in the solid-state are investigated. Several examples of zwitterionic complexes coordinating the [BAr<sup>F</sup>4]<sup>─</sup> anion are produced by hydrogenation. A rare example of a sigma-alkane complex, [Rh(<sup>i</sup>Bu<sub>2</sub>PCH<sub>2</sub>CH<sub>2</sub>P<sup>i</sup>Bu<sub>2</sub>)(eta<sup>2</sup>-<sub>CH</sub>-eta<sup>2</sup>-<sub>CH</sub>-NBA][BAr<sup>F</sup>4]<sup>─</sup], is also formed in the solid-state, by a single crystal to single crystal transition driven by hydrogen. This complex is crystallographically characterised and displays two short Rh∙∙∙H−C sigma-interactions. Deuteration studies indicate that the agostic complex [Rh(<sup>i</sup>Bu<sub>2</sub>PCH<sub>2</sub>CH<sub>2</sub>P<sup>i</sup>Bu<sub>2</sub>)(eta<sup>2</sup>-<sub>CH</sub>-eta<sup>2</sup>-<sub>CH</sub>-NBE][BAr<sup>F</sup>4] may form as a short lived intermediate prior to the formation of the sigma-alkane complex. The temporal evolution of the solid-state hydrogenation reactions is monitored by powder X-ray diffraction methods. In <b>Chapter 3</b> the C−X activation of various aryl halides using the [Rh(<sup>i</sup>Bu<sub>2</sub>PCH<sub>2</sub>CH<sub>2</sub>P<sup>i</sup>Bu<sub>2</sub>)]<sup>+</sup> fragment is reported. The 'ligand innocence' of the phosphine with respect to intramolecular C−H activation is also discussed. A rare example of C−X activation in the solid-state is presented, which shows the formation of an isomer that is not observed by analogous solution routes. <b>Chapter 4</b> investigates solid-state ligand exchange reactions using ethene, butadiene, CO and NH3 gases. A solid-state transfer dehydrogenation reaction is reported within single crystals of [Rh(<sup>i</sup>Bu<sub>2</sub>PCH<sub>2</sub>CH<sub>2</sub>P<sup>i</sup>Bu<sub>2</sub>)(C<sub>2</sub>H<sub>4</sub>)<sub>2</sub>][BAr<sup>F</sup>4]. H/D exchange of NH3 can also occur in the solid state in the bis-ammonia complex [Rh(<sup>i</sup>Bu<sub>2</sub>PCH<sub>2</sub>CH<sub>2</sub>P<sup>i</sup>Bu<sub>2</sub>)(NH<sub>3</sub>)<sub>2</sub>][BAr<sup>F</sup>4]. A variety of rhodium complexes are tested as heterogeneous catalysts for the hydrogenation of ethene and the isomerisation of butene. In <b>Chapter 5</b> the binding affinity of a variety of fluorinated arenes to rhodium bis-phosphine fragments is presented using ESI-MS methods. The dependence upon the arene substituents, phosphine substituents and phosphine bite angle are discussed.
199

Synthesis and characterisation of permethylpentalene complexes and permethylpentalene derivatives

Binding, Samantha Carys January 2015 (has links)
This thesis expands the scope for using the permethylpentalene ligand and its precursors in the synthesis of organometallic complexes. <strong>Chapter one</strong> begins with a brief review of linked metallocenes, with which multimetallic compounds bridged by pentalene ligands have often been compared, followed by a comprehensive review of the routes used to make pentalenes and substituted pentalenes. Organometallic compounds of pentalenes are introduced, with a focus on bimetallic systems. <strong>Chapter two</strong> explores the diversification of substituents added to the permethylpentalene (Pn*) precursor WeissH<sub>4</sub>, to include ethyl and isopropyl groups. Low-symmetry mono-, di-, tri- and tetraalkylated products are formed, eight such organic molecules have been identified by NMR spectroscopy, and two characterised crystallographically. It has been demonstrated that subsequent hydrolysis and decarboxylation of two of these products produces low-symmetry alkylpentalene precursors. The chapter concludes with discussions on the selectivity exhibited in these reactions, and the assignment of stereochemistry. <strong>Chapter three</strong> describes the synthesis of the first homoleptic double metallocene complex of iron. Fe<sub>2</sub>Pn*<sub>2</sub> has been characterised by X ray diffraction, and cyclic voltammetry studies demonstrate four accessible oxidation states (-1, 0, +1, +2). Magnetic measurements in the solid and solution state reveal an unusual triplet configuration, and DFT calculations indicate the origin of a high magnetic moment likely resides in unquenched orbital angular momentum contributions from SOMOs which have metal d character. Fe<sub>2</sub>Pn*<sub>2</sub> is EPR silent at 5, 40, and 300 K both in solution and the solid state, suggesting a large zero-field splitting parameter. The reaction of the di-iron complex with carbon monoxide, ethylene and H2 is reported; the bimetallic CO adduct, Fe<sub>2</sub>(&mu; &eta;<sup>5</sup>,&eta;<sup>3</sup> Pn*)(&mu; &eta;<sup>5</sup>,&eta;<sup>1</sup> Pn*)(CO)<sub>2</sub>, has been crystallographically characterised, and contains a highly distorted allylic bonding motif, which to the author’s knowledge is believed to be unique among iron complexes. <strong>Chapter four</strong> discusses the interaction of the bidentate Pn* ligand in anti bimetallic fused metallocenes. A new ligand exchange route has been developed to access the complexes (MCp)<sub>2</sub>Pn* (M = Co, Ni), and the isostructural complexes (MCp*)<sub>2</sub>Pn* have been made for M = Fe, Co, Ni by salt metathesis reactions. All five complexes have been characterised by single crystal X-ray crystallography, and have diamagnetic ground states in solution in common with their Pn bridged analogues. Variable temperature NMR studies reveal a spin-equilibrium between S = 0 and S = 1 in the dinickel complexes. DFT calculations reproduce the spin states found, and suggest the distortion towards &eta;<sup>3</sup> coordination observed on crossing from Fe, to Co, to Ni, results from population of orbitals with M―bridgehead antibonding character. The electronic structures show it is important to draw comparisons between isoelectronic linked metallocenes. Electrochemical studies on the diiron, dicobalt, and (NiCp)<sub>2</sub>Pn* complexes reveal at least three redox events for each. <strong>Chapter five</strong> documents the successful synthesis and characterisation of monometallic complexes of iron and manganese with Pn*H ligands. The isostructural complexes Fe(Pn*H)<sub>2</sub> and Mn(Pn*H)<sub>2</sub> can have been characterised crystallographically, and are potential precursors for accessing heterometallic, and multimetallic complexes. Mn(Pn*H)<sub>2</sub> is a rare example of a manganese sandwich compound and magnetic studies on a single isomer in the solution and solid states suggest it adopts intermediate spin states of S = 2 in solution, and S = 3/2 in the solid state. <strong>Chapter six</strong> gives experimental details for all syntheses and studies described in the preceding chapters. <strong>Chapter seven</strong> provides characterising data for all new compounds. Fitting data for VT NMR and SQUID studies are provided in the <strong>appendix</strong> at the end of this thesis. Crystallographic data in the form of .cif files, DFT output files, and raw SQUID data, can be found in the <strong>electronic appendix</strong>.
200

Padrões de diversidade em comunidades de aves relacionadaos a varáveis de habitat em campos temperados do sudeste da América do Sul

Dias, Rafael Antunes January 2013 (has links)
Indivíduos, populações e espécies tendem a usar e selecionar habitats de modo não-aleatório. Consequentemente, a perda e a degradação de habitats geram impactos distintos sobre os organismos dependendo de seus atributos. Os efeitos da perda de habitat são claros – os organismos são eliminados ou desalojados por falta de habitat ou baixo sucesso reprodutivo. As consequências da degradação de habitat são mais sutis, e resultam na incapacidade de um ecossistema sustentar determinadas espécies. Como a perda e a degradação de habitat reduzem a disponibilidade de nichos, espera-se que táxons ecologicamente especializados e com requerimentos estreitos de nicho sejam mais propensos à extinção que generalistas. Organismos que são negativamente afetados por perda e degradação de habitat em geral exibem porte muito grande ou muito pequeno, baixa mobilidade, baixa fecundidade, reduzido recrutamento e estreitos requerimentos de nicho. Campos temperados constituem ambientes particularmente afetados por perda e degradação de habitat. No sudeste da América do Sul, como em muitas outras regiões do planeta, a expansão da agricultura e silvicultura são os principais responsáveis pela perda de habitat campestre. Os remanescentes de vegetação natural são usados para criação de gado, estando sujeitos à degradação pelo sobrepastejo, pisoteio e técnicas de manejo. Avaliar como a perda e degradação de habitat afetam a diversidade de organismos campestres é vital para o desenvolvimento de estratégias de conservação e manejo. A presente tese tem por objetivo investigar como a degradação e perda de habitat induzidas pela pecuária e silvicultura afetam a diversidade e a composição das comunidades de aves. Inicialmente, exploramos as relações entre variáveis de habitat e a composição da comunidade de aves num gradiente de altura da vegetação determinado por pastejo em campos litorâneos do Rio Grande do Sul. Posteriormente, avaliamos como variações no relevo interagem com variáveis de habitat e afetam a diversidade de aves em áreas de pecuária na Campanha gaúcha. Finalmente, avaliamos de que forma a perda de habitat resultante do estabelecimento de plantações industriais de celulose em áreas de campo afeta a composição de comunidades de aves campestres. Nossos resultados demonstram que a degradação de habitat decorrente do manejo de gado em campo nativo afeta a comunidade de aves de forma diferencial. Aves adaptadas a campos ralos ou generalistas tendem a ser beneficiadas pelo pastejo, ao passo que as espécies associadas à vegetação alta e densa são desfavorecidas. As variações na topografia reduzem os impactos da degradação de habitat nos campos. Essas variações interagem com o habitat e afetam de forma diferencial os distintos componentes da diversidade. Por outro lado, a perda de habitat decorrente da silvicultura gera um impacto de maior magnitude, alterando a composição das comunidades de aves e favorecendo aves não-campestres. Nesse contexto, impedir que novas áreas de campo nativo sejam convertidas em plantações de árvores passa a ser imperativo. Embora o manejo do gado aumente a diversidade em nível de paisagem ao criar um mosaico de manchas de vegetação de alturas distintas, maior atenção deve ser dada à manutenção e recuperação de formações densas de herbáceas de grande porte. Isso somente pode ser assegurado através de mudanças no regime do pastejo ou do desenvolvimento de técnicas de manejo alternativas. / Individuals, populations and species tend to select habitats in a non-random way. Consequently, habitat loss and degradation will have different impacts on organisms according to their traits. The effects of habitat loss are straightforward – organisms are eliminated or displaced because of the inexistence of adequate habitat or of low breeding success. Effects of habitat degradation are more subtle and result in the reduction of the capacity of an ecosystem to support some subsets of species. Since habitat loss and degradation reduce niche availability, ecologically specialized taxa with narrow niche requirements are expected to be more extinction prone than habitat generalists. Temperate grasslands have been strongly impacted by habitat loss and degradation. In southeastern South America, the expansion of agriculture and industrial pulpwood plantations are the main sources of habitat loss. Remnants of natural grassland vegetation are used for livestock ranching, being subject to habitat degradation from overgrazing, trampling and inadequate management techniques. The evaluation of how habitat loss and degradation affect the diversity of grassland organisms is vital for the development of management and conservation techniques. The main goal of this thesis is to evaluate how habitat degradation and loss related to cattle ranching and pulpwood plantations affect the diversity and composition of bird communities. We began by exploring the relationship between habitat variables and the composition of the bird community along a gradient of vegetation height determined by grazing in coastal grasslands of the state of Rio Grande do Sul. We then assessed how variations in the relief interact with habitat variables e affect the diversity of birds in rangelands of the Campanha gaúcha. Finally, we evaluated how habitat loss related with grassland afforestation for pulpwood plantations affects the composition of grassland bird communities. Our results demonstrate that habitat degradation resulting from livestock ranching in natural grasslands affects bird communities in a differential way. Birds adapted to stunted grasslands or habitat generalists tend to benefit from grazing, whereas tall-grass specialists are negatively affected. Variations in topography are responsible for reducing the impacts of habitat degradation in grasslands. These variations interact with habitat and have a differential effect on distinct components of diversity. On the other hand, the magnitude of the impact of habitat loss from afforestation is larger, altering the composition of bird communities and favoring a series of non-grassland species. In this sense, protecting remaining grasslands from afforestation is imperative. Although cattle ranching increases diversity at the landscape level by creating a mosaic of vegetation patches of different height, more attention should be given in maintaining and recovering dense formations of tall grassland plants. This can only be achieved by changing grazing regimes or developing alternative management techniques.

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