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1
Barraclough, Timothy Giles. "Biological correlates of species diversity". Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320144.
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Senft, Amanda Ruth Peet R. K. "Species diversity patterns at ecotones". Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2009. http://dc.lib.unc.edu/u?/etd,2210.
Testo completoAbstract (sommario):
Thesis (M.S.)--University of North Carolina at Chapel Hill, 2009.Title from electronic title page (viewed Jun. 26, 2009). "... in partial fulfillment of the requirements for the degree of Masters of Science in the Department of Biology." Discipline: Biology; Department/School: Biology.
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Platt, Jacqueline Berengaria. "Habitat complexity and species diversity in rivers". Thesis, Cardiff University, 2011. http://orca.cf.ac.uk/23242/.
Testo completoAbstract (sommario):
1. Rivers are highly structured ecosystems in which habitat complexity and heterogeneity are postulated to affect species diversity and abundance. However, the exact links between habitat structure and organisms such as macro-invertebrates remain poorly understood. 2. Field surveys at the patch and reach scale were combined with a field experiment in the Rivers Wye and Usk, Wales, to: i) quantify variations in habitat complexity and heterogeneity among habitats and river sections, ii) assess their influence on macro-invertebrates, iii) separate the ecological effects of confounding physical factors and iv) determine whether habitat type and heterogeneity promote nestedness of assemblages. 3. At the patch scale, surface complexity but not habitat heterogeneity increased macro-invertebrate diversity, richness and abundance independently of surface area, but only when habitat type was ignored. Surface complexity and heterogeneity were minor determinants of variations in macro-invertebrates among habitat types. 4. A field experiment involving baskets containing cobbles, pebbles, gravel or 50:50 mixtures revealed that flow type explained significant variations in macro-invertebrate richness, abundance and composition, and appeared to filter organisms based on their body size. Surface complexity and interstitial volume had no ecological effect, implying that differences in assemblages among mineral habitats may result from flow-related effects. 5. Macro-invertebrate assemblages occurring in some mineral habitats, typically with lower macro-invertebrate diversity, richness, abundance and trait diversity, appeared to be nested sub-sets of those occurring in some organic habitats. Nested assemblages had reduced trait diversity and altered trait representation. River sections containing fewer habitats supported assemblages of lower abundance, which appeared to be weakly nested sub-sets of those in heterogeneous sections. 6. Habitat complexity and heterogeneity are concluded to have consistently weak effects on macro-invertebrates at the scales studied. In contrast, habitat type and flow type affected macro-invertebrate assemblage composition, structure, and traits, with important implications for river management and conservation.
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Davies, Thomas Jonathan. "Environmental energy and species diversity in flowering plants". Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408927.
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Morath, Simon. "Effects of tree species diversity on insect herbivory". Thesis, Royal Holloway, University of London, 2013. http://repository.royalholloway.ac.uk/items/916c671f-79af-41eb-99b1-df69faa84961/1/.
Testo completoAbstract (sommario):
It is generally believed that tree species growing in mixed forest stands are less susceptible to insect herbivore damage than if grown in monocultures, but previous studies have been largely observational and focussed mainly on tree species richness effects. In this thesis, I examined effects of three components of forest diversity (tree species richness, intraspecific genotypic diversity and functional diversity) on insect herbivores using three long-term forest diversity experiments in Finland and Germany. I have also explored the sources of variation in and the mechanisms behind the effects of tree diversity on insect herbivores. I found that all three components of forest diversity significantly influenced insect herbivore abundance and damage. Tree species richness effects depended on the insect herbivore feeding guild, but also changed within season and between years. As a result, silver birch (Betula pendula) experienced both associational resistance (reduced damage in mixed stands) and associational susceptibility (higher damage in mixed stands) to different insect herbivores and in some instances this altered temporally. In contrast, tree species richness effects on insect herbivory were spatially consistent and not mediated by tree size (physical apparency), physical properties of leaves or natural enemies. Interestingly, tree species richness and genotypic diversity had opposite effects on leaf miners; leaf miner abundance and species richness were lower in species-rich stands, but higher in mixtures containing several genotypes of silver birch. To test the effects of tree functional diversity, I created a functional diversity index based on constitutive emissions of monoterpenes and isoprene by different tree species and showed that tree species which emitted low levels of volatiles experienced associational resistance in stands with high diversity of volatile emissions. This suggests that increasing chemical complexity in mixed stands may interfere with host finding ability of herbivores.
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Nicholson, Wendy Elizabeth. "Increasing plant species diversity in contaminated upland grassland". Thesis, University of Newcastle Upon Tyne, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275503.
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Berens, Jeffrey David. "Morphological Differences and Diversity of Small Mammal Species". Thesis, North Dakota State University, 2016. https://hdl.handle.net/10365/27710.
Testo completoAbstract (sommario):
Small mammals play important roles in ecosystems, but are often overlooked due to their small size and plentiful abundance. Two studies evaluated the morphological differences and diversity of small mammal species based on how they react to different environmental conditions. The first study analyzed the morphological differences of skulls between and within two species of Peromyscus species due to differences in shape, size, and geographic position. This study also determined if landmark-based geometric morphometrics could reliably discriminate between the two species. The second study analyzed small mammal diversity and abundance due to differences in microhabitat conditions in an endangered ecosystem: tallgrass prairie. Small mammals are an important food source to other vertebrate and also help regulate vegetation composition in the tallgrass prairie ecosystem. Results of both studies could help future studies identify how different variables affect small mammal morphology and diversity.
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Gutiérrez, Lucía. "Genetic diversity in cultivated and wild Hordeum species". [Ames, Iowa : Iowa State University], 2008.
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Posthumus, Erin Elizabeth. "Do Red Squirrel Middens Promote Vertebrate Species Diversity?" Thesis, The University of Arizona, 2013. http://hdl.handle.net/10150/294022.
Testo completoAbstract (sommario):
The modifications animals make to their environments can be critical to species diversity. Red squirrels (Tamiasciurus hudsonicus) create large piles of conifer cone debris (middens) and are hypothesized to function as a keystone species due to positive associations between middens and other vertebrate species. We assessed vegetation and landscape structure at middens with a resident red squirrel for varying consistencies over the prior 5 years and surveyed mammals and birds at the community and population level. After accounting for vegetation and landscape characteristics, red squirrel-created resources positively influenced species richness of medium and large mammals and ground foraging birds, abundance of deer mice (Peromyscus maniculatus) and ground foraging birds, and activity of cliff chipmunks (Tamias dorsalis). Increased knowledge of the interaction strength of the red squirrel with its environment may be used to inform decisions in forest management and restoration and offer insight on the conservation value of larderhoarding mammals.
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Cooper, Fiona Mary Phillips. "Geographic distribution and genetic diversity of black poplar". Thesis, University of Nottingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246878.
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Corum, Aaron K. "Sixteen valence-electron species containing boron structural diversity abounds /". Diss., Columbia, Mo. : University of Missouri-Columbia, 2005. http://hdl.handle.net/10355/4303.
Testo completoAbstract (sommario):
Thesis (M.S.)--University of Missouri-Columbia, 2005.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (July 13, 2006) Includes bibliographical references.
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Seipel, Timothy Fridolin. "Plant Species Diversity in the Sagebrush Steppe of Montana". Thesis, Montana State University, 2006. http://etd.lib.montana.edu/etd/2006/seipel/SeipelT1206.pdf.
Testo completoAbstract (sommario):
Sagebrush (Artemisia tridentata) is abundant in Montana and is an obvious part of an assemblage of plant species.This community of plants; the sagebrush steppe contains a mixture of grasses, early and late season forbs and shrubs. It is found in semi-arid valleys and plains of Montana and the intermountain western United States, and has received much research attention regarding increasing livestock forage, or of wildlife's dependence on the sagebrush steppe plant communities.Yet, little information on plant species diversity exists. This thesis was undertaken to describe the plant species diversity in three intact sagebrush steppe sites in Montana. The sites were located in Gallitan and Phillips counties. An average of 130 species was found at each site documenting the high levels of diversity that exist in local communities. Diversity measures were similar yet the dissimilarity among sites was high, this could reflect the high diversity of plant species in sagebrush steppe. Of the species recorded none had a restricted range, and this may represent a high rate of migration among local communities. Contrary to a designation as mixed grass prairie at the Phillips county site we found most species representative of the sagebrush steppe and areas of the Great Basin, and the site may be better classified as sagebrush steppe. Introduced plant species were found at all sites. The Burke Park site located in the city of Bozeman has the greatest diversity and abundance of introduced species. The most abundant species were introduced forage grasses. Our results also found that introduced species were negatively associated with the distance to road or trail.This is consistent with other findings that implicate human population density and disturbance as determinants of introduced plant diversity. The implication that human related disturbance and transport of popagules are causes of introduced plant establishment highlights the need for prevention of widespread destruction of sagebrush steppe.
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Noyszewski, Andrzej Krzysztof. "Mitochondrial Sequence Diversity Among Alloplasmic and Euplasmic Triticum Species". Diss., North Dakota State University, 2013. https://hdl.handle.net/10365/27020.
Testo completoAbstract (sommario):
Four mitochondrial genomes of Triticum species were sequenced and annotated: 1) (lo) durum mitochondrial genome, which is an alloplasmic line with Triticum longissimum(SS) cytoplasm and T. turgidum (AABB) nucleus, 2) T. longissimum, 3) T. turgidum and 4) T. tauschii (DD). Comparison showed major differences in atp6, nad9, nad6, rps19-p, cob and cox2 genes among all four species. Additionally, species-specific ORFs were also identified. A single nucleotide polymorphism search within known genes showed that the alloplasmic line differs from the two parental lines by six nucleotides in the cox3, mttB, rps2, rps4 and rps13 genes. We were able to recognize mitochondrial heteroplasmy based on single nucleotide variation (SNV) and regions of high SNV density within a given species. Structural differences between T. turgidum, (lo) durum and T. longissimum mitochondrial genomes were observed; however, conserved gene blocks and gene pairs among these species were identified. Three possible recombination events in gene blocks I, V and VI were recognized. We observed differences in the alloplasmic line, compared to its parental lines in: sequence, predicted genes, single nucleotide polymorphism (SNP) and genome structure. These facts support the hypothesis of the accelerated evolution of the mitochondrial genome when transferred into alien nuclear background. We also found that major gene changes recognized here appear to be common among Triticum species. Based on sequence assembly, we report full mitochondrial sequence of T. turgidum. We recognized 40 SNP differences compared to the T. aestivum mitochondrial genome, where 5 SNPs were found in known mitochondrial genes: rps1, rps2, cox3 and ccmFN. The T. longissimum and T. tauschii share highly similar genomes in structure and content, different only at the level of SNVs. A method to establish phylogenetic relationships based on mitochondrial genome sequence is proposed using differences in reference assembly with a common mitochondrial backbone sequence. We confirm conservation of the mitochondrial gene content within Triticum species. These results create background to explore the role of mitochondrial genes in conditioning nuclear cytoplasmic incompatibility in a wide range of Triticum alloplasmic lines and also deepen our understanding of evolutionary relationships that exist in the Triticum genus.US Army Research Office
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Carvalho, Maria João Mendes de. "Diversity of Aeromonas species from different environments in Portugal". Doctoral thesis, Universidade de Aveiro, 2010. http://hdl.handle.net/10773/976.
Testo completoAbstract (sommario):
Doutoramento em BiologiaEspécies de Aeromonas encontram-se distribuídas por diferentes habitats, estando especialmente relacionadas com ambientes aquáticos. O seu papel em complicações na saúde humana e animal é reconhecido. De facto, não só pelo seu potencial de virulência, mas também pelos determinantes genéticos de resistência a antibióticos que possam conter, estes organismos constituem uma preocupação na medicina humana e veterinária. Assim, é essencial o estudo da diversidade de espécies de Aeromonas bem como explorar as suas características fenotípicas e genéticas que podem conduzir a impactos negativos. A água constitui um importante veículo de transmissão de microrganismos e espécies de Aeromonas estão amplamente distribuídas em águas tratadas e não tratadas. Em Portugal é ainda comum o consumo de águas não tratadas cuja qualidade, na maioria das vezes, não é sujeita a monitorização, como acontece por exemplo, em explorações agrícolas de gestão familiar. Neste estudo, investigou-se a presença de Aeromonas em águas não tratadas para consumo. Estabeleceu-se também uma linha horizontal de colheitas de diferentes amostras de origem agrícola com o intuito de avaliar a possibilidade de a água ser uma das vias de contaminação de culturas agrícolas e animais por espécies de Aeromonas. Obtiveram-se 483 isolados que foram discriminados por RAPD-PCR. 169 estirpes distintas foram identificadas ao nível da espécie por análise filogenética baseada no gene gyrB. Verificou-se uma frequente ocorrência bem como uma diversidade considerável de espécies de Aeromonas. Em alguns casos, as relações genotípicas entre isolados de diferentes amostras eram muito próximas. Adicionalmente, a maioria das amostras continha diferentes espécies e estirpes distintas da mesma espécie. A. media e A. hydrophila foram as espécies mais ocorrentes. Um grupo de isolados apresentou variantes moleculares de gyrB diferente das conhecidas até agora, o que indica que poderão constituir espécies não descritas. O perfil de susceptibilidade da colecção de Aeromonas a diferentes antibióticos foi estabelecido, constituindo um perfil típico do género, com algumas excepções. Estirpes multirresistentes foram encontradas. A presença de genes tet e bla foi investigada por estudos de PCR, hibridação e, em alguns casos, de sequenciação. Como era esperado, cphA/imiS foi o mais detectado. A detecção de integrões fez-se por PCR e hibridação e a sua caracterização foi feita por sequenciação de DNA; a sua ocorrência foi reduzida. A maioria das estirpes sintetizou enzimas extracelulares com actividade lipolítica e proteolítica que potencialmente contribuem para virulência. A análise por PCR e hibridação permitiram a detecção de vários determinantes genéticos que codificam moléculas possivelmente envolvidas em processos patogénicos. Diversas espécies de Aeromonas apresentando características relacionadas com resistência a antibióticos e potencialmente de virulência estão frequentemente presentes em produtos para consumo humano e animal em Portugal. ABSTRACT: Aeromonas spp. are present in a wide range of ecological niches, being mainly related to aquatic environments. Their role in human and animal health complications is recognised. In fact, not only for their putative virulence but also for the antibiotic resistance genetic determinants Aeromonas may harbour, these organisms constitute an issue of concern in human and veterinary medicine. Thus, it is essential to get knowledge on Aeromonas sp. diversity and on their genotypic and phenotypic characteristics that may lead to negative impacts. Water constitutes a good contamination route for microorganisms and Aeromonas are widespread in untreated and treated waters from different sources. In Portugal there is still an extensive use of untreated water which is not regularly monitored for quality. This is often the case in family smallholding farms. In this study untreated drinking and mineral waters were assessed for their content in Aeromonas spp. Furthermore, a sampling scheme was designed to investigate the occurrence and diversity of Aeromonas sp. in different agricultural correlated sources and to assess the possibility of water being the transmission vehicle between those sources. 483 isolates were obtained and discriminated by RAPD-PCR. Identification at the species level for 169 distinct strains was done by gyrB based phylogenetic analysis. Results demonstrated the frequent occurrence and considerable diversity of Aeromonas spp. In some cases, genotypic close relations were found between isolates from different sources. Also, most samples contained different species and distinct strains of the same species. A. media and A. hydrophila were the most occurring. A group of isolates displayed gyrB gene sequences distinct from the previously known, indicating that they may constitute representatives of non-described species. The antibiotic susceptibility profile of the aeromonads collection was established and constituted a typical profile of the genus, although few exceptions. Multiresistance patterns were found. The presence of tet and bla genes was investigated by PCR, hybridisation and, in some cases, sequencing analysis. As expected, cphA/imiS was the most detected. Integrons were screened by PCR and hybridisation and characterised by DNA sequencing; low occurrence was recorded. The bulk of strains was able to produce extracellular enzymes with lipolytic and proteolytic activities, which may contribute to virulence. PCR and hybridisation surveys allowed the detection of distinct genetic determinants coding for molecules putatively involved in pathogenic processes. Diverse Aeromonas sp. presenting distinct antibiotic resistance features and putative virulence traits are frequently present in many sources for human and animal consumption in Portugal.
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Bushula, Vuyiswa Sylvia. "Genetic diversity and pathogenicity of sorghum-associated Fusarium species". Diss., Kansas State University, 2017. http://hdl.handle.net/2097/35196.
Testo completoAbstract (sommario):
Doctor of PhilosophyDepartment of Plant Pathology
Christopher R. Little
Understanding the genetic structure of fungal pathogens enables the prediction of evolutionary forces that drive pathogen evolution, which assists informed decision-making regarding disease management. The genetic structure of Fusarium thapsinum and F. andiyazi, two important pathogens that cause grain mold and stalk rot of sorghum (Sorghum bicolor), are little understood. The genetic structure and pathogenicity of a F. thapsinum population from sorghum in Kansas were evaluated with amplified fragment length polymorphisms (AFLPs), vegetative compatibility groups (VCGs), sexual cross-fertility, and seedling pathogenicity. Two sympatric populations and a genetically intermediate "hybrid" group were identified in Kansas. Seedling pathogenicity of strains ranged from non-pathogenic to pathogenic, which may be partially attributable to genetic variability in the F. thapsinum populations. Genetic relatedness between populations of F. thapsinum from sorghum in Kansas, Australia, Thailand, and three African countries (Cameroon, Mali, and Uganda) were evaluated with AFLP markers and sexual crosses. Genetic diversity was high in all locations, but female fertility is very low. These results are consistent with the hypothesis that both sexual and asexual modes of reproduction are important components of the life cycle of F. thapsinum in these populations. More strains from Kansas and Africa were available for analysis than from Australia and Thailand, so the Kansas and Africa populations dominated the genetic structure observed. The two smaller populations from Australia and Thailand were more closely related to the Kansas population than they were to the African population. The three non-African populations contained information from the African population and from other, as yet unidentified, source population(s). Identifying the population(s) from which this genetic diversity originated is an important unanswered question. Stalk rot of sorghum was evaluated by inoculating stalk rot sensitive and stalk rot resistant sorghum lines with six genetically diverse F. thapsinum strains from Kansas under field and greenhouse conditions. One susceptible line (Tx7000) and two resistant lines (SC599 and BTx399) were evaluated in the field but only Tx7000 and SC599 were evaluated in the greenhouse. Disease severity was measured by major lesion length and the number of nodes crossed by the lesion. There were differences in aggressiveness amongst the F. thapsinum strains in both the greenhouse and field evaluations. This study provides the first evidence for differences in stalk rot aggressiveness amongst F. thapsinum strains and highlights the importance of challenging germplasm with well-characterized strains that represent the genetic spectrum of the entire population. The genetic diversity within F. andiyazi populations and some closely related strains was evaluated with AFLP markers. Phylogenetic and STRUCTURE analyses of the AFLP markers grouped the 81 F. andiyazi strains into three distinct clusters. The clusters were not based on the geographic origin of the strains. These results indicate the presence of at least one and possibly two undescribed sister taxa of F. andiyazi. More work is needed to further characterize these sister species of F. andiyazi and to understand their role in sorghum pathogenicity. There is genetic variation in global populations of F. thapsinum and the observed variation could be associated with variation in both seedling and adult plant pathogenicity. The study of F. andiyazi populations validated the need to properly identify and characterize Fusarium spp. associated with sorghum from different regions of the world.
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Cuschieri, Katie Sarah. "Species diversity of aggregate-associated marine ammonia-oxidising bacteria". Thesis, University of Aberdeen, 2000. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602054.
Testo completoAbstract (sommario):
Two broad communities can be distinguished in marine systems, those attached to amorphous aggregate material dispersed throughout the water column and those that are freely suspended in the water column (planktonic). It has been suggested that two distinct microbial populations are associated with each habitat due to phenotypic adaptation to the different conditions in aggregates and the surrounding water. The aim of this study was to investigate the diversity of aggregate-associated and planktonic marine ammonia oxidisers (AOBs - the organisms responsible for the rate limiting step in nitrification) in both natural environments and laboratory-reared systems and to determine whether aggregate material selected for particular groups of AOBs. Detection of AOBs relied heavily on the use of molecular analysis of extracted DNA. Thus, a preliminary study was performed to assess whether preferential lysis occurred when representatives of both genera within the B-subgroup AOBs {Nitrosospira multiformis and Nitrosomonas europaea) were exposed to lysis procedures commonly applied to marine samples. Minimal bias existed, with Nitrosomonas europaea proving to be less susceptible to lysis only when the lytic agents (sodium dodecyl sulphate and lysozyme) were absent or at concentrations 100-fold less than those applied in routine environmental extraction. Environmental populations of aggregate-associated and planktonic AOBs in the NW Mediterranean Sea were assessed in summer and winter at stations both within and beyond regions of fresh water inflow (the plume). Molecular analysis involved amplification, by the polymerase chain reaction, of 16S rRNA genes from extracted DNA using AOB-specific primers. Analysis of 16S rDNA sequences coupled with DGGE and specific probing revealed temporal and spatial effects in community structure of AOBs. In the summer, genus level selection of AOBs was observed with Nitrosospira dominating in the aggregate population and Nitrosomonas dominating in the planktonic phase. This was found in the surface waters of geographically distant sites within and outside the plume. Between-site differences were evident in the deeper waters with Nitrosospira-like sequences more abundant in plume diluted waters and Nitrosomonas like sequences more abundant outside this zone, while genus level selection between aggregate-associated and planktonic communities was not detected. In winter, a uniform pattern of AOB distribution emerged with an even distribution of two Nitrosospira sequences at each site on all aggregate and planktonic samples. The AOB community structure of sediment samples was not wholly resolved by application of direct molecular techniques and the culturable diversity was later examined by an enrichment-based approach. A laboratory-reared aggregate system was developed to assess the distribution and selection of inoculated pure and enrichment cultures of AOBs and to assess the effect of sampling technique on the observed community structure. Enclosed vessels containing North Sea water were rotated until aggregation of autochthonous particulate material formed discrete aggregates. No genus level selection of AOBs was observed in aggregate-associated and planktonic communities in North Sea water yet differences in the distribution of closely related sequences within cluster 1 Nitrosospira were observed between the two communities. Observed aggregate and planktonic community structure was affected by the method used to separate the two fractions. Active bacterial production was not necessary for aggregate formation if a pooled suspension of aggregates was sterilised and added to a medium of cell-free filtered sea water. Thus, the successful inoculation and retrieval of an N. multiformis culture within the cell free system suggested that it was appropriate for investigation of the colonisation dynamics of inoculated AOBs.
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Santos, Ricardo. "Diversity, stress responses and ecological behaviour of Mycobacterium species". Thesis, Queen's University Belfast, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709877.
Testo completoAbstract (sommario):
Mycobacterium is one of the oldest known bacterial genera and its species are commonly associated with human and animal disease, although most are free-living saprophytes which form part of a balanced microbial community in natural habitats such as water and soil Mycobacteria are highly distributed in the environment and in man-made water infrastructures mainly due to its robustness and ability to adapt Until now there are only scarce reports of their presence in extreme environments but no methodic and large-scale survey of these environments has been done in order to truly understand their distribution in such environments. This thesis encompasses the isolation of strains from 263 different positive samples and their identification using different techniques. The most commonly isolated species were Mycobacterium gordonae in Glacier National Park and Mycobacterium parascrofulaceum and Mycobacterium avium in Yellowstone National Park. Isolates were tested for their resistance co temperature, pH and different stressors, in an attempt to explain the remarkable resistance for most of the tested conditions, several cell characteristics were tested, including fatty acids composition, polyphosphate accumulation and catalase activity. Scanning Electron Microscopy was performed to have an insight into the genera! structure of the cells. Results emphasize the highly resilience of mycobacteria to different types of environmental stress. From the tested conditions, the subtle differences In the fatty add composition, in the catalase activity and polyphosphate accumulation, demonstrates that the formation of biofilm-like structures helps to understand cite highly resistance of the members of this genus.
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Barnes, Emma Catherine. "Chemical Diversity of Eremophila Species and Screening Library Generation". Thesis, Griffith University, 2012. http://hdl.handle.net/10072/366931.
Testo completoAbstract (sommario):
This thesis explores two aspects of natural product (NP) chemistry. In part A, the use of NPs as scaffolds in the generation of screening libraries was explored as a valuable way to produce structurally diverse compounds with lead- or drug-like physicochemical parameters. Part B describes the chemical investigations of several species from the under-studied Australian endemic plant genus Eremophila, which was selected for examination as it had high potential to be a source of both new chemistry and of unique scaffolds for screening library production.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Biomolecular and Physical Sciences
Science, Environment, Engineering and Technology
Full Text
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Estes, Becky Lynne Gjerstad Dean H. "Impact of interacting disturbances on longleaf pine communities". Auburn, Ala., 2006. http://repo.lib.auburn.edu/Send%206-15-07/ESTES_BECKY_24.pdf.
Testo completo
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Goodwin, Zoe A. "Completing the global inventory of plants : species discovery and diversity". Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:94f1a4d9-30fc-4f1b-8642-7b68760e1977.
Testo completoAbstract (sommario):
To complete an online world Flora by 2020 rapid progress is required towards understanding the taxonomy and distributions of the world's plants. This ambitious target set by the Global Strategy for Plant Conservation is hampered by two facts; first, many species of seed plant remain poorly known and second, the process of improving taxonomy and discovering species is not well understood. Here I investigate in detail the taxonomy and process of species discovery in a genus of tropical plants, Aframomum by examining specimens, taxonomic literature and authors of specimen determinations. I demonstrate that >50% of Aframomum specimens did not have the correct name prior to a recent comprehensive revision, that the number of specimens in herbaria doubled between 1970 and 2000, and that these results are also found in other taxa. I deconstruct the process of âspecies discovery' by identifying four key events: Initial collection, publication, conservation assessment, and distribution mapping. The time lags between the initial collection and completion of a) an accurate conservation assessment (101 years) and b) a comprehensive distribution map (115 years) demonstrate that many seed plant species published in the last 100 years are not fully understood. This is partly due to the fact that most species protologues (>90%) cite too few specimens at publication to produce an accurate conservation assessment. Furthermore, I explore variation in species' distribution patterns over time, taking account of specimen misidentification. Taken together the thesis identifies the lack of taxonomic capacity to efficiently deal with the tremendous influx of specimens since 1970, the poor current state of taxonomic knowledge of many taxa, and three significant time lags in the process of species discovery. Focused taxonomic effort is required for the successful completion of a world online Flora with conservation assessments to meet the 2020 GSPC target.
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De, Carvalho Ximenes Arimatéa. "Mangrove species range limits and species diversity: A macroecological approach from regional to global scales". Doctoral thesis, Universite Libre de Bruxelles, 2019. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/285690.
Testo completoAbstract (sommario):
The mangrove forest is an ecosystem distributed worldwide along tropical andsubtropical coastlines. The environmental conditions are known to affect species distributionpatterns, and to understand them is one of the main goals of biogeography. The association ofenvironmental factors (e.g. temperature and precipitation) and species distribution patterns haschallenged scientists since long. Species are distributed in a geographical space, however, whyspecies are present in a certain location but absent in another is a fundamental question inbiogeography. This PhD thesis aims at better understanding the most intriguing issues relatedto the role of environmental factors associated with mangrove distribution range limits andspecies richness from regional (Brazilian mangroves) to global scales.For the Brazilian mangroves, two scales were used to comprehend the spatial ecological nicheof mangrove tree species. First, the entire Brazilian mangrove-lined coast was considered, andseveral environmental variables were used to explain what is driving mangrove tree speciesdistribution. Second, a detailed analysis of daily Sea Surface Temperature (SST) data for theBrazilian mangrove forest at the southernmost mangrove range limit was done, and comparedwith a site beyond the range limit. The chilling events of SST data, also considering oceancurrents, show that Laguncularia racemosa is probably bounded by the southernmost Brazilianmangrove limit because of a dispersal constraint rather than by the frequency of chillingevents. However, the abundance of L. racemosa in Laguna at the Southern mangrove rangelimit, compared with only a few individuals of A. schaueriana, is probably associated with thechilling events of SST constituting a constraint to the latter species. This proves that mangroverange limits are not explained by a single causeThis PhD thesis also has the objective to evaluate the influence of upwelling intensity onthe distribution worldwide, which is its approach at a global scale. The sea surface temperature(SST) had been identified as one of the key drivers of global mangrove distribution, given thecoincidence of isotherms with mangrove global limits. However, other factors play a role in thevariability of SST. Cold waters from deep ocean layers rise to the surface (upwelling systems),which reduces SST values and can trigger aridity. Although previous research has confirmedthat mangrove distribution is driven by a variety of factors, this PhD thesis additionallydemonstrates a significant influence of upwelling intensity, and hence provides elements for abetter understanding of the factors driving mangrove expansion/retraction at a global scale. Inaddition, this work emphasizes climate and oceanographic processes influencing mangroverange limits. While contributing to a better understanding of some of the most intriguingquestions on the macroecology of mangrove, this PhD thesis also raises new questions thatshould be studied by future research.Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Bogardus, David C. "Comparison of tree species richness and species diversity in public landscapes of Broward County, Florida". [Gainesville, Fla.] : University of Florida, 2009. http://purl.fcla.edu/fcla/etd/UFE0024623.
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Peh, Kelvin Seh-Hwi. "The relationship between species diversity and ecosystem function in low- and high-diversity tropical African forests". Thesis, University of Leeds, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.511142.
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Lee, Jonathan Eric. "Partitioning β-diversity in species-area relationships: implications for biodiversity and conservation". Miami University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=miami1273172956.
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Van, der Vyver Marius Lodewyk. "Restoring the biodiversity of canopy species within degraded spekboom thicket". Thesis, Nelson Mandela Metropolitan University, 2011. http://hdl.handle.net/10948/1564.
Testo completoAbstract (sommario):
I investigated the return of plant canopy diversity to degraded spekboom thicket landscapes under restoration treatment. I attempted the reintroduction of five nursery propagated and naturally-occurring plant species in severely degraded Portulacaria afra Jacq. (spekboom) dominated thickets that have been subjected to a restoration method involving the planting of dense rows of P. afra truncheons for various time periods and also in degraded and intact thickets. I also planted nursery propagated P. afra cuttings. An average of 30 propagules of each species, were planted in each of the chosen areas in two distinct seasons that exhibited distinct rainfall peaks. Sixteen propagules of P. afra were also planted in each treatment only once. Propagules of the two thicket woody canopy species (S. longispina and P. capensis) showed a total survival of 1% and 9%, respectively. Survival of L. ferocissimum and R. obovatum was 19% and 70% and all propagules of P. afra survived. Analyses showed that survival is primarily tied to a species effect, with R. obovatum and P. afra showing significantly better survival than the other species. Within the other surviving few species a significant preference for overhanging canopy cover was observed. The results show little significance of restoration treatment for propagule survival, suggesting that a range of conditions is needed for the successful establishment of canopy species that likely involves a microclimate and suitable substrate created by canopy cover and litter fall, combined with an exceptional series of rainfall events. I found that the high costs involved with a biodiversity planting endeavour, and the low survival of propagules of thicket canopy plant species (P. afra excepted), renders the proposed biodiversity planting restoration protocol both ecologically and economically inefficient. Restoration success involves the autogenic regeneration of key species or functional groups within the degraded ecosystem. Heavily degraded spekboom-dominated thicket does not spontaneously regenerate its former canopy species composition and this state of affairs was interpreted in terms of a state-and-transition conceptual model. Floristic analyses of degraded, intact and a range of stands under restoration treatment for varying time periods at two locations in Sundays Spekboomveld revealed that the stands under restoration are progressively regenerating canopy species biodiversity with increasing restoration age, and that intact sites are still the most diverse. The high total carbon content (TCC) measured within the older restored stands Rhinosterhoek (241 t C ha-1 after 50 years at a depth of 50 cm) rivals that recorded for intact spekboom thickets, and the number of recruits found within older restored sites rivals intact sites sampled. 2 The changes recorded in the above- and belowground environments potentially identify P. afra as an ecosystem engineer within spekboom dominated thickets that facillitates the build-up of carbon above- and belowground and the accompanying changes in soil quality and the unique microclimate aboveground, which enables the hypothetical threshold of the degraded state to be transcended. This restoration methodology is accordingly considered efficient and autogenic canopy species return was found to be prominent after a period of 35-50 years of restoration treatment.
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Kaambo, Eveline. "Investigation of South African estuarine microbial species and genome diversity". Thesis, University of the Western Cape, 2006. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_8171_1186398717.
Testo completoAbstract (sommario):
A study of the microbial diversity in sediments of the Great Berg River estuary is carried out using modern molecular phylogenetic methods. The aim of this study was to determine the effect of (pollution by) the effluents of the fish industry on the composition of the microbial community in the sediments. The diversity in microbial groups of sediment samples that received wastewater from the local fishing industry was investigated by a PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) approach and compared to an unaffected site.
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Veldkornet, Dimitri Allastair. "Morphological variation and species diversity of South African Estuarine macrophytes". Thesis, Nelson Mandela Metropolitan University, 2012. http://hdl.handle.net/10948/d1013001.
Testo completoAbstract (sommario):
Studies on morphological variation are important as it can depict the relationship with environmental factors clearly and convey an understanding of the manner, mechanism and factors influencing plant adaptation and evolution. Although many studies have been conducted on South African salt marsh plant physiology and phytosociology there are at present very few morphological studies on estuarine plants. The aim of this study was to compare the morphological variation of estuarine macrophytes in three different estuary types in the warm temperate biogeographic zone of South Africa and to compare characters used in the taxonomic descriptions of species with those measured in the field. Permanently open estuaries investigated were Ngqusi (WC), Kowie (KW) and Swartkops (SW) estuaries. The Knysna Estuary (KN) was the estuarine bay investigated and the temporarily open/ closed estuaries (TOCEs) were the East Kleinemonde (EK) and Great Brak (GB) estuaries. Macrophytes were morphologically different across different estuary types. This suggests that there were different factors operating between these estuary types that would directly influence the morphology of species. The variation of plant height with different estuary types can be attributed to the fact that smaller salt marshes also have smaller habitat ranges compared to larger ones. The variation in morphological characteristics such as plant height can also be attributed to biogeographical range. Most morphological characteristics measured in the field fall within previously published ranges, and so these characters are useful in delimiting species. There were significant relationships between phenotypic variables and multivariate environmental variables. The most important of these variables were soil electrical conductivity, soil organic content and soil water content. Specifically, plant height increased with water content and decreased with salinity, flower stalk length had strong significant positive correlations with moisture content, organic content and pH while there were strong significant correlations with redox potential and electrical conductivity. Salt marshes are considered ideal for studying variation of species due to the explicit environmental gradients and plants occurring in salt marshes are halophytes that exhibit a range of morphological traits that allows for growth and reproduction under the stressful and extreme conditions. Considering recent climate change predictions and the consequent effects on South African estuaries this study provides significant information with regard to the response of species to a changing environment. The study was also aimed at updating the existing botanical database for South African estuaries in terms of species occurrence in South African estuaries, taxonomic name changes of existing species, new species, common names and habitats. Species diversity indices were also calculated for different estuaries, estuary types and biogeographic zones and diagnostic descriptions of the dominant salt marsh species were developed. The objective of this was that these data should provide baseline information for determining habitat richness and plant species diversity of South African estuaries which in turn should be used in determining priority estuaries for conservation and management. The identification key, developed using the DELTA software, would also aid researchers, managers and laymen in identifying salt marsh species. Results showed that the total number of macrophyte species, including intraspecific taxa and macroalgae, was 242 in 53 estuaries that were updated . There was an increase in the number of taxa recorded in the database primarily due to 1) research focus and full taxonomic surveys on larger estuaries and the big research projects has led to the identification of more species, 2) the addition of species that are not characteristically known as estuarine species, 3) the addition of 50 macroalgal taxa and 4) minor changes due to taxonomic revisions of species and the addition of newly described species. The Shannon diversity index showed that greater species diversity was found in the Berg (Groot) Estuary (4.220) and the Uilkraals Estuary (4.025). The cool temperate bioregion was the most diverse in the number of taxa (58) with the highest Shannon index (4.736). Permanently open estuaries were the most diverse in the number of unique taxa (56) with the highest Shannon index (4.867). Estuarine managers need to be aware of the species diversity in different estuarine types as well as the associated impacts on them. Conservation planning must therefore include species. Diagnostic features of INTKEY indicated that all 57 taxa were distinguishable from each other. Contrary to expectations plant height and not floral morphology was the best diagnostic characteristic. Ecological information such as the estuarine habitat, where different life forms occur, was important in delimiting species.
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Chan, Ivis Julieta. "Modelling spatial turnover patterns in tree species diversity for conservation". Thesis, Bournemouth University, 2015. http://eprints.bournemouth.ac.uk/24394/.
Testo completoAbstract (sommario):
The planet’s biodiversity is increasingly threatened by the effects of rapid environmental change. Biodiversity loss led by expanding anthropogenic activity, combined with the effects of changing climatic regimes, pose a threat to natural communities and the ecosystem services that they underpin. Understanding how communities of species vary across space and the factors that drive such variation is essential to predicting the impacts of human and climate-induced changes on biodiversity and ecosystem services. This knowledge can be used to plan conservation areas that effectively represent the underlying ecological processes that maintain biodiversity and ensure the provision of ecosystem services crucial to human wellbeing. Beta diversity has been variably defined since the concept was first introduced as a measure of variation in species assemblages. This has given rise to the development of different measures of beta diversity, and to varying conclusions regarding the variation of species composition across space. In this thesis, I aimed to investigate the spatial structuring of tree species turnover patterns (beta diversity) and the potential drivers of these patterns, within the highly environmentally heterogeneous Mesoamerican region. In addition, the effect of habitat loss on tree diversity up to the year 2000 was estimated, and the representativeness of the protected area system was assessed in an effort to highlight potential areas of conservation concern across the region. The efficacy of ecoregions in representing turnover patterns was also assessed. The spatial structuring of areas of low similarity (high beta diversity) was clustered in the north and south of the study region, as well as within the Central American mountainous regions. Areas of low similarity mostly fell within dry, pine-oak, and montane ecoregions. Moist forests were indicated as having high similarity. The congruence of the modelled pattern of beta diversity in trees with patterns of high beta diversity in other taxa provides insights into areas of potential conservation efforts. Habitat loss in the past decade was high in the southern areas of the isthmus indicating that countries like Nicaragua, Costa Rica, and Panama had lost high proportions of their original habitat and species. However, habitat loss was intensive throughout the region, and areas of high beta diversity were found to be among the least represented in the current protected areas system. Classification based on beta diversity broadly resembled the WWF ecoregional classification for the region. This suggests that models based on broad climatic variables can help elucidate beta diversity patterns at broad spatial scales, although conservation planning also requires robust information at finer scales.
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Richard, Monique. "Fern species diversity in relation to spatial scale and structure". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape10/PQDD_0002/MQ44258.pdf.
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Richard, Monique 1972. "Fern species diversity in relation to spatial scale and structure". Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=20850.
Testo completoAbstract (sommario):
Species with different requirements can coexist if the environment varies in space; we therefore expect a positive relationship between species diversity and environmental heterogeneity. In this thesis I examine the influence of environmental structure on patterns of fern diversity in one hectare of old-growth forest and compare these patterns to other surveys covering a broad range of scales. The nineteen species recorded in the hectare had non-random spatial distributions and differed in their soil preferences. Diversity was positively related to soil moisture and negatively related to soil fertility, but there was no relationship with environmental variance. The counteracting influence of dispersal may predominate over selection processes at the hectare scale. Both species-area curves and the decreasing correlation of species composition with distance had very similar slopes over quadrat sizes ranging from 1 x 1 m to 50 x 50 km, suggesting that some diversity patterns may be independent of scale.
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Darwell, Clive T. "Species composition and patterns of diversity in fig wasp communities". Thesis, University of Reading, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.590090.
Testo completoAbstract (sommario):
Here I use the wasps associated with figs (Ficus, Moraceae) to investigate a central theme of describing and understanding the composition and patterns of diversity among fig wasp communities, largely with respect to geography. Namely. in describing a community, what factors need to be considered, what methods need to be implemented, and what evolutionary and ecological processes can be identified as having shaped the observed patterns. An introductory chapter outlines a number of issues in ecology with particular focus on fig wasps. Chapter 2 investigates the efficacy and level of agreement between modern molecular techniques in assessing species boundaries in the pollinating wasps of the Australian fig species, Ficus rubiginosa. Varying methods are equivocal but the performance of the ITS2 barcoding gene proves efficient and effective. Chapter 3 draws on these species delimitation findings to assess the diversity among the complex parasitic wasp communities that exploit two Australian fig-pollinating wasp mutualisms (F. rubiginosa and F. obliqua). In this chapter I am also able to test ecological hypotheses about the processes driving the generation and maintenance of biodiversity. Molecular species delimitation techniques augment species richness estimates whilst some fig wasp diversity patterns are predictable by a combination of morphological, molecular taxonomy and abundance criteria. Chapter 4 revisits the pollinating wasps of F. rubiginosa and shows them displaying disparities in demographic histories and population genetics that may explain these cryptic species' co-existence. Chapter 5 increases in geographical scope and compares the composition of two intercontinental fig wasp communities in China and Australia that are associated with the same wide-ranging fig species, F. benjamina. Molecular comparisons show that these communities appear similar despite being entirely composed of different species, whilst molecular dating techniques suggest that these communities were separated during periodS of biogeographical range expansion by their fig hosts.
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Green, Jennifer. "Genetic diversity in annual weed species at different spatial scales". Thesis, University of Reading, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394431.
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Gillen, Susan Marie. "Links between species diversity of ammonia oxidising bacteria and pH". Thesis, University of Aberdeen, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275092.
Testo completoAbstract (sommario):
Our ability to analyse natural microbial populations has recently been revolutionised by the application of 16S rDNA-based techniques. These techniques have proven particularly appropriate for ammonia oxidising bacteria, which carry out the initial and rate-determining step in nitrification. The strong effect of pH on ammonia oxidisers has been well documented; growth in liquid batch culture rarely occurs at pH values below 6.5 but autotrophic nitrification can occur in acidic soils. This study aims to examine the effects of pH in ammonia oxidisers in soil and laboratory culture. We employ both molecular techniques and traditional physiological investigations to examine community dynamics of Nitrosospira strains of the ammonia oxidising bacteria, and the links between species diversity and functional diversity.
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Munyenyembe, Mutiyenkhu Paul. "Biological diversity of species in the leguminosae genus Dolichos L". Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332062.
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Day, Andrew. "Environmental bacteriophages infecting Dickeya and Serratia species : receptors and diversity". Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/290114.
Testo completoAbstract (sommario):
Phytopathogenic Dickeya species inflict large economic losses on a variety of crops. A lack of effective chemical control methods has generated interest in the use of bacteriophages (phages) as a novel tool for biocontrol. In the last decade, six phages have been isolated in Belgium and Poland using Dickeya solani as the host. Previous work in this laboratory has isolated ninety phages capable of infecting D. solani. The majority have been morphologically classified as members of the Ackermannviridae family. In agreement with findings in Salmonella and Klebsiella species, the capsule of D. solani is a likely receptor of Ackermannviridae family phages. Analysis of D. solani strains carrying reporter fusions suggested that the capsule genes are expressed in response to nutritional stress, however disruption of the capsular polysaccharide cluster did not significantly impact virulence. Experiments assessing capsular polysaccharide as a putative receptor for Ackermannviridae family phages in nosocomial pathogen Serratia produced inconclusive results. Phageresistance due to random transposon mutagenesis identified genes encoding transcription factors and regulators, but none directly linked to capsular polysaccharide production. Thirteen phages were capable of infecting a wider host range of Dickeya species. Morphological and genomic analysis showed that six were Podoviridae family members, whilst the other seven were Myoviridae family members. These are part of the recently defined 'hairy Myoviridae', characterised by a distinct morphology. Another member of this grouping was isolated during this study, but is more closely related to phages of Erwinia amylovora. A subset of the Ackermannviridae family phages were shown to be capable of facilitating transduction. This makes them unsuitable for use in the environment due to the risk of deleterious horizontal gene transfer. This is also true for the Myoviridae family members, but not for one of the Podoviridae family members. This phage could therefore be a promising candidate for therapeutic use.
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Alsayied, Nouf Ahmad Fakieh Alsayied. "Molecular diversity and relationships of saffron and wild crocus species". Thesis, University of Leicester, 2015. http://hdl.handle.net/2381/32189.
Testo completoAbstract (sommario):
Crocus sativus L., saffron Crocus, is a sterile triploid (2n=3x=24) species of unknown relationship to other diploid and polyploid species in the genus Crocus (Iridaceae). The species have large genomes (typically 3000Mbp 1C), much repetitive DNA, and show high morphological diversity within and between species, with no clear phylogenetic patterns below the level of section Crocus, series Crocus. I aimed to examine molecular diversity in C. sativus and related species by analysis of sequences and IRAPs (Inter Retroelement Amplified Polymorphisms). Repetitive DNA sequences and genomic DNA from various species were used for in situ hybridization, with chromosome morphology, to infer relationships and ancestry of saffron. The IRAP analysis, involving 63 primer combinations and 4745 polymorphic bands, revealed no polymorphism within 17 saffron accessions obtained from across the world from Kashmir through Iran to Spain. In contrast, high levels of polymorphism were identified between accessions of six wild Crocus series Crocus species, with further variation between the species. Analysis of 123 sequences of the ATP-synthase gene and 107 TC25 gene-SSR sequences from seven saffron accessions and eight wild species showed that the saffron accessions often carried three alleles, a result also found with clustering of published EST sequences. The analysis showed many alleles were shared by Crocus species and did enable a well-resolved phylogeny. Chromosome analysis grouped saffron chromosomes into 8 groups of 3, but one chromosome differed from the other two. It was concluded 1) Saffron crocus has minimal genotypic variation and the triploid hybrid species is most likely to have arisen only once; 2) Saffron is a allotriploid species, with the most likely ancestors being C. cartwrightianus and C. pallasii subsp. pallasii (or close relatives). The results may facilitate resynthesizing saffron with improved characteristics and show the need for conservation and collection of wild Crocus.
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Mól, Abel Perigolo. "How many species? Ecological drivers of cricket (Orthoptera: Grylloidea) diversity". Universidade Federal de Viçosa, 2012. http://locus.ufv.br/handle/123456789/3946.
Testo completoAbstract (sommario):
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No capítulo 1, este estudo investiga os determinantes da diversidade e abundância de grilos de serapilheira, e as possíveis interações com feições geomorfológicas. Ainda, nós propomos uma abordagem analítica que inclui amostragem local passiva como uma explicação necessária para a variação da diversidade e evidencia eventuais efeitos do ambiente nas relações diversidade-abundância. Concluímos que os processos biológicas regulando o número de espécies de grilos não são diretamente afetados por feição geomorfológica. A riqueza local é mais provavelmente limitada por processos amostrais do pool regional. No capítulo 2, avaliamos se a diversidade de gêneros de grilos sul-americanos pode ser empiricamente explicada por área de distribuição e tamanho corporal. Analisamos as espécies reportadas pela Orthoptera Species File para a região Neotropical e estimamos a área de distribuição e biomas interceptados para cada gênero. A diversidade aumenta com a área, mas o aumento é maior em áreas descontínuas. A diversidade aumenta com tamanho corporal e área tanto em áreas contínuas quanto em áreas descontínuas. A distribuição descontínua podem ou subestimar a distribuição verdadeira ou superestimar o escopo do gênero. O aumento da diversidade com tamanho corporal foi contrário às nossas expectativas. Isso pode ser resultado de efeito amostral, isto é, grilos maiores são mais facilmente amostrados e identificados. Concluímos que a distribuição de dados de grilos, embora incipiente, são relevantes para explicar diversidade de espécies entre gêneros. Os processos biológicos envolvidos nas relações empíricas merecem melhor investigação.
On chapter 1, this study investigates drivers of the diversity and abundance of litter crickets, and their possible interactions with the geomorphological feature. Moreover, we propose an analytical approach which includes local passive sampling as a necessary explanation for diversity variation and thus highlights eventual effective influence of environment on diversity and diversity-abundance relationship. It is concluded that the biological processes regulating number of species are not directly affected by the geomorphological feature. Local richness is most probable limited solely by a sampling process of the regional pool, and sample size is determined by factors affecting all species equally, in other words, affect the number of individuals. At Chapter 2, we aimed to evaluate if genus diversity of South-American crickets (Orthoptera: Grylloidea) may be empirically explained by distribution area and body size. We analyzed all species reported in the Orthoptera Species File with geographic distribution range reported for the Neotropics. We estimated reported distribution area, as well as intercepted biome area for each genus. Diversity increased with area, but this increase was higher and steeper in discontinuous than continuous areas. Diversity increased with body and area in both continuous and discontinuous distribution areas. Discontinuous distribution records may either underestimate actual distribution area, or overestimate the genus scope. The increase of diversity with body size was opposite to our expectations. This could result from sampling effect, where larger cricket species with smaller body size would be under-represented due to taxonomic issues. We conclude that cricket distribution data, although sparse and not-systematic, are relevant to explain species diversity among genera. The biological processes involved in the empirical relationships deserve further investigation.
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Emrick, Verl III. "Disturbance, Functional Diversity and Ecosystem Processes: Does Species Identity Matter?" Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/23211.
Testo completoAbstract (sommario):
The role of disturbance is widely recognized as a fundamental driver of ecological organization from individual species to entire landscapes. Anthropogenic disturbances from military training provide a unique opportunity to examine effects of disturbance on vegetation dynamics, physicochemical soil properties, and ecosystem processes. Additionally, plant functional diversity has been suggested as the key to ecosystem processes such as productivity and nutrient dynamics. I investigated how disturbance and functional composition both singly and in combination affect vegetation dynamics, soil physicochemical properties, and ecosystem processes. I conducted my research at Fort Pickett, Virginia, USA to take advantage of the spatially and temporally predictable disturbance regime. In order to investigate the effect of plant functional composition on ecosystem properties, I used functional groups comprised of species with similar physiology and effects on ecosystem processes (C4 grasses, C3 grasses, legumes, forbs, woody plants). My study showed that two distinct disturbances associated with military training, vehicle maneuvers, and fire; affect functional group abundance, within functional group richness, and total species richness. I found strong effects of vehicle maneuvers on soil physical properties including an increase in bulk density and reduction in soil porosity. Fire also influenced soil physical properties but more indirectly through the reduction of above ground litter inputs. Though many of the measured physicochemical soil properties at Fort Pickett exhibited statistically significant effects of disturbance, the strength of these relationships appears to be modulated by influences of previous land use. I found statistically significant (P < 0.05) effects of disturbance on chlorophyll fluorescence, and effect of functional composition on available soil N- NH4+. In addition, I detected a significant interactive effect of disturbance class and functional composition on soil CO2 flux. The interactive effects of disturbance and functional composition on soil CO2 flux demonstrated how the loss of functional diversity could lead to instability in ecosystem processes in disturbed ecosystems. In a dynamic ecosystem, I demonstrated that the abundance and diversity of plant functional groups was significantly influenced by disturbance. By experimentally altering the abundance and diversity of these functional groups in a disturbance-mediated ecosystem, I showed that functional groups and presumably species influence key ecosystem processes.Ph. D.
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Grobbelaar, Joha. "Taxonomy, phylogeny and species diversity in the Ophiostoma quercus complex". Diss., University of Pretoria, 2009. http://hdl.handle.net/2263/79241.
Testo completoAbstract (sommario):
Polymorphic sequence-characterised marker assays from a recent diversity study on the Ascomycete fungus Ophiostoma quercus from Africa showed that some isolates collected from hardwoods were genetically distinct from O. quercus. In the present study we compared these African isolates with authentic O. quercus isolates, including the neo-type of the species from oak in France, by evaluating morphological characters, growth in culture, mating compatibility, and DNA sequence data. The isolates from Africa exhibited substantial variability in culture and were morphologically similar to O. quercus. Phylogenetic analyses of the ITS, β-tubulin and Translation Elongation Factor 1-α gene regions confirmed that the African group represents a distinct species in the hardwood lineage of the O. piceae-complex, closely related to O. ulmi and O. himal-ulmi. Mating studies between O. quercus and the African isolates showed that isolates predominantly mated with those of their own group, although there were rare cases of fertile crosses between the groups. Isolates residing in the African lineage is described here as a new species, O. tsotsi sp. nov., and is characterized based on morphological characteristics, growth in culture and sequence comparisons.Dissertation (MSc)--University of Pretoria, 2009.
Genetics
MSc
Unrestricted
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Roth, McKenzie L. "Analysis of Bacterial Abundance and Species Diversity in Various Soils". Ashland University Honors Theses / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=auhonors1355166102.
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Osburn, Andrew Wesley. "Understanding Weed Species Diversity in Railroad Crossing Rights-of-way". The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1574641066802878.
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Honorio, Coronado Euridice Nora. "Phylogeography and phylogenetic diversity of Amazon tree species and communities". Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/4605/.
Testo completoAbstract (sommario):
The Amazon rain forest is the most diverse ecosystem on Earth, harbouring more than ten thousand tree species. In this project, I used ecological and molecular information to explore how ecological factors and historical events have determined the species distributions and population genetic structure of tree species and the phylogenetic diversity of tree communities in the Amazon rain forest. Chapter 2 indicates that seasonally dry vegetation in northern South America represents a barrier to migration for Ficus insipida (Moraceae) and other wet-adapted Amazonian tree species as they have different plastid haplotypes restricted to Mesoamerica and Amazonia. Conversely, the ability of some pioneer species to survive seasonal drought may explain the weakly differentiated phylogeographic structure within these species, with some haplotypes occurring on both sides of this barrier. Chapter 3 explores whether patterns of population genetic structure in five widespread western Amazonian tree species are consistent with historical explanations. My results show that the genetic patterns among species are not entirely congruent suggesting that tropical rain forest species respond differently to long-term geological and climatic changes. Despite this, some tentative generalisations emerge, notably high genetic diversity and a strong geographic structure for plastid sequences suggesting long-term population stability across western Amazonia, and recent population expansions in the south-western Amazon. Chapter 4 uses 283 floristic inventories from the RAINFOR plot network to explore patterns of phylogenetic diversity across Amazonia. This study reveals that the species-rich communities of central Amazonia are dominated by phylogenetic close relatives compared to the equally species-rich communities of the north-west that tend to contain more distantly related species. Across Amazonia, an east-west gradient of the abundance of early divergent angiosperm clades was found, with the greatest percentage of tree species of Magnoliids and Monocots in the west. As these early diverging clades are also characteristic of pre-montane habitats, these results suggest that migration events from cooler environments at different geological times has played an important role in the assemblage of the most phylogenetically diverse communities in Amazonia. The findings from these three chapters corroborate the notion that both ecological factors and historical events have been important in determining species distributions and the phylogenetic diversity of tropical tree communities in Amazonia. Regional differences in genetic structure among populations, and phylogenetic diversity among communities, should both be taken into account in forest conservation planning and management.
43
Weiser, Michael Dennis. "Latitudinal Patterns of New World Species Diversity and Range Size". Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/195130.
Testo completoAbstract (sommario):
The latitudinal gradient in species diversity is one of the best-documented patterns in biogeography. Explanations for the latitudinal gradient in species diversity (LGSD) ranging from null models to evolutionary and ecological hypotheses rely on relationships between range size and species richness. I test Rapoport's rule, where mean range size of tropical organism is predicted to be smaller than for temperate and boreal organisms, using New World woody plants. Geometric constraint models (GCMs) posit that barriers to dispersal, in the absence of ecological and evolutionary gradients can generate gradients in species diversity. I describe an analytic solution for the most common geometric constraint model and test expected and observed richness patterns for New World palms. I show that domain truncation will inevitably and spuriously increase the predictive power of GCMs while potentially decreasing the predictive power of other competitor variables. The LGSD is often considered a general pattern driven by general processes. Assuming that generality of pattern may reflect generality of process, I examine the LGSDs for New World mammal orders and families, testing for generality in two components of the LGSD, shape and peak. The overall LGSD is not a general pattern for across mammal orders and families and therefore it is unlikely that the LGSD is generated by a shared general mechanism or historical process.
44
Chowdhury, Tanmay. "Ethnobotany of Dakshin Dinajpur district with special reference to diversity and conservation of ocimum species". Thesis, University of North Bengal, 2017. http://ir.nbu.ac.in/hdl.handle.net/123456789/2571.
Testo completo
45
Persson, Malin. "Changes in species diversity among echinoderms in the sill area of Gullmarsfjorden : Effects on changes in species composition among echinoderms - ecosystem functions and possible changes". Thesis, Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-23672.
Testo completoAbstract (sommario):
Increasing attention has been given marine benthic macrofauna due to its importance in marine ecosystems and for its value as bioindicator of environmental changes. One of the most abundant groups among benthic macrofauna are echinoderms which often hold keystone positions in the ecosystems and have proven to be good bioindicators. The aim of this study was to inventory echinoderms and analyze whether species diversity has change over time in Gullmarsfjorden, a fjord with limited water exchange and hence highly sensitive to environmental fluctuations. Also, what may have caused any changes and what potential effects can it have on ecosystems in the fjord, and which species may be valuable as bioindicators. The results show that species diversity of echinoderms has decreased significantly since the early 1900s and the main reduction have occured among species living on/in soft or sandy bottoms. Many of the lost echinoderms species are essential bioturbators and thus important to marine ecosystems. However, Echinocyamus pennatifidum, a sea urchin which is a valuable bioturbator may have established in the fjord during the last century judging from this study. Species like Asterias rubens and Psammechinus miliaris, which are common in the fjord, have also proved to be valuable bioindicators for abiotic changes such as increased CO2-levels and pollution of heavy metals and PCB.
46
Verschuyl, Jacob Pieter. "Biodiversity potential in the Pacific and Inland Northwest the relative importance of forest structure and available energy in driving species diversity /". Diss., Montana State University, 2007. http://etd.lib.montana.edu/etd/2007/verschuyl/VerschuylJ0507.pdf.
Testo completo
47
Qasim, Amina. "Diversitet av mossor och lavar på åkerholmar i ett öppet och ett skogsdominerat landskap". Thesis, Stockholms universitet, Institutionen för naturgeografi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-121430.
Testo completoAbstract (sommario):
De ekologiskt betydelsefulla småbiotoperna blir allt färre i det moderna jordbruket på grund av intensifieringen av jordbrukslandskapet som resulterat i ett allt mer fragmenterat landskap. För att kunna ge småbiotoper, såsom åkerholmar, ett optimalt skydd behövs flera studier om organismerna på holmarna, deras diversitet och spridning. I denna undersökning studeras artrikedomen av mossor och lavar på busk- och trädbekädda samt öppna åkerholmar i ett öppet- och ett skogsdominerat landskap. Analysen av artrikedom i studien tyder på att de finns fler arter av mossor och lavar i det öppna landskapet i förhållande till det skogsdominerade landskapet samt på de åkerholmarna som saknade busk- och trädvegetation. Dessa miljöer består av torr och stenig mark och växer igen relativt långsamt, vilket är gynnsamt för vissa mossor och lavar. Det fanns ingen signifikant korrelation mellan diversitet och storleken på åkerholmarna eller mellan diversitet och holmarnas avstånd till skog. Antalet arter i ett habitat kan bero på regionala artpoolen samt antalet potentiella kolonisatörer men även lokala processer. Vidare är det viktigt att nämna att studien tyder på att diversitet av mossor och lavar påverkas av förhållandena på holmarna, såsom busk- och trädtäckningen. Detta i kombination med en variation inom dessa små biotoper kan skapa goda förutsättningar för ett landskap med hög diversitet.The ecologically important small remnant habitats are becoming fewer in modern agriculture due to the intensification of agricultural landscapes that have resulted in an increasingly fragmented landscape. In order to provide an ideal conservation framework for small habitats, such as midfield islets, several studies about the organisms on the islets, their diversity and distribution are needed. In this study I investigated the diversity of mosses and lichens on open midfield islets with and without shrubs and trees in an open and a forest-dominated landscape. The analysis of species diversity in the study suggests that, overall; there are more species of mosses and lichens in the open landscape in relation to the forest-dominated landscape, and on the opened islets lacking shrub and tree vegetation. These environments consist of dry and rocky soils and overgrow relatively slowly, which is favourable for mosses and lichens. There was no significant correlation between diversity and size of the midfield islets or their distance to forest. The number of species in a habitat may depend on regional species pool and the number of potential colonizers but also local processes. Furthermore, it is important to mention that the study suggests that the diversity of mosses and lichens is influenced by the conditions on the midfield islands, such as shrub and tree cover. These conditions, combined with a variation within these small habitats can create good conditions for a landscape with high diversity.
48
Yenni, Glenda Marie. "Self-limitation as an explanation for species' relative abundances and the long-term persistence of rare species". DigitalCommons@USU, 2013. https://digitalcommons.usu.edu/etd/1958.
Testo completoAbstract (sommario):
Much of ecological theory describes species interactions. These interactions often play an important theoretical role in facilitating coexistence. In particular, rarity in ecological communities, though often observed, provides a significant challenge to theoretical and empirical ecologists alike. I use a plant community model to simulate the effect of stronger negative frequency dependence on the long-term persistence of the rare species in a simulated community. This strong self-limitation produces long persistence times for the rare competitor, which otherwise succumb quickly to stochastic extinction. The results suggest that the mechanism causing species to be rare in this case is the same mechanism allowing those species to persist. To determine if ecological communities generally show the theoretical pattern, I estimate the strength of frequency-dependent population dynamics using species abundance data from 90 communities across a broad range of environments and taxonomic groups. In approximately half of the analyzed communities, rare species showed disproportionately strong negative frequency dependence. In particular, a pattern of increasing frequency dependence with decreasing relative abundance was seen in these communities, signaling the importance of this mechanism for rare species specifically. Insight into the special population dynamics of rare species will inform conservation efforts in response to climate change and other disturbance. Further difficulties in the detection of theoretical patterns in ecological data may be a result of the ecological currency used. Though ecologists typically use abundance data to test theories, energy use is another ecological currency that may be more relevant in some cases. In particular when detecting patterns that are a result of species interactions, the currency used should be the one in which those interactions actually operate. I compare the results of using abundance and energy use to detect two processes with well-defined expectations. The first is a description of population dynamics, the above described relationship between relative abundance and self-limitation. The second, compensatory dynamics, is a description of community-level dynamics. I find that the currency used alters the results, and thus the species-level implications. It does not, however, alter the overall pattern that would have theoretical implications. Results in both currencies support the pattern of strong self-limitation for persistent rare species.
49
Sutherland, Darin Lee. "Phylogeography and Ecology of New Zealand Freshwater Amphipoda (Paracalliope, Paraleptamphopus, and Phreatogammarus)". The University of Waikato, 2006. http://hdl.handle.net/10289/2650.
Testo completoAbstract (sommario):
ABSTRACT This thesis examines phylogenetic patterns in three New Zealand amphipod taxa in relation to current geographic distributions and historical climatic (e.g. glaciation, marine inundation) and geological (e.g. mountain building) events using DNA sequencing and distributional data. It also examines how recognition behaviour can be used to delineate potential species boundaries and to assess the role of sexual selection. The endemic genus Phreatogammarus has been found in only a limited number of sites and is not very abundant. An analysis of the genetic variation of two species within the genus using allozyme electrophoresis revealed high levels of genetic differentiation among populations but low levels within populations. This suggested that limited dispersal occurred among habitats with one population possibly representing a cryptic species. The endemic freshwater genus Paraleptamphopus is thought to contain a large number of undescribed species with a number of these existing in small waterbodies such as seepages. Examination of the phylogeographic patterns using both mtDNA (CO1) and nuclear DNA (28S) showed that a number of distinct genetic lineages exist, with CO1 revealing 21 haplotypes with genetic distance of over 20%. Using a molecular clock rate of 2.4%, most haplotypes diverged approximately 8-12 million years ago during the Miocene era, possibly as a result of greater land availability increasing habitat diversity or by allopatric speciation. Morphological and genetic differences were not congruent, with morphologically similar taxa appearing among highly genetically distinct lineages, and some morphologically distinct forms appearing within single lineages. The distribution and habitat variables of 419 sites were analysed to determine what was affecting the presence or absence of Paraleptamphopus. The presence of native vegetation in catchments had a positive affect on Paraleptamphopus distribution suggesting that large anthropogenic changes in catchment vegetation could have a negative effect on their abundance. I found smaller waterbodies to be more important than larger ones highlighting the need to study such sites as rare taxa may be ignored. A better understanding is needed on the role of small waterbodies in promoting overall species diversity in catchments. Examination of Paracalliope fluviatilis phylogenetic patterns using the mtDNA gene CO1 showed that a number of separate clades existed suggesting long term isolation and limited dispersal among catchments. Due to the large genetic divergences among some populations there was the possibility that cryptic species might exist. Species recognition experiments were conducted on seven populations to help determine whether cryptic species were present. For the three most genetically divergent crosses there was bias against inter-population pairings, suggesting that there were between two or three separate species. Using a combined field and laboratory approach, size assortative mating was examined in Paracalliope fluviatilis. The field study showed positive size assortative mating and that larger females carried more eggs, suggesting they were more fecund. A series of laboratory experiments examining four existing theories explaining the phenomenon found that none adequately explained positive size assortative mating in P. fluviatilis. I therefore presented two new explanations to explain size assortative mating: a combination of female resistance and size-related variation in a male's capacity to amplex larger females or a form of indirect intra-sexual competition.
50
Uimaniemi, L. (Leena). "Maintenance of genetic diversity in four taiga specialists". Doctoral thesis, University of Oulu, 2004. http://urn.fi/urn:isbn:9514274105.
Testo completoAbstract (sommario):
Abstract
Genetic diversity in three taiga specialists – the Siberian
tit (Parus cinctus), the Siberian jay
(Perisoreus infaustus) and the Siberian flying
squirrel (Pteromys volans) – was assessed by
comparing DNA sequence variation across the mitochondrial control region
and allele frequencies of microsatellites from samples collected from
Fennoscandia and Siberia. Population sizes of these species have
declined in association with fragmentation and loss of suitable forest
habitat due to modern forestry practices in Fennoscandia. The red
squirrel (Sciurus vulgaris) served as a reference
for the flying squirrel.
Genetic differentiation among species studied ranged from a
panmictic population in the Siberian tit to that of the strong
differentiation of populations
(θST = 53%) in the flying squirrel
in Finland. MtDNA and microsatellite data, together with assignment
studies, showed the Siberian jay population to be significantly
genetically structured and supported the existence of a metapopulation
like structuring in Fennoscandia. Division of genetic variation among
flying squirrel populations along the ancient shoreline of the Littorina
Lymnea Sea stage of the Baltic Sea (7000 BP) and two geographically
associated branches in the minimum spanning network supported a two-way
colonisation history for the species. The Finnish inland appears to have
been colonised from the east in association with the arrival of Norway
spruce. At the same time, Coastal Finland was colonised from the
south-east through the Karelian Isthmus. Gene flow of the species
appeared female biased and restricted. Species exhibiting more
restrictive dispersal characteristics and habitat requirements possessed
stronger population genetic structure than those with opposite
characteristics.
Growth or contractions in population size leave characteristic
signatures in mtDNA that can be studied by comparing different sequence
diversity estimates among populations. I applied this method to the
species studied. Significant differences in nucleotide diversities
indicated restrictions in gene flow among populations in all species
studied. Half of the Siberian jay populations gave a signal of
population size bottleneck.
All the species studied showed differences in their population
genetic structures across their entire distribution ranges consistent
with the multirefugia model, most likely to be attributable to
differences in their ecological characteristics and Pleistocene
histories.