• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1313
  • 744
  • 298
  • 99
  • 69
  • 40
  • 35
  • 32
  • 27
  • 17
  • 16
  • 11
  • 11
  • 11
  • 11
  • Tagged with
  • 3180
  • 951
  • 709
  • 671
  • 578
  • 474
  • 378
  • 354
  • 342
  • 325
  • 303
  • 251
  • 249
  • 218
  • 204
  • 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.
91

The molecular systematics of Ulva Linnaeus and Enteromorpha Link (Ulvales, Chlorophyta) from the South Western Cape, South Africa

Kandjengo, Lineekela January 2002 (has links)
Bibliography : leaves 64-79. / Both Ulva and Enteromorpha are very common, ubiquitous, and environmentally important genera of green seaweeds. The evolutionary history of Ulva species is poorly understood, stemming from a lack of diagnostic, non-molecular systematic characters. This study addresses the following questions: i) Do the two genera represent distinct entitiesj ii) What are the relationships among local putative species; iii) Do the recognized species represent monophyletic lineages; iv) How closely are local species related to those from elsewhere? These questions are addressed using nuclear ribosomal DNA ITS sequences from 48 local samples plus data on 16 samples from GenBank.
92

Studies in the Dryopteris inaequalis (Dryopteridaceae) complex

Kwembeya, Ezekeil Gwinyai January 2000 (has links)
Bibliography: leaves 58-64. / The taxonomy of Dryopteris inaequalis complex is reviewed. The use of a large sample size permitted quantification of variation within and among groups. Phenetic methods in this study revealed the existence of six groups, five formerly described taxa and one new taxon, D. pseudopentheri sp. ined. The new species is defined on both macromorphological grounds. Dryopteris lewelleana Pic.Serm. and d. inaequalis (Schltdl.) Kuntze var. atropaleacae Schelpe are placed in synonymy under D.fadenii Pic.Serm. and D.inaequalis respectively. The phylogeny of the complex is reconstructed using cladistic analysis of morphological characters. Dryopteris manniana (Hook.) C.Chr., the probabl sister species is used as an outgroup for the analysis. Phylogenetic analysis revealed that there are four monphyletic species and two metataxa in the complex. Evidence from Scanning Electron Microscopy, micromorphology, macromorphology and cytology is used as a basis for classification. Trichome characters, indusium, spore and guard-cell sizes proved to be of great taxonomic utility in defining species and cytotypes in the complex. Guard-cell and spore sizes in the different taxa are positively correlated to ploidal level. Illustrations of some microcharacters are provided. The taxonomic treatment includes a key, descriptions of the species based on the characters studied and a distribution map.
93

Phylogenetic relationships of the African species of the genus Merxmuellera Conert (Poaceae: Danthonioideae)

Mafa, Paseka January 2001 (has links)
Bibliography: leaves 89-101. / This study expands on existing molecular (rpoC2 and ITS) and morphological data sets to further test the hypothesis of non-monophyly of Merxmuellera sensu lato. The results reveal that despite high levels of resolution, the morphological data yield poorly supported phylogenies due to high levels of homoplasy in the dataset.
94

Assessing Environmental Stress on the Loggerhead Sea Turtle (Caretta caretta) in Virginia Waters

Bellmund, Sarah A. 01 January 1988 (has links)
No description available.
95

Taxonomy and phylogeny of red-tailed francolins (Genus Peliperdix)

Nangammbi, Tshifhiwa Constance January 2003 (has links)
Bibliography: leaves 25-31. / The Red-tailed Group of francolins falls within the class Aves, order Galliformes, family Phasianidae and genus Peliperdix. These are small francolins consisting of three putative species (Peliperdix coqui, P. albogularis and P. schlegelii) that are largely allopatric. Two species (P. coqui and P. albogularis) are considered to be polytypic species, but is a large discrepancy in the number of subspecies attributed to P. coqui and P. albogularis. The mitochondrial cytochrome b gene, organismal characters and combined data were used to identify diagnosable taxa, test the monophyly and reconstruct the phylogeny of the Red-tailed Group. Sixteen exemplars of the Red-tailed Group (representing all species and nearly all subspecies currently recognised in the genus Peliperdix) from different geographical localities were studied. Maximum likelihood (cyt b), maximum parsimony (cyt b, organismal, combined) , distance analysis (cyt b) were performed to resolve the phylogenetic relationships among them. The trees obtained from DNA sequence, organismal and combined data were incongruent in respect to the position of some taxa. The monophyly of the Red-tailed Group seems to be well supported, but the identity of, and interrelationships between the subspecies and species are less well resolved. The morphological and combined tree probably reflects the taxon phylogeny better than the tree based on mitochondrial DNA. only. The most remarkable result that is strongly supported by both organismal and combined trees was that they bring clear resolution between P. albogularis and P. schlegelii as two separate species from P. coqui. Due to the short number of DNA sequences obtained, one cannot make a decision as to whether the subspecies should be elevated to species. Finally, it is suggested that more systematic studies must be done based on multiple independent data sets in order to obtain a robust taxonomy and phylogeny for this group.
96

Taxonomy, phylogenetic and biogeographical relationships of African grassland Francolins (Genus: Scleroptila)

Mandiwana, Tshifhiwa G January 2003 (has links)
Bibliography: leaves 23-28. / The potential for using a combination of molecular and whole-organismal data has opened up new avenues for avian taxonomy, phylogenetics and biogeography. Such a multifaceted approach is used here to identify diagnosable taxa within the Orange River Francolin Scleroptila levaillanloides species complex and resolve evolutionary relationships between these taxa and other mono-and polytypic forms within the Red-winged Group of francolins (= genus Scleroplila sensli lalo). Mitochondrial cytochrome-b DNA sequence data (±250 b.p.) from 50 individuals and 19 morphological characters extracted from reports in published literature were employed to achieve these aims. These characters were analysed separately and also in combination using maximum parsimony (DNA sequences and organismal data), maximum likelihood (DNA sequences) and distance (DNA sequences) analyses. Monophyly of the Red-winged Group plus the Ring-necked Francolin Dendroperdix slreptophorus was supported by all the analyses (bootstrap support ranged from 50%-94%) except distance analysis. The Orange River Francolin complex was found to be non-monophyletic. Two distinct clades were identified, one comprising taxa from southwestern and the other from northeastern Africa. Morphological analysis yielded a distinct clade of the southwestern Orange River Francolin. The other polytypic species and assemblages thereof show poor resolution. The results of this study clearly demonstrate a need for further assessment of the taxonomic status of Scleroptila spp. and their phylogenetic relationships.
97

Further studies with Melianthus L. : a molecular phylogeny, evolutionary patterns of diversification in the genus and pollinator syndromes

Henning, Jack January 2003 (has links)
Bibliography: leaves 84-100. / A phylogeny was produced for the eight taxa comprising the largely South African genus Melianthus L. based on two plastid markers (trnL-F and psbA-trnH) and one nuclear marker (ITS). Topological comparisons with a tree based on an existing morphological data set revealed significant incongruence leading to a loss of resolution upon combination. Ultimately, the combined three-gene data tree was selected as the strongest phylogenetic estimate for Melianthus based on its better resolution and greater support levels. This tree confirms the monophyly of Melianthus with M. major being resolved as sister to the remainder of the genus. Within the remaining clade, M. villosus is resolved sister to a clade comprising two morphologically distinct subclades, one of these being noted for a western distribution (comprising M. elongatus and the M. pectinatus complex), the other being centred farther east (comprising M. cocomosus and the M dregeanus complex). A molecular clock analysis was employed to date the emergence of specific taxa and clades, while ancestral range and habitat reconstructions were performed to determine historical conditions under which these groups and their morphological novelties arose. A scenario depicting the evolution and diversification of Melianthus is developed against a backdrop of the paleo-history of southern Africa. The genus appears to have originated in the eastern part of South Africa during a mild, mesic Oligocene with subsequent westward expansion into drier habitats of Miocene and Pliocene origins. Observations of bird visitors to a range of Melianthus species indicate that the genus employs a generalist pollination syndrome, thus refuting suggestions of a co-exclusive relationship with sunbirds (Nectariniidae). Nevertheless, the genus is undeniably ornithophilous. Nectar studies reveal interspecific variation in both the volume and concentration of nectar produced as well as in nectar colourition.
98

Phylogenetic studies in the genus Jamesbrittenia tribe Manuleae, family Scrophulariaceae

Herron, Margaret January 2006 (has links)
Word processed copy. / Includes bibliographical references. / Jamesbrittenia is a genus of 84 largely perennial sub-shrubs and herbs with a wide distribution in southern Africa (except J. dissecta in Sudan, Egypt and India). Plastid (rps16 and psbA-trnH) and nuclear (GScp) sequences were obtained for 42 species, mostly from the arid winter-rainfall west and southern regions of southern Africa. Applying both parsimony and Bayesian inference to combined molecular and morphological data sets, a phylogenetic hypothesis which is robust at the deeper nodes, was produced. This supports the monophyly of Jamesbrittenia, and also indicates the early divergence of J. ramosissima and three major clades.
99

Bird Conservation Value of Golf Courses

LeClerc, Joshua Elliott 01 January 2004 (has links)
No description available.
100

Reducing Avian Collisions With Human-Made Structures: A Sensory Ecology Approach To Open-Air Settings

Boycott, Timothy James 01 January 2020 (has links)
Billions of birds fatally collide with human-made structures each year. These mortalities have impacts on species of conservation concern and potentially on avian populations as a whole. This source of human-wildlife conflict also places economic and operational constraints on various human industries. Furthermore, with continued increases in urbanization, the rate and extent of collisions continues to increase. Efforts to reduce collisions have largely centered on making structures more visible to birds but have been met with limited success. Currently, there is a call for solutions to be tailored to both the environmental context of hazardous structures and to the sensory ecology of at-risk birds. In Chapter 1, we review how and why sensory ecology will help reduce in-flight collision risk for birds. A growing understanding of the sensory systems of birds and of the interface between these systems and the environment will enable the design of appropriate warning and deterrent signals. In particular, we review avian auditory and visual sensory ecology to better understand the susceptibility of birds to collisions and to recommend effective signal design. We highlight the ubiquity and salience of multi-modal signals in avian ecology and evolution, particularly as warning signals, and propose the use of multi-modal signals in mitigating collisions. We encourage the use of animal behavior frameworks to assess collision risk and collision mitigation approaches. Behavioral analyses offer numerous advantages over traditional collision measures, such as mortality estimates. Behavioral data can be generated quickly, render large sample sizes, and allow more nuanced perspectives of the context-dependence of collisions. In Chapter 2, we investigate the use of acoustic signals to reduce avian collisions with structures in open airspace. Birds have largely evolved without tall human-made structures in their flight paths and, consequently, avian perception and behavior may not be suitably primed to detect these novel hazards. Our previous work in captive settings showed that acoustic signals aid in drawing the attention of flying birds to potential collision hazards, influencing flight behavior. The current work corroborates these findings in a field setting. We projected acoustic signals into open airspace surrounding communication towers and quantified movement patterns of birds, to indicate potential collision avoidance behavior. Our results show a ~15% reduction in overall bird activity surrounding towers during sound treatment conditions, compared with control trials. Furthermore, flight movement patterns during sound treatments were characterized by significantly greater distances from and greater displacement of travel direction relative to towers, compared with control trials. Flights during sound treatments also showed significantly slower velocities, compared with control trials. Lower frequency sound stimuli (4-6 kHz) produced larger effect sizes than higher frequency stimuli (6-8 kHz). Results also co-varied with tower location and data collection date, reinforcing an appreciation of the context-dependent nature of collision risk. Our findings will inform the field of avian sensory ecology and help to assess the use of acoustic signals in collision mitigation measures.

Page generated in 0.0816 seconds