No description available.

No description available.

The Ediacara Biota is a distinct group of soft-bodied organisms that flourished in late Precambrian (Ediacaran) oceans. The succession at Mistaken Point, Newfoundland, contains the most extensive collection of Ediacaran fronds in the world, with hundreds of complete specimens spanning at least 10 million years. The goals of the completed thesis were to investigate the growth strategies, preservational biases, function, and taxonomy of Ediacaran fronds through the use of qualitative morphological descriptions and quantitative morphometrics. Several of these mathematical techniques had not been previously applied to the Ediacara Biota, and strengthen traditional descriptive techniques through mathematical scrutiny. The second chapter applies standard biometric and principal components analyses to the cosmopolitan frond Charniodiscus from Newfoundland, which allowed for rigorous definition of two new closely related species that evolved differently shaped petalodiums to extract nutrients from different levels in the water column. The third chapter utilizes "landmark morphometrics" to interpret the original 3D shape of Charnia. These techniques suggest that traditional descriptions of Ediacaran fronds as sheet-like organisms are incorrect, and are a direct result of preservational processes. It was demonstrated that branch rigidity is species specific, resulting in the description of a new species of ancestral Charnia. The fourth chapter describes a new species of multifoliate rangeomorph frond that was preserved in four unique taphonomic settings. Only through comparison of specimens from all four preservational regimes was it possible to reconstruct the original morphology of this frond, and isolate taphonomically based features from true morphological characters. The final chapter reviews the biological significance of the frond morphoshape, and proposes that the present emphasis on overall shape in Ediacaran taxonomy is inherently flawed. It is recommended that a new system be erected to classify Ediacaran fronds based on branching architecture, as frond morphology most likely represents a common need to extract nutrients from the water column, and therefore represents a shared ecology, not ancestry. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2007-10-09 15:06:08.885

No description available.

Zugl.: Hamburg, University, Diss., 2008.

Zugl.: Hamburg, University, Diss., 2008.

A Thesis Submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in Fulfillment of the Requirements for the Degree of Doctor of Philosophy. October, 1995. / The methods of vicariance biogeography are in general rendered equivocal by widespread taxa. Standard methods resort to ad hoc assumptions in their treatment of widespread cases, and the results are always si bordinate to the addition of new data on endemic sister taxa. I introduce an alternative method for the analysis of widespread taxa based on the vicariance model. The method requires first the development of a habitat model for each species included in the analysis. I analyse the actual and "potential" distributions by cladistic methods, employing a weighting system designed to factor out the influence of ecological similarity. The resolution of the inferred area relationships is seen to increases with the application of the weighting-compelling evidence that the pattern reflects historical relationship. I review current approaches to the modelling of habitats. All seem to be based on an ecological model of equilibrium, where the limits of actual species distributions are thought to reflect habitat, as if historical contingency played no significant part in determining the shape of real distributions. Under this model all approaches are group discrimination methods. I reject these methods and develop a new method based on principal component analysis. I analyse the distributions of all extant endemic African antelope and derive probability surfaces for each species. The model output can be interpreted as species distribution free oflHstory-its potential distribution. This is different from assuming that actual distributions are free of history. Areas oferdemism are seen to be historical entities, not simply distributional ones, and the resulting area cladograrn is interpreted as the hierarchical pattern of endemism. A striking feature of the inferred pattern of endemism is the intersection of an east-west equatorial biota, and a north-south savanna biota. These bisect in East Africa at the centre of highest antelope diversity. I predict that this feature will be seen to be the most persistent feature of endemic structuring in other African taxa with high East African diversity. / AC2017

No description available.

No description available.

En los diferentes ecosistemas de la Amazonía peruana, las raíces de la gran mayoría de plantas forman una simbiosis de tipo mutualista con hongos de micorriza arbuscular (HMA). Se conoce que estos hongos constituyen un componente clave para el funcionamiento eficiente de los bosques, principalmente por dar a las plantas una mayor capacidad para absorber fósforo y agua del suelo, ayudar en la agregación de las partículas del suelo dándole mayor estabilidad y contribuir con el almacenamiento de carbono en el suelo a través de la producción de glomalina.Por otro lado, en la Amazonía del Perú existen siete tipos de suelos dominantes, de los cuales los Ultisoles ocupan aproximadamente el 65% del total, equivalentes a 49,7 millones de hectáreas, que se caracterizan por ser deficientes en fósforo. En estudios realizados en bosques en las localidades de Yurimaguas y Pucallpa, donde prevalece este tipo de suelos, se ha encontrado la presencia de HMA, asociados con la mayoría de especies vegetales nativas, lo que indica su importancia para el crecimiento y desarrollo de estas. Sin embargo, cuando se evalúan las pérdidas de la biodiversidad causadas principalmente por la deforestación se toman solo en cuenta a las especies de flora y de fauna y no se considera a la biota del suelo, incluyendo a los HMA, como si esta no tuviera relevancia en el funcionamiento de los bosques. Por otro lado, la distribución geográfica de las poblaciones de HMA es muy variable, tal como se ha descubierto en los estudios realizados que corroboran descubrimientos hechos en la Amazonía de Colombia y Brasil, de que la biota que podría estar perdiéndose por prácticas poco conservadoras de manejo y explotación. Se discuten las posibles causas de estos hallazgos y los efectos de la deforestación en las poblaciones de estos hongos y se presenta a la investigación en cuanto a la distribución geográfica de los HMA como una prioridad en la Amazonía peruana, especialmente dirigida a su utilización en programas de reforestación y recuperación de áreas degradadas con especies nativas en las diferentes áreas deforestadas de la Amazonía