375 research outputs found

    The Spatial and Temporal Ecology of Seed Dispersal by Gorillas in Lopé National Park, Gabon: Linking Patterns of Disperser Behavior and Recruitment in an Afrotropical Forest

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    Western lowland gorillas: Gorilla g. gorilla) consume large quantities of fruit and disperse a great number of seeds. The majority these seeds are dispersed intact and viable in the dung. Dung is often deposited around the rim of a night nest or at a nest-site. Gorillas often construct nests in areas that have a sparse canopy, flattening the ground vegetation. These locations can be beneficial to the growth and survival of the seed species they disperse. Thus, not only are gorillas effective in terms of depositing seeds great distances from parent plants, away from the highest seed rain densities, they are also effective in directing seeds to potentially beneficial microsites. The objective of this research was to develop an understanding of the spatial and temporal patterns in fruit availability, seed deposition, and adult plants, and to test whether these patterns relate to the ecology of seed dispersal by gorillas. Results suggest that gorilla foraging and nesting behavior in particular, impose both spatial and temporal limitations to the distribution of dispersed seeds. In addition, temporal variation in the gorilla diet and factors that affect defecation rates and locations promote variation in the combinations: composition and abundance) of the seed species dispersed to different microsites. The clustered distribution of nest-sites leads to clumped and spatially restricted seed deposition patterns. Recruitment in gorilla-dispersed seed species corresponds with the aggregated: clumped) distribution of nest-sites. Gorillas have a long-lasting effect on the spatial structure and floristic composition of the forests they inhabit, particularly in large-seeded species

    Analysis of meso- and microscale hydrometeorological fluxes in TERENO preAlpine using WRF-LES

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    A Large-Eddy Simulation (LES) using the Weather Research and Forecasting (WRF) model is set up in a computationally efficient way, directly driving the single domain with reanalysis data as boundary conditions. The simulation represents two real episodes over a well-known and real area. It is shown that the model successfully produces turbulent structures as they are known from idealized LES in literature and that the inertial subrange of the turbulence spectrum is appropriately resolved. The simulated wind field is evaluated with measurements taken during the ScaleX-campaigns by a triple Doppler Lidar setup that can measure all three wind components with a high temporal and vertical resolution throughout the atmospheric boundary layer. Model results sufficiently recreate the measured wind speed and direction as well as the development of daytime and nocturnal boundary layers. The coarse spatial and temporal resolution of the boundary conditions limits the accuracy of the model, shown by the representation of low-level jets. A katabatic flow reveals that the model successfully produces local weather phenomena that are not present in the boundary conditions and proves that the model output can be considered as a four-dimensional representation of the flow structures for a known area. This is not achievable with measurements. The implementation of realistic soil information (moisture and temperature) allows for a simulation of the sensible and latent heat fluxes. The advantage of the model over measurements here lies in the possibility to evaluate the turbulent fluxes at every location and height and the chance to evaluate the dependence of the fluxes on the soil properties below. The presented setup can be used to gather in-depth knowledge of the small-scale flow structures in a known area or to generalize soil-atmosphere interactions for large-area climate models.Die Dissertation beschreibt die Rechenzeit-effiziente Realisierung und Analyse einer large eddy simulation mit dem Weather Research and Forecasting Modell, bei der die meteorologischen Randbedingungen für die einzelne Domain direkt aus Reanalysedaten abgeleitet werden. Die Simulation erstreckt sich über zwei reale 48-Stunden lange Perioden in einem realen Gebiet. Das Modell produziert genau die turbulenten Strukturen, die aus idealisierten Simulationen aus der Literatur bekannt sind. Die inertial subrange ist deutlich zu erkennen. Messdaten von einem aus drei Doppler Lidar-Geräten bestehenden virtuellen Messturm, der die drei Windkomponenten in hoher zeitlicher und vertikaler Auflösung messen kann und während der ScaleX-Messkampagnen zum Einsatz kam, dienen zur Evaluierung des Modells. Gemessene Windgeschwindigkeiten und -richtungen werden im Modell gut abgebildet; die Grenzschichtentwicklung bei Tag und Nacht ist angemessen repräsentiert. Limitierungen zeigen sich in der Abbildung der gemessenen low-level jets, deren Genauigkeit durch die unzureichende räumliche und zeitliche Auflösung der Randbedingungen begrenzt ist. Am Beispiel eines katabatischen Kaltluftabflusses wird gezeigt, dass das Modell mikrometeorologische Phänomene erzeugt, die nicht aus den Randbedingungen stammen. Das bedeutet, dass die Modellergebnisse ein vierdimensionales Abbild der Strömungsverhältnisse in einem realen Gebiet darstellen. Mit Messungen ist das nicht erreichbar. Durch die Implementierung gemessener Bodenfeuchtigkeit und -temperatur in das Modell lassen sich realistische latente und sensible Wärmeströme berechnen. Im Modell können diese, im Gegensatz zu Messungen, an jedem Ort und in jeder Höhe bestimmt werden und die Abhängigkeit von der Bodenbeschaffenheit wird beschreibbar. Der gezeigte Modellansatz kann zur Untersuchung von kleinräumigen Strömungsmustern oder zur besseren Beschreibung kleinskaliger Effekte von Boden-Atmosphäre Wechselwirkungen in gröber aufgelösten Modellen verwendet werden

    Self-Evaluation Applied Mathematics 2003-2008 University of Twente

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    This report contains the self-study for the research assessment of the Department of Applied Mathematics (AM) of the Faculty of Electrical Engineering, Mathematics and Computer Science (EEMCS) at the University of Twente (UT). The report provides the information for the Research Assessment Committee for Applied Mathematics, dealing with mathematical sciences at the three universities of technology in the Netherlands. It describes the state of affairs pertaining to the period 1 January 2003 to 31 December 2008

    The study of influence factors in x-ray computed tomography using simulation approach.

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    XCT simulation scanning was used throughout the study because simulation scanning has the flexibility in changing scanning parameters as well as improving the efficiency. The research investigated the effect of voltage, scattering-contamination and multi-sampling on the quality of 2D image projection. For The study tested factors of scattering-contamination, multi-sampling and cone-beam angle on dimensional measurement error with the numerical geometry samples including spheres, cubes, cylinders and tubes. For cylinders and tubes, the measurement of outer diameter leaded more deviation than inner diameter. Scattering contamination had limited influencing (up to 1/35 of the voxel size) to the measurement result but scattering contamination can amplify the operator factor in the geometry determination step. 3X3 multi-sampling detector could optimise the measurement result when measuring the diameter of the cylinder. On the other hand, the effectiveness of the application of multi-sampling is related to the geometry features for measure, and the effect is independent to the scattering-contamination. When measuring circles on the tube, the cone-beam angle had only slight influence (up to 1/131 of voxel size) on the measurement error.PhD in Manufacturin

    The Utility of Fine-Scale Remote Sensing Data for Modeling Habitat Characteristics and Breeding Bird Species Distributions in an Appalachian Mature Deciduous Forest.

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    In this study, I tested the potential for remote sensing data with a high spatial resolution to model breeding forest bird species and their habitat at a fine spatial scale. The research took place on ridgetops in a large, relatively contiguous Appalachian mature deciduous forest in northwestern WV, USA. The remote sensing data sources were a leaf-on QuickBird satellite image (0.6-m panchromatic and 2.4-m multispectral) and a 3-m digital elevation model (DEM). For the first part of the study, I extracted spectral and textural measures from the satellite image and terrain information from the DEM. I then used these data to analyze avian community survey and habitat data collected at circular plots (n = 68) distributed across the ridgetops. The primary results of this analysis indicated that the satellite image provided information about trends in forest composition and structure across the study site, and further that a relatively simple plot-level measure of image texture (the panchromatic pixel standard deviation calculated at plot radii of 50 and 100 m) was a useful proxy of environmental heterogeneity for predicting the distributions of certain forest canopy gap-dependent bird species. For the second part of the study, I analyzed the habitat and remote sensing data at a finer spatial scale to develop remote sensing-based indices of forest structure and composition. These indices provided further insight into local variation in forest characteristics (e.g., in relation to topographic aspect) on the ridgetops. I also tested these indices, the DEM, and anthropogenic forest edge for modeling the breeding territory distributions of three focal species (Cerulean Warbler, Setophaga cerulea; Hooded Warbler, S. citrina; and Ovenbird, Seiurus aurocapilla) mapped over ~11 km of ridgetop transects. These models indicated the importance of local influences of terrain (e.g., east-facing aspects for Cerulean and Hooded Warbler, west-facing aspects for Ovenbird, and knolls for Cerulean Warbler), and forest edges (positive for Cerulean Warbler and negative for Ovenbird) on their distributions. Among the remotely-sensed indices, the index of forest structural complexity was primarily useful as a strong predictor of the distribution of the canopy gap-dependent Hooded Warbler. For the third and final part of the study, I used the locations of singing males of the three focal species collected across a greater extent of the site (~28 km of ridgetop transects) in point pattern analyses that incorporated the remote sensing data and the potential for intraspecific interactions (attraction and repulsion) between neighboring individuals. The results of these analyses supported that intraspecific interactions in addition to environmental influences as indicated by the remote sensing data explained the species’ fine-scale distribution patterns. While the individuals of all three species exhibited regular spacing over short distances that was consistent with competition for territorial space, Cerulean Warbler individuals exhibited more clustering than could be statistically accounted for by the remote sensing data, suggesting the importance of conspecific attraction in its distribution. In summary, my findings supported the potential application of fine-scale remote sensing data for purposes such as complementing coarse-scale environmental data (e.g., land cover maps) in predicting forest breeding bird species distributions, and for comparative analyses of the local spatial distributions of these species. The capacity for remote sensing data to provide useful environmental information at a fine spatial scale is likely to improve as the technology continues to develop
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