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Several Kilometres (several + kilometre)

Distribution by Scientific Domains

Earth and Environmental Science	60%
Life Sciences	40%

Selected Abstracts

An economic model of the limits to foraging range in central place foragers with numerical solutions for bumblebees

ECOLOGICAL ENTOMOLOGY, Issue 3 2000
James E. Cresswell
Summary 1. A model is described that evaluates the maximum economic foraging range in central place foragers by using optimality criteria to discriminate between foraging sites at different distances from the forager's central place. 2. The basic model can be varied to suit foragers that optimise either their rate of net energy uptake or their foraging efficiency. 3. The model requires specification of the time and energy budgets of travel and foraging, and of the rewards obtainable at potential foraging sites. 4. The specific case of bumblebees, whose foraging ranges are poorly known, is considered. 5. Numerical solutions of the model for parameter values that represent bumblebees and their forage predict economic foraging ranges exceeding several kilometres. The model demonstrates that economics alone can explain extensive flight ranges in bees. [source]

Lithology and fluid prediction from amplitude versus offset (AVO) seismic data

GEOFLUIDS (ELECTRONIC), Issue 4 2003
D. J. Davies
Abstract Seismic reflection data as used in the oil industry is acquired and processed as multitrace data with source-receiver offsets from a few hundred metres (short offset) to several kilometres (long offset). This set of data is referred to as ,pre-stack'. The traces are processed by velocity analysis, migration and stacking to yield a data volume of traces with ,zero-offset'. The signal-to-noise enhancement resulting from this approach is very significant. However, reflection amplitude changes in the pre-stack domain may also be analysed to yield enhanced rock physics parameter estimates. Pre-stack seismic data is widely used to predict lithology, reservoir quality and fluid distribution in exploration and production studies. Amplitude versus offset (AVO) data, especially anomalous signals, have been used for decades as indicators of hydrocarbon saturation and favourable reservoir development. Recently, enhanced quantification of these types of measurement, using seismic inversion techniques in the pre-stack domain, have significantly enhanced the utility of such measurements. Using these techniques, for example, probability of the occurrence of hydrocarbons throughout the seismic data can be estimated, and as a consequence the many pre-stack volumes acquired in a three-dimensional (3D) can be survey, reduced to a single, more interpretable volume. The possibilities of 4D time lapse observation extend the measurements to changes in fluid content (and pressure) with time, and with obvious benefits in establishing the accuracy of dynamic reservoir models and improvements in field development planning. As an illustration, recent results from the Nelson Field (UK North Sea), are presented where we show the method by which probability volumes for oil sands may be calculated. The oil,sand probability volumes for three 3D seismic datasets acquired in 1990, 1997 and 2000 are compared and production effects in these data are demonstrated. [source]

Thresholds in landscape connectivity and mortality risks in response to growing road networks

JOURNAL OF APPLIED ECOLOGY, Issue 5 2008
Jacqueline L. Frair
Summary 1The ecological footprint of a road may extend for several kilometres with overlapping effects from neighbouring roads causing a nonlinear accumulation of road effects in the landscape. Availability of preferred habitat, spatial dependencies between roads and habitat types, and fidelity to traditionally used areas further confound our ability to predict population-level responses of animals to growing road networks. 2To isolate these effects, we developed an individually based movement model using elk Cervus elaphus L. as a model system. Empirically derived movement rules redistributed elk under different amounts of preferred habitat (clearcuts), road densities, and road development schemes. We tracked potential mortality risk (given time spent near roads) and emigration rates (given declining accessibility of foraging habitat). 3Design of the road network accounted for up to 30,55% difference in mortality risk and emigration rates, with the largest differences occurring at intermediate road densities (1,1·5 km km,2) when road effects began to saturate the landscape. Maintaining roads in association with clearcuts caused a decline in habitat accessibility equivalent to replacing 50,75% of these foraging patches with conifer forest. A nine-fold difference in potential emigration was observed after varying elk tolerance for declining habitat accessibility despite holding local movement biases constant. 4Elk responses to growing road networks were non-linear, exposing thresholds for road density that were reflected in the home range occupancy patterns of a large sample of elk in the region. 5Synthesis and applications. Our approach provides a means of scaling-up complex movement decisions to population-level redistribution, separating the confounding effects of landscape context from road effects, and exposing thresholds in connectivity and mortality risks for wildlife caused by infrastructure growth. Our model indicated that road densities , 0·5 km km,2 yielded the highest probability of elk occurrence where elk were hunted (and sensitive to roads), but disassociating roads from foraging habitats or managing human access to roads may maintain effective elk habitat at substantially higher road densities. [source]

The first named Ediacaran body fossil, Aspidella Terranovica

PALAEONTOLOGY, Issue 3 2000
James G. Gehling
Aspidella terranovica Billings, 1872 was first described from the late Neoproterozoic Fermeuse Formation (St. John's Group) on the Avalon Peninsula of eastern Newfoundland, approximately 1km stratigraphically above the famous Ediacaran biota at Mistaken Point, and several kilometres below the base of the Cambrian. Aspidella has been reinterpreted perhaps more than any other Precambrian taxon, and has variously been regarded as a fossil mollusc or ,medusoid', a gas escape structure, a concretion, or a mechanical suction mark. Our studies indicate that Aspidella includes a wide variety of preservational morphs varying from negative hyporeliefs with a raised rim and ridges radiating from a slit (Aspidella -type preservation), to flat discs with a central boss and sharp outer ring (Spriggia preservation), to positive hyporeliefs with concentric ornamentation (Ediacaria preservation). Specimens occur in a continuum of sizes, with preservational styles dependent on the size of the specimen and the grain size of the host lithology; the elongation of specimens is tectonic. Aspidella is confirmed as a body fossil from observations of complex radial and concentric ornamentation, mutually deformed borders in clusters of specimens, and occurrence on the same bedding planes as certain distinctive Ediacaran taxa. Aspidella is indistinguishable from, and has priority over, several of the most common genera of late Neoproterozoic discoidal body fossils worldwide. Similar fossils from Australia are interpreted as holdfasts of frond-like organisms. The density of specimens in the Aspidella beds suggests levels of benthic biomass in the Neoproterozoic that could rival those of modern marine communities. The serial growth forms, PalaeopascichnusIntrites, Neonereites renariusYelovichnus, associated with Aspidella, are interpreted as body fossils of unknown affinities rather than trace fossils. A new, trilobed, Ediacaran body fossil, Triforillonia costellae gen. et sp. nov., is described from the Aspidella beds of the Fermeuse Formation. [source]

A study of thermals in cumulus clouds

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 607 2005
Alan M. Blyth
Abstract Air motions in the thermals contained within shallow Florida cumulus clouds were observed to be similar to the circulation observed in laboratory thermals. There was outward flow in the updraughts of individual thermals at most levels and there were usually downdraughts observed at the edges of the updraught or of the cloud. Widespread inward flow towards the centre of the cloud and a narrow, but strong, updraught was occasionally observed, reminiscent of the tail found at the rear of the laboratory thermals. A region of reduced liquid water content was frequently observed in the centre of several thermals where the updraught and horizontal 1D divergence were strongest, and complete holes were observed on two occasions. Although horizontal wind shear was generally weak, it was significant in a few cases, causing the flow pattern in the cloud to be asymmetric. Ascending regions of cloud with high values of liquid water content (cloud cores) were commonly observed at all altitudes, but generally the percentage of clouds measured with high liquid water content decreased with altitude. The observations of airflow and liquid water content structure in warm cumulus clouds described in this paper are consistent with the schematic model of a thermal where a core of high liquid water content survives for several kilometres above cloud base, but erodes as it ascends. Copyright © 2005 Royal Meteorological Society [source]